industrial chemistry 2

HSC Chemistry Option Module: Industrial ChemistrySummary

Page | 1Robert Lee Chin

Industrial Chemistry: 1. Replacements for natural products Identify data, gather and process information to identify and discuss the issues

associated with the increased need for a named natural resource that is not a fossilfuel and evaluate the progress currently being made to solve the problemsidentified.

Discuss the issues associated with shrinking world resources with regard to oneidentified natural product that is not a fossil fuel, identifying the replacementmaterials used and/or current research in place to find a replacement for the namedmaterial.

Natural product: RubberNatural rubber is an elastomer (elastic hydrocarbon polymers) originally derived from latex,the milky colloid found in some plants. The commercial source of rubber is the Para rubbertree- rubber therefore a renewable resource.

The uses of rubber are widespread, from household items to many uses in medicine andindustry: tires (the majority is used for this), hoses, belts, matting, flooring, gloves, toyballoons, rubber bands, pencil erasers, textiles, even spacecrafts.

In addition, the rubber wood can be used as timber for quality furniture and construction oncethe tree becomes unviable for rubber production. It is strong, flexible, resistant to microbesand easy to work with.

Flow Chart for conventional rubber production:Rubber tree cultivation: tropical countries i.e. South-East Asia, Africa, South America

provide optimum growing conditions, with up to 25 year productive phase

Tapping: Outer layer of bark is cut off and latex is collected in containers supported bywires attached to the trunk of the tree

Collection: Latex is transferred to air-tight containers for ammoniation (ammonia preventslatex from coagulating)

Processing: processed into latex concentrate for dipped products, or coagulated under cleanconditions using formic acid

Grading: Rubber is process into various grades (higher grades have size reduction andcleaning process to remove contaminants)



Final processing and packaging: Rubber is dried, then baled, pelletized and packagedready for shipping

Problems with natural rubberThe production of rubber trees has environmental and political issues relating to thesmallholders who grow the crop.

Over 90% of natural rubber production occurs in developing nations with tropical climatesincluding Thailand, Malaysia, Indonesia, South America and most recently, Africa. A“slash-and-burn” approach is used, leading to land degradation, air pollution anddeforestation. End of season burn-offs are used to increase plantation area which has seen theemergence of new diseases previously isolated within the forest.

Rubber growers have little economic incentive to improve the quality of their product as theyhave little bargaining power compared to the intermediate traders. As a result, they oftenleave contaminants in unrefined rubber in an attempt to be paid more for the weight of therubber. Scarcity of land for rubber plantations has led to escalating land prices, leavingownership of viable land to a few elite farmers. There are food shortages as the result of landbeing used for Rubber plantations rather than crop staples.

Reasons for solutions:*Some people are severely allergic to proteins in latex products, which can causeoccupational problems esp. in the healthcare industry.*Rubber plantations in Asia are affected by a fungal disease that could potentially decimatecurrent production. *There are also predicted shortages of supply due to economic developments in China andIndia*Today, 75% of rubber production is a synthetic product derived from petroleum. Althoughthis is a cheap way to produce rubber, petroleum is a non-renewable resource which is rapidlydepleting. Therefore, there is great need for an alternative source of rubber.* Synthetic rubber is poorer quality and cannot be used for high impact purposes such asaeroplane tyres and tyres carrying heavy loads.

Solutions to resource shortageSeveral substitute plants are being trialled to enhance global production of rubber, the mostpromising is a Mexican shrub called guayule. Guayule has the benefits of:

-the potential to reduce environmental effects as it can tolerate more arid conditions-less likely to cause allergic reactions than latex from rubber trees

2. Equilibrium processes in industrial processes

Identify data, plan and perform a first-hand investigation to model an equilibriumreaction



Choose equipment and perform a first-hand investigation to gather informationand qualitatively analyse an equilibrium reaction

First-hand Investigation: Systems at equilibrium

Aim: To examine the effects of changing reaction conditions on a system at equilibrium

Materials:Dilute solutions (0.1 M) of:

- Iron (III) chloride-potassium thiocynate (KSCN)-potassium chloride (KCl)-Iron (III) nitrate (Fe[NO3]2)-sodium hydroxide (NaOH)

Method:1. Place equal volumes of iron(III) chloride and potassium thiocyanate into a test tube

and allow equilibrium to be established; a blood-red solution will form.2. Dilute solutions with distilled water until colour lightens3. Place equal volumes of the diluted solution into five separate test tubes4. Add a small volume of KCl to the first test tube5. Repeat step 4 with Iron(III) nitrate for the second test tube6. Repeat with KSCN for the third test tube7. Repeat with NaOH for the forth test tube.

Results:

The reaction between Iron(III) chloride and Potassium thiocyanate

(KSCN):

Chemicaladded to

FeCl3 andKSCN

Chemicaldisturbing

equilibrium

Observationregarding colour

Shift in equilibrium andexplanation

KCl KCl Lighter red Increasing the concentration ofone of the products shiftsequilibrium to the right

Fe[NO3]2 Fe[NO3]2 darker red Adding Fe3+ ions increases theconcentration of reactants; shift

to rightKSCN KSCN Darker red Increasing the concentration of

one of the reactants shiftsequilibrium to the right

NaOH NaOH Orange (precipitate) Fe3+ ions react with OH- ions toform a yellow orange ioncomplex; shifts left???



Conclusion: Changing the concentrations of reactants and products in an equilibrium, oradding a substance that will react with either products or reactants, will have an effect on theequilibrium position. Increasing the concentration of a reactant or a substance that reacts witha product will shift the equilibrium to favour the products. Conversely, Increasing theconcentration of a product or a substance that reacts with a reactant will shift the equilibriumto favour the reactants.

Explain the effect of changing the following factors:-Concentration-Pressure-Volume-temperature

Le Chatelier’s PrincipleWhen a system that is at equilibrium is changed by altering temperature, concentration ofproducts and/or reactants or the volume/pressure of gas; the equilibrium shifts to counteractthe effect and return the system to equilibrium

ConcentrationAn increase in temperature will cause:-An exothermic reaction to reverse. Products will decompose into reactants i.e. concentrationof products will decrease while concentration of reactants will increase. The reverse occurs ifthe temperature of the system is lowered.-An endothermic reaction to proceed as written. The reverse occurs if the temperature of thesystem is increased.

