C3 Revision

C3.1 Water Testing • Qualitative Analysis is where you find out what type of

substance you have present.

• Quantitative Analysis is when you deduce the amount of unknown sample you have.

• Water samples contain IONIC COMPOUNDS which contain both CATIONS (positive) and ANIONS (negative ions).

• Ion tests must only give a positive result or one type of ion.

C3.1 Water Testing • Flame tests are commonly used

for CATION (metals).

• Precipitate reactions can also be used by reaction the ionic solution with SODIUM HYDROXIDE as most metal hydroxides are insoluble in water.

Questions • 1-Describe a Qualitative Analysis. • 2-Describe a Quantitative Analysis. • 3-Name 2 Ionic compounds contained in water • 4-Flame tests are commonly used to test what type of ion? • 5-What chemical is used for precipitation reaction? • 6-Copy and complete the table

Cations Symbol Precipitate

Aluminium

calcium

Iron (II)

Iron (III)

C3.2 Safe Water • Testing for the Halogens

• This is performed by acidifying the sample with dilute Nitric Acid and then reacting with Silver Nitrate to form a precipitate. • This reaction works by the Halogen displacing the Nitrate in Silver

Nitrate with the Halogen. • Testing for Ammonium ions (NH4

+) • Warm the solution to release the Ammonium ions as a vapour • It will turn damp red litmus paper blue.

C3.3 Ion Identification • Imagine you have been given an unknown sample…how can

you test for the different Ions.

• 1) • 2) • 3) • 4)

C3.4 Safe Limits • Ion identification is used in many different industries. For

example: • Water Industry to test for dissolved ions (both Halogens and

other ions such as aluminium (linked to Alzheimer's disease). • Blood testing to test for different ions (Iron linked to Anaemia,

Sodium linked to kidney function).

C3.5 Water Solutes Types of Water

• Soft water – contains low levels of ions (Na, Mg) – easily

produces a lather • Hard water – contains lots of dissolved ions (Ca, Mg) –

produced scum not lather – used lots of soap for cleaning • Permanently hard water – cannot be easily softened • Temporarily hard water – can be softened by boiling.

C3.5 Water Solutes Calculating Concentration

• Concentrations of ions are calculated generally in mgdm-3 or

gdm-3. • 1dm3 is equal to 1000cm3 (1 litre) • To calculate concentration use the following formula:

Questions • Define the following terms:

• Soft water

• Hard water

• Concentration

• Name two ions that can cause water to be hard.

C3.6 Hard and Soft Water Temporarily hard water

• This water is softened by boiling. It converts the Calcium Hydrogen carbonate into insoluble Calcium Carbonate (lime scale).

• Softening the water improves its ability to form a lather and therefore reduce the amount of soap required.

C3.6 Hard and Soft Water Softening Permanently hard

water

• This can be performed using ION EXCHANGE. This involves Sodium ions (Na+) in the resin displacing Calcium (Ca2+) and Magnesium (Mg2+) in the water sample and softening it.

Questions • Describe the difference between permanent hard water and

temporary hard water.

• Why does ion exchange soften all types of water, while boiling water removes only temporary hardness?

• State a method that can be used to soften all types of hard water. Explain how it works.

C3.8 Particles and Moles • Substances can be measured in several ways. They can be:

• Number of grams • Number of particles • Number of moles

• One mole of atoms is equal to the AVEGADRO number of particles (6.02X1023)

• The mass of one mole of atoms is equal to the Relative Atomic Mass number (top number on periodic table).

Questions • Calculate relative molecular mass of the following

compounds: • CuSO4

• CaCO3

• Calculate the number of moles of: • Calcium atoms in 80g of calcium • Sulphur dioxide molecules in 6.4g of SO2

C3.8 Particles and Moles • To calculate the number of moles use the following formulas:

C3.9 Preparing Soluble Salts Making Copper Sulphate

from Copper Oxide

1. React excess oxide (insoluble) with accurate volume acid.

2. Filter excess copper oxide and collect copper sulphate solution.

3. Evaporate solvent (water) to crystallise the salt.

C3.9 Preparing Soluble Salts Titrations

(preparing a salt from two soluble reactants)

• These reactions are NEUTRALISATION REACTIONS.

• It involves accurately calculating the volume of ACID required to neutralise the BASE.

• An INDICATOR is used to deduce the point of NEUTRALISATION (end point).

• A pipette is used to measure the base accurately.

• A burette is used to add the acid accurately. • One the correct volumes have been obtained

then the reaction is performed without the indicator

Titration Calculations • Step 1-Calculate the number of moles for the given substance.

• Step 2- Use balanced equation to calculate the number of

moles needed for acid or base.

• Step 3-Calculate concentration of the solution. Concentration of a solution = Number of moles of solute [mol] / Volume of solution

Question • 25.00cm3 of NaOH solution was titrated against 0.10 mol/dm3

HCl. An average of 20.00cm3 of the acid was needed to react completely. What is the concentration of the NaOH ?

