Science 30Science 30Unit B: Chemistry and the Unit B: Chemistry and the

environmentenvironmentChapter 1: Acid DepositionChapter 1: Acid Deposition

1.1- Products of Combustion 1.1- Products of Combustion ReactionsReactions

Combustion reactions (eg. Cellular Combustion reactions (eg. Cellular respiration, burning fossil fuels) are useful respiration, burning fossil fuels) are useful but produce emissions.but produce emissions.

Collisions between the methane and Collisions between the methane and oxygen molecules form new molecules.oxygen molecules form new molecules.

If a hydrocarbon combusts, HIf a hydrocarbon combusts, H220 and CO0 and CO2 2

are formed; these are the waste products.are formed; these are the waste products.

Chemical Equations

a) Oxides of Carbona) Oxides of Carbon

Burning carbon compounds, or anything Burning carbon compounds, or anything with biomass, or hydrocarbons results in with biomass, or hydrocarbons results in carbon dioxide.carbon dioxide. Examples: C/R, volcanic eruptionsExamples: C/R, volcanic eruptions

Carbon dioxide is important in the carbon Carbon dioxide is important in the carbon cycle and as a greenhouse gas; cycle and as a greenhouse gas; contributes to climate change.contributes to climate change.

carbon cycle animation

Greenhouse effectGreenhouse effect

Greenhouse Effect - animated diagram

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Hole in the ozone layer

Carbon monoxideCarbon monoxide Carbon monoxide (CO) is produced when Carbon monoxide (CO) is produced when

the quantity of oxygen is limited in the quantity of oxygen is limited in combustion.combustion.

Caused by vehicle exhaust, furnaces (in Caused by vehicle exhaust, furnaces (in poor condition); natural concentration of poor condition); natural concentration of carbon monoxide in air is around 0.2 parts carbon monoxide in air is around 0.2 parts per million (ppm).per million (ppm).

Can bind to hemoglobin = decreased Can bind to hemoglobin = decreased amount of oxygen to tissues.amount of oxygen to tissues.

CO

b) Oxides of sulfurb) Oxides of sulfur Found when coal and crude oil or tar are Found when coal and crude oil or tar are

burnt; found in natural gas as sour gas burnt; found in natural gas as sour gas (hydrogen sulfide).(hydrogen sulfide).

Sour gas needs to have the hydrogen Sour gas needs to have the hydrogen sulfide removed.sulfide removed.

The amount of SOThe amount of SO22 released depends on released depends on the sulfur content of coal, normally 0.7% to the sulfur content of coal, normally 0.7% to 2% by weight. High sulfur coal sometimes 2% by weight. High sulfur coal sometimes contains as much as 6% sulfur by weight.contains as much as 6% sulfur by weight.

Air pollution reductionAir pollution reduction

Catalytic ConvertersCatalytic Converters Catalytic Converters againCatalytic Converters again Energy efficient homesEnergy efficient homes Reduce recycle reuseReduce recycle reuse

Air Pollution

flaringflaring

When low quality natural When low quality natural gas is produced, it is gas is produced, it is burned off to produce burned off to produce SOSO22 and SO and SO3 3 = flaring.= flaring.

Adds oxygen to Adds oxygen to hydrogen sulfide to form hydrogen sulfide to form products.products.

c) Oxides of Nitrogenc) Oxides of Nitrogen

Whenever any fuel is combusted, nitrogen Whenever any fuel is combusted, nitrogen is present (includes breathing).is present (includes breathing).

When temperature reaches 650When temperature reaches 650°C, °C, Nitrogen activates and forms NO and NONitrogen activates and forms NO and NO22..

These are referred to as NOThese are referred to as NOxx compounds. compounds. Common sources:Common sources:

Combustion of fuels in cars and furnaces.Combustion of fuels in cars and furnaces. Fossil fuel power plantsFossil fuel power plants

Fossil Fuels

d) Monitoring emissionsd) Monitoring emissions The government creates standards The government creates standards

to protect environment, organisms to protect environment, organisms and support sustainability of and support sustainability of resources.resources.