Pressure and volumeAn increase in pressure and volume will cause-changes to occur in gases only-same effect as decreasing volume of the reaction vessel, as the particles are forced to occupyless space-equilibrium favours the side with least number of moles of gas

ConcentrationAn increase in concentration will cause:-equilibrium to shift to maintain the molarities of products and reactants i.e. if more reactantsare added, it will shift to produce more product and vice versa.

Process and present information from secondary sources to calculate K fromequilibrium conditions



The extent to which an equilibrium reaction can be quantitatively defined using theequilibrium constant, K. When the value of K is large, the equilibrium is towards the productside. When K is small, it is towards the reactant side.

If we define the general homogenous (same chemical state i.e. solid, liquid or gas)equilibrium reaction as: , then K is defined as:

, where [ ] denotes concentration in molL-1

Examples:

1) Consider the equilibrium:

At a certain temperature 3.0 moles of F2 and 2.0 moles of I2 are introduced into a10.0 L container. At equilibrium, the [I4F2] is 0.02 M. Calculate the K for thereaction.

Reactants ProductsConcentrations

(molL-1)I2 F2 IF5 I4F2

Initialconcentration

0.2 0.3 0 0

Δ concentration -3(0.02) = -0.06 -6(0.02) = -0.12 +2(0.02) = 0.04 +0.02Equilibrium

concentration0.14 0.18 0.04 0.02

Interpret the equilibrium constant expression (no units required) from the chemicalequation of equilibrium reaction

If K is large, the equilibrium lies to the right, so the concentration of products is high and thereaction almost goes to completion. If K is small, the equilibrium lies to the left, so there isvery little reaction. The size of the K value is an indication of the relative strength of acidsand bases, or the solubility of a substance.

Points to remember:

System at equilibrium



*When calculating K, disregard any reactants or products in solid or liquid (solvents) state*the concentrations used refer to the concentrations of reactants and products at equilibrium

Identify that temperature is the only factor that changes the value of the equilibriumconstant (K) for a given equation

The value of K for a given equilibrium is unaffected by changes in concentration or theaddition of a catalyst, which simply increases the rate of both forward and reverse reactions.

For exothermic reactions, K decreases with increasing temperatures as the equilibriumfavours the reactants. Conversely, K increases with decreasing temperatures, as it favours theproducts

For endothermic reactions, K increases with increasing temperatures because the equilibriumfavours the products. Conversely, K decreases with decreasing temperatures, as it favours thereactants

For example, in the oxidation of sulfur dioxide is an exothermic equilibrium:

,

Heating the reaction vessel will shift the equilibrium to the left. This will increase the valuesof [O2] and [SO2] and decrease [SO3], therefore K will be smaller. However, if the vessel iscooled, equilibrium will shift to the right i.e. [SO3] will increase while [O2] and [SO2] willdecrease, so K will be larger.

3. Sulfuric Acid

Outline three uses of sulfuric acid in industry

Sulfuric acid is one of the most important industrial chemicals, with many applications:

*Used by fertiliser industry (~70% total production) to make ammonium sulfate andsuperphosphate*Removes oxides and grease from steel and iron before galvanising or electroplating*Dehydration agent i.e. removes water liberated during manufacture of explosives, dyes,detergents, polymers, esters, electrolysis of sodium chloride solution*Electrolyte in vehicle batteries*Used in the production of nitroglycerine for explosives and as a vasodilator (treatment ofheart conditions)



Describe the processes used to extract sulfur from mineral deposits, identifying theproperties of sulfur which allow its extraction and analysing potentialenvironmental issues associated with its use

Elemental sulfur occurs in deposits near volcanoes, hot springs and underground. It is alsofound in ores e.g. PbS, hydrogen sulfide in fossil fuel sources and sulfates in the ocean

Extraction of Sulfur

Frasch Process:Sulfur is extracted from underground sources by the Frasch process. This process relies on thefollowing properties of sulfur:

-relatively low melting point (113°C) and boiling point (445°C)-low density-insolubility in water

There are 4 main steps:

1. 3 concentric pipes are drilled to the deposit2. Superheated steam (160°C) under is pumped through the outer pipe, melting thesulfur3. Air under high-pressures is pumped through the inner pipe, pushing the low-densityliquid sulfur foam around the middle pipe to the surface4. The insoluble sulfur is easily separated without the need to evaporate the water.Slight cooling causes the sulfur to solidify and settle out.

Natural gas andpetroleum:Extracted fromhydrogen sulfide

(H2S) in natural gas andpetroleumdeposits. The

sulfur is produced inincomplete combustion of H2S:

1. The mixture is cooled to condense the sulfur and passed over a heated catalyst:

Moltensulfur

Superheated water

Hot, compressed air

Sulfur



2. The mixture is cooled again to condense the remaining sulfur.

Smelting or metal oresSulfur may also be released as sulfur dioxide when metal oxide ores are smelted. The generalequation, using M to represent the metal is:

Environmental IssuesSulfur dioxide readily dissociates with water to form sulphurous and sulfuric acid, thusproducing acid rain. Acid rain lowers the pH of soil and water sources, potentially damagingthe environment and also contributes to chemical weathering of statues and metal. Most ofthe sulfur dioxide produced by metal smelting is used to make sulfuric acid and sulfur dioxideemissions into the atmosphere are strictly controlled by government regulations.

Also produced during mining and smelting is hydrogen sulfide (H2S), a gas more toxic thancyanide. Soluble substances such as arsenic may be brought to the surface

Outline the steps and conditions necessary for the industrial production of H2SO4from its raw materials

Describe the reaction conditions for the production of SO2 and SO3 Gather, process and present information from secondary sources to describe the

steps and chemistry involved in the industrial production of H2SO4 and useavailable evidence to analyse the process to predict ways in which the output ofsulfuric acid can be maximised

Production of SO2 and SO3Combustion of sulfur or metal sulfides occurs in a combustion furnace as an exothermicreaction. Conditions that favour high rate of reaction and yield are high temperature andsurface area (by crushing rock).

Molten sulfur from the Frasch process is filtered to remove impurities and lime (calciumhydroxide) is added to reduce the acidity, thus preventing corrosion. In the combustionchamber excess dry oxygen is used to maximise the yield of SO2.