Answer- Page 126/Extended book

C3.13 Electrolysis • Electrolysis can only happen when IONIC substances are

either DISSOLVED or MOLTEN. • Sodium metal is produced through the electrolysis of MOLTEN

Sodium Chloride.

C3.13 Electrolysis • Oxidation is the loss of electrons and happens at the ANODE. • Reduction is the gain of electrons and happens at the CATHODE.

• Sodium metal is used in street lights as it gives out a yellow coloured light. • Liquid Sodium is used as a coolant in Nuclear Reactors as it has a high

THERMAL CONDUCTIVITY.

C3.15 Electrolysis of Salts • Electrolysis of salts in solution

• This involves both the electrolysis of the salt and the electrolysis of water.

• The salt splits into its two component ions. • The water splits into Hydrogen ions (H+) and Hydroxide

Ions (OH-). • To perform electrolysis you must have INERT

(unreactive) electrodes as some of the products can be highly corrosive.

Questions Write the half equations for the electrolysis of Lead Bromide.

Write the symbol and charge for a hydrogen Ion. Write the symbol and charge for a Hydroxide Ion. Name the 4 aqueous ions in salt water. What is the overall equation for the electrolysis of Sodium chloride? And the half equations?

Electrolysis of Sodium Chloride Solution

C3.17 Uses of Electrolysis • Purification of Copper • An electrode of impure copper is used as the ANODE. • Pure copper is used as the CATHODE. • The electrolyte is Copper Sulphate solution.

Questions Name the type of copper used at the anode. Name the type of copper used at the cathode. Name the electrolyte in the purification of copper. State the half equations for the purification of copper.

C3.17 Uses of Electrolysis • Electroplating • Electroplating is when a thin coat of valuable (or unreactive) metal

is applied to a cheaper (more reactive) metal. • Silver and Gold are metals that are commonly used for

electroplating.

C3.18 Molar Volume of Gases • 1 mole of = 24dm3 (at room temperature and a gas atmospheric pressure)

A GAS SYRINGE is used to collect gases during reactions to allow molar gas calculations to

be performed

Questions • Define the term yield?

• Work out the number of moles: • 30g of Na

• 35g of NaCl

• 50g of H2O

C3.19 Fertilisers and the Haber Process • Nitrogenous fertilisers (ones that contain Nitrogen) are

manufactured from AMMONIA. These fertilisers are used to promote plant growth. These fertilisers increase the yield of crops that are produced.

• If these fertilisers are used excessively then this can lead to run off into rivers and lakes (or any other water source). This results in excessive plant growth (EUTROPHICATION). When these plants die they decompose by bacteria which uses up the OXYGEN.

C3.19 Fertilisers and the Haber Process

• The HABER process is a REVERSIBLE reaction which will reach DYNAMIC EQUILLIBRIUM.

• Dynamic equilibrium is where the FORWARDS and BACKWARDS reactions are happening at the same rate.

Questions • Explain Eutrophication.

• Is the Haber process reversible?

• Define the term Dynamic equilibrium (Haber Process).

• State the balanced symbol equation for the Haber process.

C3.20 The Haber process

• When AMMONIA is formed it releases heat (EXOTHERMIC). This is the FORWARDS reaction.

• The reverse reaction will be the opposite which makes it ENDOTHERMIC (takes in heat)

• When DYNAMIC EQUILLIBRIUM is reached these two reactions occur at the SAME RATE.

• Adjusting the temperature and pressure will affect the position of the equilibrium, favour the PRODUCT or REACTANT.

C3.20 The Haber process N2 + 3 H2 ⇌ 2 NH3

• Reactant = 4 molecules • Products = 2 molecules

Pressure and the Haber process • If you increased the pressure of the reaction the equilibrium would favour

the PRODUCTS (move to the right). This is because the particles are being forced closer together and therefore more likely to react.

Temperature and the Haber process • As the reaction is EXOTHERMIC it favours cooler conditions (it releases

energy into the surrounding environment). • An increase in temperature would move the equilibrium to the left (favour

the reactants). • A low temperature would increase the yield but slow the rate of reaction.

C3.20 The Haber process • Optimal conditions are used to ensure that the maximum possible yield is

produced safely and at a sufficient rate to be economically viable.

• Temperature – approx. 450OC • Pressure – 200atm (200 times atmospheric) • Catalyst – Iron catalyst

• A catalyst increases the rate of reaction without ever being used in the

reaction. It works by lowering the activation energy for the reaction (energy required for a successful collision)

• If the temperature or pressure is too high then there can be safety implications and too low will result in a lower yield.

Questions • Explain how pressure affects the yield in the Haber process.

• Explain how a high and a low temperature affect the yield of

ammonia.

• State the temperature of the Haber process.

• State the atmospheres needed for the Haber process.