Monitored using specialized Monitored using specialized equipment and by an outside equipment and by an outside group.group.

Cars are monitored using MAML Cars are monitored using MAML labs.labs.

1.2) Acids and Bases1.2) Acids and Bases

Acids, Bases and Neutral solutions have Acids, Bases and Neutral solutions have specific properties that are used to classify specific properties that are used to classify them.them.

Acids: conducts a current (electrolyte), pH Acids: conducts a current (electrolyte), pH = 6 or less, corrosive, reacts with metals, = 6 or less, corrosive, reacts with metals, tastes sour.tastes sour.

Bases: Conducts current, corrosive, pH = 8 Bases: Conducts current, corrosive, pH = 8 or more, feels slippery, bitter.or more, feels slippery, bitter.

Neutrals: pH = 7, can be electrolytic or not.Neutrals: pH = 7, can be electrolytic or not.

There are 4 different types of solutions

Neutral molecular

Neutral ionic

Acid base

Solutions of compounds that are composed of non-metals only.

Solutions of compounds that are composed of metals combined with non-metals

Solutions of compounds that produce hydrogen ions.

Solutions of compounds that produce hydroxide ions

C12H22O11(aq) NaCl(aq) HCl(aq) KOH(aq)

CH3OH(aq) CaBr2(aq) H2SO4(aq) Mg(OH)2(aq

No effect on litmus

No effect on litmus

Turns litmus red

Turns litmus blue

a) Types of depositiona) Types of deposition 2 types of deposition:2 types of deposition:

Wet: emissions that Wet: emissions that contact precipitation and contact precipitation and return as rain/snow.return as rain/snow.

Dry: gases and particles Dry: gases and particles absorbed by the earth; absorbed by the earth; deposited on any deposited on any surface.surface.• Most deposition in Alberta Most deposition in Alberta

is from dry deposition.is from dry deposition.

b) Acidsb) Acids

Can be classified by properties (empirical) Can be classified by properties (empirical) or by chemical composition.or by chemical composition.

Classified as a molecular compound but Classified as a molecular compound but behave like ionic compounds when behave like ionic compounds when dissolved in water (electrolytic solutions).dissolved in water (electrolytic solutions).

The water molecules break the bonds in The water molecules break the bonds in ionic compounds; these charges can now ionic compounds; these charges can now move in a direction = conduct electricity.move in a direction = conduct electricity.

Electrostatic AttractionElectrostatic Attraction

Force that pulls oppositely charged objects Force that pulls oppositely charged objects towards each other.towards each other.

Water pulls positive ions towards oxygen; Water pulls positive ions towards oxygen; creates a positive and negative charge.creates a positive and negative charge.

Dissociation occurs when 2 ions separate Dissociation occurs when 2 ions separate into different charges.into different charges.

ArrheniusArrhenius

Svante Arrhenius formulated a theory in Svante Arrhenius formulated a theory in 1887 that all acids had a H+ ion and 1887 that all acids had a H+ ion and bases had an OH- ion.bases had an OH- ion.

Problems:Problems:1.1. Not all acids and bases have an H+ or OH-.Not all acids and bases have an H+ or OH-.2.2. H+ can not exist in water because it is so H+ can not exist in water because it is so

positively charged; actually forms Hpositively charged; actually forms H330 0 (hydronium ion) with a water particle.(hydronium ion) with a water particle.1.1. Hydronium ion is responsible for acidic properties.Hydronium ion is responsible for acidic properties.

c) Bronsted-Lowry Acid-base c) Bronsted-Lowry Acid-base reactionsreactions

Describes the actions of acids and bases Describes the actions of acids and bases during a chemical reaction.during a chemical reaction.

2 roles in the reaction:2 roles in the reaction: Donor (acid) = gives H+ (proton) ion.Donor (acid) = gives H+ (proton) ion. Acceptor (base) = accepts H+ (proton) ion.Acceptor (base) = accepts H+ (proton) ion.