SO2 derived from smelting of metal ores mustbe purified and dried before going to theconverter:

The production of SO3 from SO2 and O2 is an equilibrium reaction involving a compromisebetween reaction rate, product yield and economic factors. The following conditions producea yield of over 98%:

*High temperatures increase rate of reaction, but the equilibrium is exothermic and hightemperatures may damage the catalyst. 450 - 600°C provides a compromise. *The vanadium pentoxide or platinum catalyst increases the rate of reaction by lowering theactivation energy for the reaction.*A multi-stage process is used to convert the SO2 into SO3. With each new stage the

temperature is reduced, thus shifting the equilibrium to the right. This produces a yield ofover 98%.*Increased pressure shifts the equilibrium to the right, but this is expensive, so pressures of1-2 atmospheres are used*Increasing the concentration of the reactants pushes the reaction to the right. From thereaction, the stoichiometic ratio of O2:SO2 is 1:2. Industrially, twice as much O2 is used i.e.

1:1 ratio.

Production of H2SO4Sulfuric acid is manufactured using the contact process. There are 4 main steps involved:

1. Combustion ChamberPure sulfur or sulfide ore is combusted in air at 1000°C to produce sulfur dioxide:

2. ConverterSulfur dioxide is passed into a tower is passed into a tower made of stacked vertical beds ofvanadium pentoxide (V2O5) or platinum catalyst. It is oxidised to sulfur trioxide in anexothermic equilibrium reaction, with temperatures of 450 - 600°C used as a compromise.High pressures also shift the reaction to the right.

CombustionfurnaceMolten sulfur SO

Dry air underpressure

SO2

Metal

SO2

Steam

SO2smelter Waterscrubber

Electrostaticprecipitator

Dryingtower

O2 DrySO



3. Absorption TowerSulfur trioxide cannot immediately be mixed with water, as it forms a fine mist which isdifficult to collect. Instead the gas is bubbled through very concentrated sulfuric acid inabsorption towers to form Oleum (disulfuric acid), H2S2O7.

The sulfuric acid used to dissolve the SO2 must be maintained at 70°C and 98%

concentration to ensure maximum absorption. The concentration is important because at 98%concentration, the vapour pressure of SO3 above H2SO4 is a minimum. Concentrationsgreater than 98% and the water vapour pressure (high vapour pressure at normal temperatures= volatile) increases sharply, causing the resulting acid mist to evaporate. The acid is alsoconcentrated at a rate to minimise an increase in concentration

4. Hydration of Oleum:Oleum is converted into concentrated sulfuric acid by the addition of dilute sulfuric acid andwater. The reaction is highly exothermic, so the acid needs to be cooled before storage.

Traditionally, mild steel was used for the manufacturing equipment. The trend is now to useTeflon coated piping to reduce contamination of the acid due to iron corrosion.

Apply the relationship between rates of reaction and equilibrium conditions to theproduction of SO2 and SO3

Condition Increasereaction rate

IncreaseEquilibriumyield

Economicfactors

Conditions used

Temperature Hightemperatures

Lowtemperatures

High temp.Expensive and

damagescatalyst

450-600°C

Pressure n/A High pressures High pressuresare expensive

1-2 atm.

Concentrationof reactants

n/A Increasingreactant

concentration

Increasing SO2is more

expensive thanincreasing O2

Excess O2O2:SO2 is 1:1

Concentrationof products

n/A Removal ofproducts

n/A Removing SO3 asit is produced



Other Catalyst n/A Reducesactivationenergy andtherefore,reaction

temperature

Vanadiumpentoxide/platinu

m

Unreacted gases Recycling backin reaction

vessel

Efficient;maximises

yield

Recycling ofUnreacted O2 and

SO2

Perform a first-hand investigation to observe the reactions of sulfuric acid acting as:-an oxidising agent

-a dehydrating agent

Sulfuric acid as an oxidising agentThe addition of sulfuric acid to zinc metal liberates hydrogen gas.

Sulfuric acid as a dehydrating agentAddition of sulfuric acid to sugar (sucrose, C12H22O11)

Aim: To observe the reactions of sulfuric acid acting as an oxidising agent and as adehydrating agent

Equipment:-Concentrated sulfuric acid-Granulated Zinc metal-matches-Table sugar (sucrose)-Glass beaker-Glass stirring rod

Safety: concentrated sulfuric acid is highly corrosive and toxic and may cause severe burnsto the body. ALWAYS add acid to water, stirring constantly. Use sodium bicarbonate toneutralise any spills. Wear acid-resistant safety glasses, gloves and aprons at all times. Avoidinhaling fumes, and use a well-ventilated area, or if possible, a fume cupboard. If contactwith acid occurs, run under cold tap water for at least 15 minutes

Method:As an oxidising agent:

1) Place a small amount of granulated zinc metal into a glass beaker2) Slowly add a small volume of concentrated sulfuric acid and place a lid over the

beaker. Zinc bubbles should begin forming on the zinc surface.3) After several minutes, place a lit match into the beaker. You should hear a loud ‘pop’,

indicating the presence of hydrogen gas

As a dehydrating agent:1) In a fume cupboard, add a small amount (50 g) of sucrose to a 250mL beaker



2) Slowly pour in concentrated sulfuric acid to just cover the sucrose. After a fewminutes you should observe the beaker becoming hotter,the cusorse reacting to form atower of black carbon and sulfur oxide fumes emerging from it.

Results:As an oxidising agent:The addition of hot concentrated sulfuric acid to zinc metal liberates sulfur dioxide gas andwater as shown: In the process zinc becomes

zinc sulfate i.e. zinc is oxidised (oxidation state changes from 0 to +2).

As a dehydrating agent:The addition of concentrated sulfuric acid to sucrose forms carbon, water and sulfuric acid ina highly exothermic reaction which causes most of the water to form steam:

Describe and explain the exothermic nature of sulfuric acid ionisation

The ionisation of sulfuric acid is a rapid, highly exothermic reaction. It occurs in two steps:

In the first dissociation, H2SO4 acts as a strong acid as Kc approaches infinity. In the second

dissociation, HSO4- is a weak acid, so Kc is small.

Identify and describe safety precautions that must be taken when using and dilutingconcentrated sulfuric acid

Diluting sulfuric acid is potentially hazardous due to the vigorous exothermic nature duringionisation.