• Name the catalyst used.

• Explain the role of a catalyst.

C3.21 Fermentation • Ethanol (alcohol) can be produced by the fermentation of

CARBOHYDRATES (sugars). • Fermentation occurs when YEAST convert sugars into alcohol. The

yeast act as an ENZYME.

• For this to happen successfully the following conditions must be sustained: • Kept warm (allow the bacteria to work successfully, too hot will kill

them) • Anaerobic conditions (no oxygen)

Questions State the balanced symbol equation for fermentation. • Explain how alcohol is made through fermentation.

• State the two conditions needed for fermentation to occur. • 1-

• 2-

C3.22 Alcoholic Drinks • Different types of alcoholic drink contain different percentages of

ethanol. The higher the alcohol content the higher % it is given. • 1 unit of alcohol = 10cm3 pure ethanol • The effects of alcohol are:

• Slower reaction times • Violent/aggressive behaviour • Loss of balance/coordination • Vomiting and fainting • Dehydration

• Prolonged alcohol consumption can result in an increased risk of HEART DISEASE, STROKE or LIVER CIRROHISIS.

• Alcoholic spirits are made by FRACTINAL DISTILLATION where the ethanol is removed first and the water is left behind (increasing the alcoholic content)

C3.23 Ethanol production Ethanol can be produced in two main ways:

1. Fermentation – sugars are turned into ethanol and carbon dioxide through the anaerobic respiration of YEAST. 2. Hydration of Ethene (crude oil fraction) – reacting ethene with steam in the presence of a catalyst (addition reaction)

C3.23 Ethanol production • Each method of Ethanol production has both social, environmental

and economical advantages and disadvantages. • This information needs to be evaluated to determine the best

method of production for individual cases.

Making Ethene • Ethene can be made by the cracking of CRUDE OIL but also the

DEHYDRATION of Ethanol.

Questions

• State 3 effects of alcohol on the body. • 1- • 2- • 3-

• Explain the hydration of Ethene.

• State the symbol equation for the production of ethane using

steam.

C3.24 Homologous series

• Alkanes – a hydrocarbon containing only

C-C bonds. • Alkenes – a hydrocarbon

containing at least one C=C bond.

• Alcohol – a hydrocarbon containing at least one –O-H group.

A HOMOLOGOUS series is a series of compounds that have the same general formula and similar chemical properties but have variation in boiling points.

Questions • Define the term homologous.

• Describe the type of bonds in an alkane.

• Describe the bonds in an alkene.

• State the group found in alcohols.

C3.25 Ethanoic acid • Ethanoic acid is a CARBOXYLIC ACID. • It is the active ingredient in VINEGAR. • It is produced by the OXIDATION of ethanol (under aerobic conditions). • It has a sharp, sour taste and can be used as a PRESERVATIVE. • Ethanoic acid reacts with metals to form salts (ending – ethanoate). • Carboxylic acids react in the same way as normal acids. They are classified

as weak acids. • Carboxylic acids are named in the same way as other homologous series.

Their ending is –anoic acid. • Their functional group is –COOH.

C3.26 Esters • Esters are made during the reaction of ALCOHOLS and CARBOXYLIC

ACIDS. • They are commonly used as FLAVOURINGS and FRAGRANCES as they have

distinctive smells and tastes. • Ethanol reacts with ethanoic acid to from the ester ETHYL ETHANOATE.

• Esters can also be turned into FIBRES to make FABRICS – POLYESTER. • Polyesters can be recycled to form FLEECE.

Questions • Draw the molecular structure for the production of an ester

and write the word equation underneath.

• Name two substances react to form an ester.

• Give two used for esters.

• Ethanol reacts with ethanoic acid to from which ester?

C3.27 Fats, Oils and Soaps • Fats and Oils are big esters. The only difference is fats are SOLID at room

temperature where as oils are LIQUID. • Soaps can be made from fats and oils by heating with a concentrated

alkali.

• Oils are commonly UNSATURATED (contain C=C bonds). • Fats are SATURATED (contain C-C bonds). • To turn an oil into a fat you must HYDROGENATE it (addition of Hydrogen)

C3.27 Fats, Oils and Soaps • How do Soaps work? • A soap can be shown as a tadpole shape

– head is water loving (HYROPHILLIC) and tail is water hating (HYDROPHOBIC).

• The head has a negatively charged oxygen ion (anion).

• The tail is a hydrocarbon (water hating) • Hydrophobic tail sticks into grease. • Hydrophilic end sticks out to attract

water. • Grease particle surrounded by

hydrophilic heads. • Removed by water attraction (grease can

now mix with water)

Questions • State the word equation to form a soap from fats.

• Are Oils saturated or unsaturated? • What type of double bond do fats contain?

• How an oil can be turned into margarine?

• Define the term hydrophobic. • Define the term hydrophilic. • Explain how soaps work (6 bullet points)