Product is a conjugate acid/base.Product is a conjugate acid/base. Conjugate acid = formed when base accepts Conjugate acid = formed when base accepts

H+.H+. Conjugate base = formed when acid accepts Conjugate base = formed when acid accepts

H+.H+.

Writing reactionsWriting reactions

Loss of a H+ ion by acid = conjugate base.Loss of a H+ ion by acid = conjugate base. Recognized by no H+ ion in formula.Recognized by no H+ ion in formula.

Gain of H+ ion by base = conjugate acid.Gain of H+ ion by base = conjugate acid. Recognized by extra H+ ion in formula.Recognized by extra H+ ion in formula.

Use the table of acids and bases (page 12 Use the table of acids and bases (page 12 in data book) and follow 5 steps.in data book) and follow 5 steps.

Steps in Bronsted-Lowry reactionsSteps in Bronsted-Lowry reactions

Follow these 5 steps to write reaction:Follow these 5 steps to write reaction:1.1. Find the 2 solutions that are reacting.Find the 2 solutions that are reacting.2.2. Identify the acid and base.Identify the acid and base.

1.1. Stronger acid is higher on the table- always Stronger acid is higher on the table- always choose the highest one if both are listed!choose the highest one if both are listed!

2.2. The base is the non-acid (or weak acid).The base is the non-acid (or weak acid).

3.3. Write the reactants side of the equation.Write the reactants side of the equation.4.4. Find conjugate form of acid and base.Find conjugate form of acid and base.5.5. Write conjugate forms on products side of the Write conjugate forms on products side of the

equation.equation.

HCl

acid-base

EXAMPLE - Conjugate Acids: Write the formula for the conjugate acid of (a) F-, (b)NH3, (c) HSO4

-, and (d) CrO42-.

Solution:In each case, the formula for the conjugate acid is derived by adding one H+ ion to

the formulas above.a. HF b. NH4

+ c. H2SO4 d. HCrO4-

EXAMPLE - Conjugate Bases: Write the formula for the conjugate base of (a) HClO3, (b)H2SO3, (c) H2O, and (d) HCO3

-.Solution:In each case, the formula for the conjugate base is derived by removing one H+

ion from the formulas above.• ClO3

- b. HSO3

- c. OH- d. CO3

2-

See page 174 Example problem 1.2/1.3

Proton hoppingProton hopping

Confirmation of Bronsted-Lowry theory.Confirmation of Bronsted-Lowry theory. Used lasers to do this; captured images of Used lasers to do this; captured images of

motion in chemical reactions.motion in chemical reactions. Helped predict outcomes of acid-base Helped predict outcomes of acid-base

reactions.reactions.

d) Acid Depositiond) Acid Deposition

Emissions that are from human sources Emissions that are from human sources are are anthropogenic; anthropogenic; from combustion of from combustion of energy sources.energy sources.

These emissions combine with water to These emissions combine with water to form acid rain= acidic precipitation.form acid rain= acidic precipitation.

Rain is acidic due to natural and human Rain is acidic due to natural and human sources; the degree of acidity can be sources; the degree of acidity can be measured using pH.measured using pH.

e) pH and pH scalee) pH and pH scale pH is measuring the amount of hydronium pH is measuring the amount of hydronium

ions (Hions (H330+) in a solution.0+) in a solution. The number of Hydronium ions influences:The number of Hydronium ions influences:

Reactivity, amount of base needed to Reactivity, amount of base needed to neutralize/to react.neutralize/to react.

pH scale was developed in 1909 by pH scale was developed in 1909 by Sorenson; designed to measure dilute Sorenson; designed to measure dilute acids.acids.

pH scale measures from 1-14 (1-6 = acid, pH scale measures from 1-14 (1-6 = acid, 7= neutral, 8-14 = base).7= neutral, 8-14 = base).