Safety PrecautionsWear protective equipment and clothing, especially safety glasses.

ALWAYS ADD ACID TO WATER. Add a small amount at a time, stirring constantly(sulfuric acid is much denser than water and this may cause a layer of concentrated acid toform at the bottom, forming a steep temperature gradient). This produces a dilute solution,releasing only a small amount of heat which can be absorbed by the water. Any splatters thatdo occur are more likely to be dilute than concentrated. If spills do occur, clean up with largeamounts of water and sodium hydrogen carbonate (bicarbonate soda).

If water is added to concentrated acid, the heat released will make the water boil violently,splattering droplets of concentrated acid out of the container. The heat generated may beenough to crack the container.



Use available evidence to relate the properties of sulfuric acid to safety precautionsnecessary for its transport and storage

Due to its corrosive nature (low pH), it must not be transported with foodstuffs,dangerous-when-wet substances, oxidising agents, organic peroxides, toxic substances andradioactive substances.

In high school science labs, dilute sulfuric acid is stored in glass/plastic containers with atightly-fitting lid, so that it does not react with moisture in the air. Commercially, it istransported in its pure molecular form in steel containers as there is no water for it to ioniseand react with the metal. It MUST NOT be stored with foodstuffs, oxidising agents andorganic or combustible materials (it oxidises carbohydrates, causing them to char), or metals(liberates explosive hydrogen gas). Its high vapour pressure means it is volatile, so it must bestored in well-ventilated areas.

4. Sodium Hydroxide

Explain the difference between galvanic cells and electrolytic cells in terms ofenergy requirements

There are two types of electrochemical cells: galvanic cells and electrolytic cells.

In galvanic cells a redox reaction takes place spontaneously to produce electricity. It consistsof two half cells with separate electrolytes and a salt bridge to complete thecircuit.

In galvanic cells, the anode is negative and the cathode positive

In electrolytic cell a compound is decomposed by passing electricity. It is not spontaneous; itis forced by applying a voltage;

In electrolytic cells, the anode is positive potential and the cathode has the negative potential

Identify, plan and perform a first-hand investigation to identify the products ofthe electrolysis of an aqueous solution of sodium chloride

Investigation: Electrolysis of Aqueous Sodium Chloride

Aim: To determine the products of the electrolysis of aqueous sodium chloride or brine



Background: Electrolysis is a process that uses electricity to decompose ionic compounds.The ion are caused to migrate to the charged electrodes and pure elements will form.Electrolysis is also used in industry in the purification of active metals such as aluminium andsodium.

Materials:-carbon electrodes-transformer-brine or salt solution-phenolphthalein in dropper bottle-voltameter

Carbon Electrode Method:1/ Place brine solution into a beaker2/ Place two carbon electrodes into the

beaker and connect to the transformer.3/ Set to DC 8V and allow the current to

run for a few minutes.4/ Add drops at the cathode of the circuit,

observe.5/ Add a few drops at the cathode,observe.



Voltameter Method:1/ Place a few drops of phenolphthalein

indicator into a beaker containingbrine solution.

2/ Fill the voltameter with the brinesolution.

3/ Connect to the DC terminal of atransformer and allow 8V to flowthrough the voltameter.

4/ Observe the voltameter and test thegases collected above both the cathodeand the anode.

Results:

Equations:Anode (positive electrode) reaction:

Cathode (negative electrode):

Net ionic reaction:

Minimum voltage requirement:

Analyse information from secondary sources to predict and explain thedifferent products of the electrolysis of aqueous and molten sodium chloride

Electrolysis of pure, molten sodium chlorideIf pure, molten NaCl undergoes electrolysis, the result is the decomposition of the compoundinto its element. Chloride ions are oxidised to form chlorine gas at the anode:

cathodeanode



At the cathode, sodium ions are reduced to form pure sodium metal:

As there are only 2 species involved, the only products that will form are chlorine gas andsodium metal.

Electrolysis of aqueous sodium chlorideIn an aqueous sodium chloride solution, electrolysis may produce different products becausewater can also participate in reactions. There are 2 possible reduction reactions at the cathode:

The water reduction has a significantly lower voltage requirement, so it will proceed. If anysodium metal did form, it would instantly react with the water anyway.

There are also 2 possible reactions at the anode:

Because the voltage requirements are very similar, the reaction that occurs will depend on theconcentration of the reactants. In a dilute solution, oxygen gas would be produced as therewould be mostly water molecules. In a concentrated solution, however, a mixture of the twowould be produced. In the industrial process to manufacture NaOH, the salt solution used isso saturated, that pure chlorine gas is produced.

Outline the steps in industrial production of sodium hydroxide from sodiumchloride solution and describe the reaction in terms of net ionic and full formulaequations

Distinguish between the three electrolysis methods used to extract sodiumhydroxide:

-mercury process-diaphragm process-membrane process

by describing each process and analysing the technical and environmentaldifficulties involved in each process

The electrolysis of sodium chloride to produce sodium hydroxide and chlorine is known as achloralkali process.



Electrolysis of sodium chloride to produce sodium hydroxide and chlorine is performed using3 types of electrolytic cells: mercury, diaphragm and membrane cells. The main technicaldifficulty in all methods is preventing the chlorine produced contacting (and therefore,reacting) with the sodium hydroxide or hydrogen.

A saturated brine (NaCl) solution is used in all 3 cells. Impurities are first removed as asludge by precipitation reactions:

-Calcium:

-Magnesium:

-Iron

-sulfate:

Despite using different methods, all 3 cells achieve the same overall reaction:

The Mercury ProcessIn the mercury cell, titanium coated with a rare earth metal is the anode. A saturated brine(NaCl) solution floats above cathode, which is a thin layer of mercury at the bottom. Chlorinegas is oxidised at the anode and pumped away:

Sodium is reduced at the cathode: , where is forms an amalgam (Na/Hg)

with the mercury and is constantly removed.

Electrolysis prevents the amalgam reacting with the brine. The amalgam pumped to adecomposing vessel where it is reacted with water to form sodium hydroxide and water:

Although the mercury is recycled, the mercury cell is being phased out due to concerns ofmercury pollution, particularly of aquatic environments. The NaOH produced is 50% (0.5 M)concentrated- suitable for commercial purposes.



TheDiaphragm ProcessIn the diaphragm Cell theproducts of electrolysisare kept apart using apermeable asbestosdiaphragm. This providesa lining for thesteel-mesh cathode. Theanode is a rod of solidgraphite. Electrolysisoccurs when the brinesoaks through theasbestos to the cathode.Hydrogen gas isdischarged at the cathode:

In an aqueous environment the reduction of sodium does not occur. Chlorine gas isdischarged at the anode:

Sodium ions (spectator ions) from the brine are attracted to the cathode and with thehydroxide ions produced at the cathode, are washed to the bottom where a caustic brine(NaOH/NaCl) leaves the cell. The NaOH must be concentrated to 50% and the salt removedvia evaporation. The salt may then be reused to form brine.

The overall cell reaction:

This cell is slowly being phased outdue to the asbestos used, which poses aserios health hazard as it iscarcinogenic and may causelife-threatening respiratory diseasessuch as asbestosis and mesothelioma.Another disadvantage is that isproduces low purity NaOH- only

about 12% pure. This is because some of the chloride ions can seep through, thuscontaminating the NaOH.

To Ti anode

Brine

H2(g)Na/Hg

H2O(l)

Cl2(g)

Decomposer

Cl2(g)

NaOH(a

Cold water

Hot water

Mercury coolerand pump

+

To Hg cathode _

Membrane cell

Asbestosdiaphragm

Graphiteanode

NaOH solution

Steam

Steel-mesh

Cl2(gH2(g)Brine

Spend solution



Membrane CellThe membrane cell is the most recent cell due to the recent development of high-tech Teflonmembrane. It has a titanium anode (will not react with chlorine gas) and a nickel cathode.Anode and cathode compartments are separated by an ion exchange that allows water andpositive ions i.e. Na+ to diffuse through, but not negative ions. Brine is pumped into theanode compartment where chlorine ions are oxidised to form chlorine gas, which is pumpedaway:

At the cathode, water is reduced to hydrogen gas and hydroxide ions:

Sodium ions migrate to the cathode compartment where they combine with the hydroxideions to form NaOH. Unfortunately, the brine is able to migrate to the cathode compartment,thus reducing the purity of the NaOH obtained, so further purification is needed. Overall cellreaction is the same as for the diaphragm cell.

The membrane cell is likely to replace the other two, as it has the least environmental impactand is very energy efficient as the electrodes can be placed very close to each other. Itproduces NaOH of about 30-40% purity (mixture contains NaCl from brine), so furtherpurification is needed to increase purity to 50%.

Property Mercury Cell Diaphragm Cell

Membrane cell

Cathode Hg Steel-mesh NickelCathode product Na/Hg amalgam NaOH(aq)

NaCl(aq)H2(g)

NaOHH2(g)

decomposer NaOH n/A

Ni cathodeTi anode

H2O(l)

NaOH(aq)Brine out

Brine in

Cl2(g H2(g

Na+(a



H2(g)Anode Titanium coated with

rare-earth metalTitanium/titanium steel-alloy/graphite

Anode product Cl2(g)NaOH purity 50% 12 – 15% ~40%Operating voltage 4.0 – 4.5 4.0 – 5.0 3.0 – 4.0 Cell temperature(°C)

90 – 95 75 – 85 88 – 90

Mercury Cell Diaphragm Cell Membrane CellEnvironmentalIssues

Use of mercury and itsdisposal:

-poses hazard to aquaticenvironments

Use of asbestos andits disposal:

-expensive to remove-not readilydecomposed

-small fibres remainsuspended in air for

long periods

n/A

Technical Issues Chlorine gas is toxic:-must wear protective breathing apparatus-check for leaksChemicals used are corrosive to metal surfaces and bricks:-maintenance is expensiveHydrogen is highly reactive with chlorine and oxygen:- check for leaks esp. diaphragm and membrane cellsMercury is toxic:-check for leaks-safe disposal

n/A

Use of electricity creates heat:-size of gap between electrodes must be controlled by computer.-size of gap determines operating voltage and therefore, productioncostsQuality control:-NaOH concentration (titration)-impurity metal ions in brine (AAS)-impurities in Cl2, H2, O2 (gas chromatography)

1. Saponification

BackgroundTriglycerides



A triglyceride is the general name for a compound containing 3 “fatty acid” molecules joinedto one “glycerol” molecule. Triglycerides are esters.

Fatty acids are long-chain hydrocarbons with a carboxylic (-COOH) group at one end, whichis either saturated or unsaturated.

Schematically, fatty acids can be represented by:

Glycerol is a ‘triple alcohol’ i.e. it contains 3 OH- functional groups. Systemically, it isnamed ‘propantriol’

Fats and oils are both types of triglycerides. The difference is that fats are solid at roomtemperature due to all single C–C bonds, therefore they are said to be saturated. Oils areliquid at room temperature due to the presence of many double C=C bonds i.e. it is‘unsaturated’.

Polar andhydrophilic/lipophobic

–COOH groupNon-polar and hydrophobic/lipophilic

hydrocarbon chain

polar –OHfunctional

groups

Non-polarHydrocarbon chain



Describe saponification as the conversion in basic solution of fats and oils toglycerol and salts of fatty acids

Saponification is the reaction in which an ester is ‘hydrolysed’ with a strong base (e.g. NaOH,KOH) to produce glycerol (alcohol) and salts of fatty acids (carboxylic acid). If the fatty acidwas oleic acid and the base KOH, then the soap

molecule produced would be potassium oleate,C18H33KO2

describe the conditions under which saponification can be performed in theschool laboratory and compare these with industrial preparation of soap

The saponification (SAP) value is a measure of the amount of base required to saponify 1gram of an ester. This value is a measure of the average molecular weight of the all the fattyacids.

Long-chain fatty acids, found in fats, have low SAP values due to fewer –COOH groupscompared to short-chain fatty acids.

Laboratory SaponificationIn the lab, soap can be made by heating a mixture of soap or oil with NaOH or KOH. Thesoap produced can be precipitated by using a saturated sodium chloride solution and washedto remove excess glycerol and base. Dilute acid can be used to neutralise and excess base.