pH

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pH calculationspH calculations

1909 - S1909 - SØØren Sørensen came up with “power ren Sørensen came up with “power of hydrogen” or pHof hydrogen” or pH

pH corresponds to the hydronium ion pH corresponds to the hydronium ion concentration in mol/Lconcentration in mol/L

[ H[ H33OO++(aq)(aq) ] = 10 ] = 10-pH-pH

pH = 5 then [ HpH = 5 then [ H33OO++(aq)(aq) ] = 10 ] = 10-5-5

[ H[ H33OO++(aq)(aq)] = 0.00001 ] = 0.00001 mol/Lmol/L or 1.0 x 10 or 1.0 x 10-5 -5 mol/Lmol/L

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pH to mol/L and back again …pH to mol/L and back again …

pH = - log [ HpH = - log [ H33OO++(aq)(aq) ] ]

[ H[ H33OO++(aq)(aq) ] = 10 ] = 10-pH-pH

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Converting pH to Converting pH to HH33OO++ concentration concentration

What is the concentration of hydrogen ions for an What is the concentration of hydrogen ions for an acid with a pH = 4.56?acid with a pH = 4.56?

You must take the inverse of a logYou must take the inverse of a log That is probably the 10x button on your calculatorThat is probably the 10x button on your calculator Type it in your calculator asType it in your calculator as 1010-4.56-4.56 = 0.000027542 mol/L = 0.000027542 mol/L 2.8 x 102.8 x 10-5-5 mol/L (sig digs) mol/L (sig digs) that is the concentration of hydrogen ionsthat is the concentration of hydrogen ions be sure to put the negative sign in before the 4.56be sure to put the negative sign in before the 4.56

Significant figures and pH/pOHSignificant figures and pH/pOH Calculate the pH of a solution where the [H+] is 0.00100 M.Calculate the pH of a solution where the [H+] is 0.00100 M. That's pretty easy, the answer is 3. After all 0.00100 is 10That's pretty easy, the answer is 3. After all 0.00100 is 10¯3¯3 and and

the negative log of 10the negative log of 10¯3¯3 is 3. is 3. But the pH is not written to reflect the number of significant But the pH is not written to reflect the number of significant

figures in the concentration.figures in the concentration. Notice that there are three sig figs in 0.00100 M.Notice that there are three sig figs in 0.00100 M. So, our pH value should also reflect three significant figures.So, our pH value should also reflect three significant figures. Let's phrase that another way: in a pH (and a pOH), the only Let's phrase that another way: in a pH (and a pOH), the only

place where significant figures are contained is in the decimal place where significant figures are contained is in the decimal portion.portion.

So, the correct answer to the above problem is 3.000. Three sig So, the correct answer to the above problem is 3.000. Three sig figs and they are all in the decimal portion, NOT (I repeat NOT) in figs and they are all in the decimal portion, NOT (I repeat NOT) in the whole number portion. the whole number portion.

Example ...Example ...

What is the pH of a solution with a [HWhat is the pH of a solution with a [H33OO++] ] of: of:

1.89 x 101.89 x 10-4 -4 mol/Lmol/L

AnswerAnswer pH = - log [1.89 x 10pH = - log [1.89 x 10-4-4] ] pH = 3.723 this is an acidic solution pH = 3.723 this is an acidic solution

because the pH is less than 7because the pH is less than 7

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PracticePractice

1 a) pH = 7.0

1 b) pH = 11.0

1 c) pH = 2.0

1 d) pH = 4.0

1 e) pH = 14.0

= 10-7 = 1 x 10-7 mol/L

= 10-11 = 1 x 10-11 mol/L

= 10-14 = 1 x 10-14 mol/L

= 10-2 = 1 x 10-2 mol/L

= 10-4 = 1 x 10-4 mol/L

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PracticePractice

2 a)[H3O+

(aq)] = 1.0 x 10-3 mol/L

2 b)[H3O+

(aq)] = 1.0 x 10-5 mol/L

2 c)[H3O+

(aq)] = 1.0 x 10-7 mol/L

2 d)[H3O+

(aq)] = 1.0 x 10-10 mol/L

pH = - log [ 10-3 ] = 3.00

pH = - log [ 10-5 ] = 5.00

pH = - log [ 10-7 ] = 7.00

pH = - log [ 10-10 ] = 10.00

Note: Answers have the correct amount of significant digits

f) Indicators First nations used natural acids to adjust the

color of the dyes made from leaves, berries and bark.