Industrial SaponificationIndustrially, soap can be prepared in one stage (Kettle Boiled Batch process) or two stages(fatty acid neutralisation process). Obvious differences in both of these processes ascompared to laboratory scale are:

-a mixture of fats and oils are used e.g. palm, olive and coconut -huge reaction vessels are used, up to 120 tonnes -elevated temperatures and pressures (makes water more soluble in fats) -metal-based catalyst

-the shape size and internal roughness of the reaction Bessel must be considered-glycerol is removed and used for other purposes

Fatty-acid neutralisation processThis process uses two steps:

The first step hydrolyses the triglycerides to form fatty acids and glycerol, the reverse ofesterification. A zinc-oxide catalyst improves the reaction rate. The fatty acids flow upwardsto a vacuum dryer, while the glycerol/water mixture is pumped away and separated viadistillation.



The second step neutralises the fatty acids with precise amounts of a strong base (determinedfrom SAP value) to form the sodium/potassium fatty-acid salt (soap).

Kettle Boiled Batch ProcessAs the name suggests, this process takes place in large, open steel tanks called ‘kettles’. Thereaction mixture is kept constantly boiling via injection of high pressures, which also helpskeep the reaction mixing. Soap from previous reactions is kept to help the water and oilemulsify. Batch process refers to a reaction where all the reactants (oil, base, salt, catalyst,water) are added at the beginning and the products removed at the end.

At the end of this process, extra salt is added to help solidify the soap. Extra steam is addedand the mixture settled to remove the glycerol.

The main difference compared to the lab process is the use of high pressure steam tohydrolyse the fats/oils.

account for the cleaning action of soap by describing its structure explain that soap, water and oil together form an emulsion with the soap acting

as an emulsifier

What is an emulsion?An emulsion is a mixture formed when two or more normally immiscible substances form astable mixture which does not separate. It is not to be confused with a solution, as non of themolecules are associated with each other. Instead, one of the liquids is evenly dispersedthroughout the other, through the action of another chemical called an emulsifier.

Each emulsion has two different types. For example, if the two liquids were oil and water, thetwo emulsions would be:

-oil suspended in water e.g. sorbolene cream -water suspended in oil e.g. mayonnaise

What are surfactants?Surfactants are chemicals which reduce the surface tension of liquids by adsorbing at theinterface of two different liquids. Surfactants may act as: detergents, wetting agents,emulsifiers, foaming agents and dispersants. In soaps and detergents, surfactants make iteasier for water to emulsify with oil/ grease.

Soap as an emulsifierThe use of soap as a cleaning agent is dependent on its ability to emulsify dirt/grease in water.Most dirt is non-polar and oils/grease is non-polar long-chain hydrocarbons. Water is polar,thus it is immiscible with dirt and grease.



When soap is placed in water and agitated, its ions dissociate (the positive ion takes no part inthe cleaning action). The negative fatty acid ions, called the surfactant (surface acting agent)do not disperse evenly. Instead, they form clumps with the polar –COOH heads stickingoutwards. The –COOH groups form hydrogen bonds with water. This spherical structure iscalled a micelle.

Non-polar grease/dirtmolecules areencapsulated anddissolved by the non-polarlipophilic core of themicelle, thus forming anemulsion between water

and oil. This emulsion keeps the grease molecules suspended, which can be carried away bywater.

Distinguish between soaps andsynthetic detergents in terms of:-the structure of the molecule-chemical composition-effect in hard water

Detergents are artificial soaps, invented during the 1940’s and have largely replaced soap incleaning because they are more powerful emulsifiers and because they can be modified tospecialised applications.

While soaps are made from animal and vegetable oils and manufactured via saponification(heating triglycerides with a strong base), detergents are derived from petroleum. An alkanolfrom petroleum is reacted with Sulfuric acid to a sulfur-containing acid, which is then reactedwith a strong base.

Composition and structure of detergentsThe composition of detergents is similar to soaps in that both contain long hydrocarbonchains. The difference lies in that while soaps are sodium/potassium salts, detergents arehydrocarbons with a sulfate or sulfonate functional end group.

Structurally, they both contain an ionic or polar head and a non-polar hydrocarbon tail.However while soaps act only as anionic surfactants, detergents can act as anionic, cationic ornon-ionic surfactants.

Non-polar lipophilichydrocarbon chainsdissolve triglycerides

Hydrophilic -COOH groupforms hydrogen bonds

with water

Suspended grease



Effect in hard waterHard water contains significant concentrations of magnesium and calcium ions. Soap will not‘lather’ in hard water as it forms a precipitate ‘scum’ which accumulates on surfaces.Detergents will lather in hard water and they do not form precipitates.

distinguish between anionic, cationic and non-ionic synthetic detergents in terms of:-chemical composition-uses

AnionicAnionic detergents contain a negative ion (most commonly sulfate, SO42- or sulfonate SO3-)as the hydrophilic end of the molecule. The hydrocarbon chain contains a benzene ring at theends.

They are primarily used as cleaners for glass and ceramic dishes and clothing and are highlysudsing. This is due to the fact that these substances have negative surface charges, whichrepel the anionic detergents and can be easily washed away, carrying the emulsifiedgrease/dirt with it. They are usually combined with ionic detergents to provide enhancedstability.

CationicCationic detergents contain a positive ion (usually an ammonia compound). They emulsifyfats well, but are unsuitable for glass and ceramics as they contain negative surface charges.

They are commonly used as fabric softeners and hair conditioners because they reduce static,thus causing fabric and hair to appear ‘fluffy’. Other uses include germicides, mouthwash andantiseptic soaps owing to their germicidal properties.

Non-ionicNon-ionic detergents do not form ions in a solution at all. Instead, they contain hydrophilicgroups (such as oxygen atoms, alcohol groups or polysaccharides) along the hydrocarbonchain which form hydrogen bonds with water.

They are used for car-washing, cosmetics, dishwashing and froth flotation. One disadvantageis their loss of solubility in warm water.

_

+



solve problems and use available evidence to discuss, using examples, theenvironmental impacts of the use of soaps and detergents

BiodegradabilitySoaps consists of fatty acids and can therefore be decomposed by bacteria when it enterssewage or waterways. Therefore, it has no negative impact on the environment.

Early detergents were non-biodegradable as they were made from branched-chainhydrocarbons which are difficult for bacteria to decompose. This was alleviated in the 1970’swhen straight-chain hydrocarbon detergents were introduced.