An indicator is anything that changes color in response to a change in pH.

Common indicators are shown in the table on page 12 of your booklet.

Used to measure the pH of a substance. pH meter is more accurate and gives exact

measure of pH.

The Rainbow Connection Demonstration

According to the acid-base indicator table, what is the color of each of the following indicators in the solutions of given pH?

(a) Phenolphthalein in a solution with a pH = 12.7.

(b) Bromothymol blue in a solution of pH = 2.8

(c) Methyl orange in a solution of pH = 3.

(d) Thymol blue in a pH = 5.0 solution

(e) Litmus in a solution with a pH of 8.2

Examples:

RED

YELLOW

RED

YELLOW

BLUE

Example Problem:

Separate samples of an unknown solution turned both methyl orange and bromothymol blue to yellow, and turned bromocresol green to blue. The pH of the unknown solution is likely __________

Example Problem:

methyl orange = yellow = 4.4+

bromothymol blue = yellow = 6.0-bromocresol green = blue = 5.4+The pH of the unknown solution is

likely between 5.4 and 6.0.

1.3) Impact of Acid Deposition

Higher levels of sulphates and nitrates in rainwater = higher concentration of hydronium ions and lower pH in water.

Wind patterns affect the deposition; provides way to trace pollution.

Alberta soil is slightly basic (alkaline) from the carbonate caused by erosion of limestone; neutralizes the acid deposition.

a) Buffering A buffer is used to resist pH change in soil or lake

water. The buffering capacity is the ability of a

substance to resistance pH change when an acid/base is added.

Specific plants need to be used in acidic soils; most are not able to grow due to lack of nutrients.

Nutrients are deposited in soil from biogeochemical cycles and through neutralization reactions.

b) pH and plants Plants absorb nutrients into the roots from

the soil, up to the leaves. Acid deposition changes nutrients so they

are insoluble; plants can not use them. Nutrient deficiencies causes plants to die

or become diseased. Chlorosis = calcium deficiency causes

decreased chlorophyll = yellow leaves. A neutral pH is best for plant growth; too

acidic or basic results in death.

c) Leaching acid in soil makes metal ions (aluminum and

mercury) available to plants. Plants take those nutrients into their roots and

they dissolve in the soil or groundwater = leaching.

Affects ecosystem by: Decreased root growth. Prevents absorption of calcium. Reduce decomposing soil bacteria. Mercury causes damage to gills. Methyl mercury traps in tissues = bioaccumulation

Biomagnification A pollutant increases in concentration up a

food chain. Causes disease and death.

Measured in ppm (106) or ppb (109) or ppt (1012)

d) Effect on Biotic factors

The abiotic (non-living) factors in an ecosystem affect the biotic (living).

Acid deposition decreases the biodiversity of the system.

Acid deposition affects the ecosystem in: Decreasing soil bacteria. Destroying waxy coating on plants. Damaging aquatic ecosystems.

1.4) Monitoring effects of acid deposition

Classification of acids is done in 2 ways: Quantitatively = involves measurement (pH,

titration) Qualitative = involves properties,

characteristics, attributes (color, observations)

a) Titrations

Used to determine the amount of acid/base present.

Uses an acid, base and an indicator. When the “end point” is reached, the

indicator will change color and the amount of acid/base needed to neutralize the solution is known.