The sulfonic acid group found in anionic detergents and non-ionic detergents are highlybiodegradable.

Presence of phosphatesThe main environmental impact of detergents was due to the addition of phosphates, as it wasdiscovered that they aided the effectiveness of detergents. The main problem with the use ofphosphates is their contribution to eutrophication in waterways.

Eco-friendly cleaning agentsEco-friendly cleaning agents use less non-essential chemical additives such as dyes andfragrances to reduce the toxicity of the detergent.

gather, process and present information from secondary sources to identify arange of fats and oils used for soap-making

Oil/fatOlive oil (oleic acid)

Palm oil (palmitic acid)Coconut oil (lauric, myristic acid)

Lard (palmitic, stearic, myristic acid)Tallow (palmitic, oleic, stearic)

Soybean oil (mainly polyunsaturated)Safflower oil (polyunsaturated)

Shea OilSunflower oilRice bran oil

Wheatgerm oil

O O

δ+ δ+

δ- δ-

O

http://hsc.csu.edu.au/chemistry/options/industrial/2764/Ch955.htm




Perform a first-hand investigation to carry out saponification and test theproduct

Experiment: Soap Production

Aim: to make soap by reacting a fat or oil and an alkali

Background: Soaps and other cleaning agents are often produced by the saponificationprocess. Soap making has been an important industry for many centuries. This reactioninvolves the adding of a caustic alkali solution to fats or oils. The ratio of alkali used to fat/oildepends upon the chemical make-up of the oil.

Materials:-beaker -olive oil-potassium hydroxide -boiling chips-boiling chips -electronic scales-stirring rod -mould-heating apparatus -universal indicator-universal indicator-hydrochloric acid

Precautions:Clean up any spillage and make sure the laboratory is wellventilated. There is a risk of spitting when the mixture is beingheated. Do not use the soap produced on your skin as there maybe excess KOH.

Method:1/ Accurately weight 10g of olive oil in a clean beaker.




2/ Calculate the mass of potassium hydroxide neededaccording to the equation given above.

3/ Add the potassium hydroxide to the olive oil.4/ Mix the reactants with a stirring rod.5/ Add boiling chips to the beaker and gently heat.6/ Continuously stir the reaction mixture while it isbeing heated.7/ When the soap has formed, wash it thoroughly to

remove any excess hydroxide.8/ Add 5 drops of universal indicator.9/ Add hydrochloric acid drop wise till the mixture is neutral.10/ Place into mould and place in incubator to dry the soap

Conclusion:What evidence suggests a reaction is occurring?Macroscopic changes such as the reaction mixture forming a stable, foamy emulsion.

Why was neutralisation necessary?To remove the excess hydroxide ions produced from the KOH used for the saponificationprocess



Perform a first-hand investigation to gather information and describe the propertiesof a named emulsion and relate these properties to its use.

Perform a first-hand investigation to demonstrate the effect of soap as an emulsifier

Experiment: The Emulsifying Power of Soaps and Detergents

Aim: -To examine the production of a soap/stain emulsion-To compare the emulsifying ability of various commercially available soaps and detergent.

Background:An emulsion is a mixture of two or more chemicals which under normal conditions would beimmiscible. Another chemical called an emulsifying agent is added to the immisciblechemicals and allows them to mix. Detergents and soaps act as emulsifying agents when weuse them to clean materials.

Materials:test tubestest tube rackolive oil or other suitable fat or oilrubber stoppers or corksa variety of commercially available soaps and detergents

Precautions:Clean up any spillage and make sure the laboratory is well ventilated. Be careful whenshaking not to spill any of the chemicals.

Method:Part A: Making an Emulsion1. Place 10 mL of tap water into two test tubes.2. Add 2 ml of oil to each test tube.3. Add a small amount of soap to one of the tubes.4. Place a rubber stopper or cork on each test tube and shake for 30 seconds.5. Place both test tubes in a rack and allow to stand.



Part B – Testing the Ability of Various Soaps and Detergents:1. Place 10ml of tap water into as many test tubes as you have soaps and detergents.2. Add 2mL of oil to each test tube.3. Add equal mass of different soaps to each one of the tubes. If liquid detergents are used,equal volumes should be used.4. Place a rubber stopper or cork on each test tube and shake for 30 seconds.5. Place both test tubes in a rack and allow to stand.6. Compare how long each mixture remains an emulsion by timing how long it takes toseparate into layers.

Conclusion and Discussion:What evidence suggests an emulsion has been produced?The oil and water formed a homogenous mixture with no distinct oil-water layers

What observations can be used to determine the emulsifying ability of the soaps anddetergents?The longer it takes for the emulsion to separate back into water and oil layers, the morepowerful its emulsifying ability

How could we gain a better idea as to which of the detergents and soaps were the bestemulsifiers?Repeat trials using a variety of different types of oils/fats, as well as varying the ratio of waterto oil used.

Why must equal masses or volumes of soaps and detergents be used in the experiment?To be able to compare the emulsifying abilities of different surfactants, it it necessary to useequal amounts of the surfactants



6. Solvay Process

Identify the raw materials used in the Solvay process and name the products

Raw materials are sodium chloride (from seawater), ammonia and Calcium carbonate(limestone). Products are sodium carbonate and calcium chloride (waste product).

The overall reaction:

Describe the uses of sodium carbonate

Uses of sodium carbonate:-manufacture of soap, glass, ceramics, paper, sodium hydroxide and sodium bicarbonate-petroleum refining-water softener (removes Mg2+ and Ca2+ ions)-pollution control (used to scrub exhaust gases to remove sulfur dioxide at power stations)-cheaper alternative to sodium hydroxide as a general base-cleaning agent in washing compounds

Identify, given a flow chart, the sequence of steps used in the Solvay process anddescribe the chemistry involved in:

-brine purification-hydrogen carbonate formation-formation of sodium carbonate-ammonia recovery

Brine PurificationSeawater is pumped into shallow ponds, where water is evaporated to leave behind a 30%concentrated brine. This is a mixture of magnesium and calcium salts, which must beremoved by precipitation.

Ca2+ ions are removed by adding Na2CO3:

Mg2+ ions are removed by adding NaOH:

A flocculent is added to allow the precipitate to be easily removed.

Hydrogen Carbonate FormationCrushed limestone is heated in a kiln to produce carbon dioxide and calcium oxide:





Coke (carbon) is also present in the kiln, producing more carbon dioxide when heated andproviding heat to decompose the lime:

The CaO is used in a later process. The purified brine from the previous step is added toammonia (NH4OH). The carbon dioxide from the limestone is bubbled through:

As chloride and sodium are spectator ions, the overall ionic equation:

Formation of Sodium carbonateThe ammonium chloride-sodium hydrogen carbonate solution is cooled to 0°C to precipitatethe sodium carbonate, as it is only slightly soluble at lower temperatures:

The mixture is filtered, dried and heated to ~300C to decompose it into sodium carbonate,water and carbon dioxide:

Ammonia RecoveryCalcium oxide from Hydrogen carbonate formation is dissolved in water to form calciumhydroxide:

When ammonium chloride from hydrogen carbonate formation is added, ammonia gas isliberated to be reused:

Discuss environmental issues associated with the Solvay process and explain howthese issues are addressed

Compared to previous methods, the Solvay process is less polluting as it reuses the productsammonia and carbon dioxide. However, some environmental issues remain.

Disposal of calcium chloride waste



Calcium chloride has few practical uses in vast quantities. When discharged into the ocean,there are no noticeable effects. However, when disposed of into rivers/waterways, it canincrease the chloride and calcium ion concentrations to such an extent that local ecosystemsare affected. In some areas, the calcium chloride is evaporated and placed in land-fill. Thisdoes not seem to have any effects, but future effects on water supplies are unknown.

Heat (thermal) pollutionAs the Solvay process is exothermicand the precipitation of NaHCO3 requires cooling.

This has traditionally been done by using river water as the coolant and simply dischargingthe hot water back into the waterway. This can have major effects on aquatic environments asoxygen is less soluble at higher temperatures.

Modern plants use air-cooling towers and recycle the water instead.

Solid wasteThe roasting of limestone in the kiln produces large amounts of silicates, clays as well asunburnt limestone. Traditionally, this waste was discharged into waterways where it causedproblems by forming a sludge. This waste may be used for bricks or simply as landfill.

Dust ControlDust is problematic and must be controlled by keeping vehicles in asphalt roadways, usingwetting solution to suppress dust in exposed areas, bag filters in the hydrogen carbonate plantand installation of dust scrubbing systems.

Noise suppressionNoise is reduced by enclosing noisy areas, using silencers to dampen noise and communitymonitoring to identify noise sources.

Perform a first-hand investigation to assess risk factors and then carry out achemical step involved in the Solvay process identifying any difficultiesassociated with the laboratory modelling of the step

Investigation: Sodium carbonate production

Aim: To model the production of sodium carbonate by the Solvay process

Materials:-Large beaker -sodium carbonate (Na2CO3) -Sintered glass filter -dilute ammonia (NH4OH)-dry ice/bottled CO2/CO2 from conc. HCl and CaCO3-Retort stand and ring -ice-Measuring cylinder -Bunsen burner-cork/stoppers-glass/rubber/plastic tubing



Safety: clean up any spillage and ensure good ventilation (ammonia solution is corrosive). Asgas is used, be careful of pressure accumulation. Dry ice ‘burns in contact with skin. Wearsafety glasses at all times.

Method:1/ Add sodium chloride to an ammonia solution until solution is saturated2/ Filter the solution to remove excess solid salt3/ Place ammonia/salt solution into measuring cylinder4/ Place marble chips into a conical flask, add concentrated HCl and use the tubing to

bubble CO2 into the ammonia-salt solution.

5/ Allow the gas to bubble through the solution, but monitor gas inlet as Sodiumhydrogen carbonate may block it

6/ Place the measuring cylinder into a large beaker and cool by filling with ice7/ Use sintered glass filter to filter sodium hydrogen carbonate that precipitates in flask8/ Place sodium hydrogen carbonate into a clean, dry test tube/crucible9/ Use Bunsen burner to gently heat the solid until water evaporates10/ Allow the product to cool

Results:

Measuring cylinder withammonia-salt solutionMarble chips and

concentratedHCl

Beaker with ice to aidprecipitation of

NaHCO3

Marble chips andconcentrated

HCl



Questions:

1. Write a balanced equation for the reaction

2. Explain why the gas inlet tube must be monitored

NaHCO3 may precipitate at the gas inlet and block it, thus causing an accumulation of CO2pressure in the flask containing acid and marble chips. As concentrated acid is used, this is apotential safety hazard.

3. Write a balanced equation for the conversion of the sodium hydrogen carbonate intosodium carbonate

4. Why must the sodium hydrogen carbonate be heated gently?Carbon dioxide gas is produced, which may cause the mixture to bubble violently

5. Calculate the yield of sodium hydrogen carbonate if 5g of salt was initially used in thereaction.

6. If 4.5 g of sodium chloride produced 0.9 g of solid sodium carbonate, calculate theefficiency of the reaction



Process information to solve problems and quantitatively analyse the relativequantities of reactants and products in each step of the process

Use available evidence to determine the criteria used to locate a chemicalindustry using the Solvay process as an example

Factors which influence the location of aSolvay plant

Example – The Solvay plant in Osborne, SA

Proximity to raw materials Osborne is located close to the coast. Thisallows easy access to sea water, which can bepumped into ponds for concentration andpurification.

The hot climate of Adelaide also helpsconcentrate the brine

A limestone deposit is ~50 km away, with a railline allowing a deposit each day

Proximity to market for product/transportlinks to market

Osborne has excellent rail, road and harbourconnections to supply sodium carbonate to glassmakers throughout Australia

Proximity to a population centre toprovide a labour force and the communityinfrastructure

Proximity to Adelaide means there is a reliableworkforce, schools and shops for workers

Proximity to site for waste disposal Previously discharged into Port river Now being used for landfill, brick manufacture



Solvay Process – Flow Chart

Purified Brine30% NaCl, H2O

Ammoniatedbrine

AmmoniaNH3(g)

Limestone

Lime Kiln Carbonating tower

Filter

Heat

Product Na2CO3(s)Sodium carbonate

Ammonia recovery

Waste productCaCl2

Lime Slaker

H2O CaO

industrial chemistry 2

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