Calculating the Concentration of Acids and Bases

Calculating concentrations: Calculate the concentration, in moles per litre, of 250 mL of a solution containing 0.243 mol of potassium hydroxide, KOH (s), used to analyze the concentration of an acid solution.

Given:n = .243 mol V= 250 mL (0.250 L)

Formula: C = n/V = 0.243 mol/0.250 L = 0.972 mol/L Answer: The KOH has a concentration of 0.972 mol/L The CONCENTRATION of an acid can easily be changed by

adding more solvent (water). What would the concentration of KOH be if an additional 150 mL

of water was added to the solution?

Technique Solution #1: “standard solution”

Will know the concentration and the volume used.

Solution #2: “unknown”Will know volume used but NOT the concentration

Acid / Base titrations will involve a NEUTRALIZATION Reaction

Neutralization Example:acid + base → salt + waterHCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

Titration Set-up

TITRANT solution with known

concentration goes in the buret

SAMPLE solution with

unknown concentration

goes in Erlenmeyer Flask

Titration Process The titrant will be added to sample drop by drop until

they have reacted fully (there is an equal amount of acid and base) and the ENDPOINT is reached.

How do you know you have reached the endpoint?The Erlenmeyer flask will also contain an INDICATOR that will change color when the reaction has reached the endpoint.

The indicator changes colour at the endpoint because the [H3O+] and therefore pH will have changed sufficiently.

How do you determine the volume of titrant used?

Read the volume of titrant in the buret before the titration begins AND once the endpoint has been reached

Subtract the volumes REMEMBER - read the bottom of the

meniscus!!

b) Acid Base Stoichiometry KOH(aq) + HCl(aq) KCl(aq) + HOH(aq)

Calculate ‘n’ for the given substance Use a molar ratio to calculate ‘n’ for the required

substance Make the appropriate calculation to answer the

question you are asked.

Calculate:Find the concentration of a solution of potassium hydroxide, KOH(aq), if it requires 8.32 mL of a 0.100 mol/L standard solution of hydrochloric acid to neutralize 10.0 mL of the potassium hydroxide solution.

HCl:HCl: C = n/V so, n = CVC = n/V so, n = CV n = (0.100 mol/L) (0.00832 L)n = (0.100 mol/L) (0.00832 L) n = 8.32 n = 8.32 xx 10 10-4-4 mol molNote: the balanced chemical equation is a 1 to Note: the balanced chemical equation is a 1 to

1 mole ratio, therefore n1 mole ratio, therefore nHClHCl = n = nKOHKOH

KOHKOH C = n/V = C = n/V = 8.32 8.32 xx 10 10-4-4 mol mol = = 0.0832 mol/L0.0832 mol/L

0.0100 L0.0100 L

Strong and Weak Acids and Bases

Strength ≠ Concentration Strength refers to the % of the acid or base that

dissociates in water You can change the concentration but you can

NOT change strength Strong acids and strong bases dissociate

completely in aqueous solutions Weak acids - only a portion of the acid

molecules release protons Weak base – only a portion of the base

molecules accept protons

Examples of Strong and Weak Acids / Bases

Example: NaOH is a strong base NaOH dissociates completely in H2O NaOH Na+ and OH-

Example: Acetic Acid is a weak acid Most acetic acid molecules DO NOT release protons

but instead remain in undissociated form

CH3COOH + H2O CH3COO- + H3O+

For every weak acid there is a conjugate base(See page 12 of Data Booklet)

What is the conjugate base of acetic acid?

c) Buffers A Buffer is a weak acid / weak base

conjugate pair Most effective when there are equal amount

of acid and base Example: H2CO3 in Blood

CO2 and H2O react to make H2CO3 (carbonic acid)

Carbonic acid resists changes in blood pH

H2CO3 + H2O → H3O+ + HCO3 -

Sources of buffering

Natural sources include hydrogen carbonate in your blood, levels of carbonate in the soil and limestone deposits.

Buffers do not work forever however; Eastern Canada has reached the capacity to buffer soil and has acidic deposition currently.