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Science 30. Unit B: Chemistry and the environment Chapter 1: Acid Deposition. 1.1- Products of Combustion Reactions. Combustion reactions (eg. Cellular respiration, burning fossil fuels) are useful but produce emissions. Collisions between the methane and oxygen molecules form new molecules.

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Science 30

Science 30

Unit B: Chemistry and the environment

Chapter 1: Acid Deposition


1 1 products of combustion reactions
1.1- Products of Combustion Reactions

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

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

  • If a hydrocarbon combusts, H20 and CO2 are formed; these are the waste products.



A oxides of carbon
a) Oxides of Carbon

  • Burning carbon compounds, or anything with biomass, or hydrocarbons results in carbon dioxide.

    • Examples: C/R, volcanic eruptions

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



Greenhouse effect
Greenhouse effect

Greenhouse Effect - animated diagram


7



Carbon monoxide
Carbon monoxide

  • Carbon monoxide (CO) is produced when the quantity of oxygen is limited in combustion.

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

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

CO


B oxides of sulfur
b) Oxides of sulfur

  • Found when coal and crude oil or tar are burnt; found in natural gas as sour gas (hydrogen sulfide).

  • Sour gas needs to have the hydrogen sulfide removed.

  • The amount of SO2 released depends on the sulfur content of coal, normally 0.7% to 2% by weight. High sulfur coal sometimes contains as much as 6% sulfur by weight.


Air pollution reduction
Air pollution reduction

Catalytic Converters

Catalytic Converters again

Energy efficient homes

Reduce recycle reuse

Air Pollution


Flaring
flaring

  • When low quality natural gas is produced, it is burned off to produce SO2 and SO3 = flaring.

  • Adds oxygen to hydrogen sulfide to form products.


C oxides of nitrogen
c) Oxides of Nitrogen

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

  • When temperature reaches 650°C, Nitrogen activates and forms NO and NO2.

  • These are referred to as NOx compounds.

  • Common sources:

    • Combustion of fuels in cars and furnaces.

    • Fossil fuel power plants

Fossil Fuels


D monitoring emissions
d) Monitoring emissions

  • The government creates standards to protect environment, organisms and support sustainability of resources.

  • Monitored using specialized equipment and by an outside group.

  • Cars are monitored using MAML labs.


1 2 acids and bases
1.2) Acids and Bases

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

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

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

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



A types of deposition
a) Types of deposition

  • 2 types of deposition:

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

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

      • Most deposition in Alberta is from dry deposition.


B acids
b) Acids

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

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

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


Electrostatic attraction
Electrostatic Attraction

  • Force that pulls oppositely charged objects towards each other.

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

  • Dissociation occurs when 2 ions separate into different charges.


Arrhenius
Arrhenius

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

  • Problems:

    • Not all acids and bases have an H+ or OH-.

    • H+ can not exist in water because it is so positively charged; actually forms H30 (hydronium ion) with a water particle.

      • Hydronium ion is responsible for acidic properties.


C bronsted lowry acid base reactions
c) Bronsted-Lowry Acid-base reactions

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

  • 2 roles in the reaction:

    • Donor (acid) = gives H+ (proton) ion.

    • Acceptor (base) = accepts H+ (proton) ion.

  • Product is a conjugate acid/base.

    • Conjugate acid = formed when base accepts H+.

    • Conjugate base = formed when acid accepts H+.


Writing reactions
Writing reactions

  • Loss of a H+ ion by acid = conjugate base.

    • Recognized by no H+ ion in formula.

  • Gain of H+ ion by base = conjugate acid.

    • Recognized by extra H+ ion in formula.

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


Steps in bronsted lowry reactions
Steps in Bronsted-Lowry reactions

  • Follow these 5 steps to write reaction:

    • Find the 2 solutions that are reacting.

    • Identify the acid and base.

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

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

    • Write the reactants side of the equation.

    • Find conjugate form of acid and base.

    • Write conjugate forms on products side of the 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. CO32-

See page 174 Example problem 1.2/1.3


Proton hopping
Proton hopping

  • Confirmation of Bronsted-Lowry theory.

  • Used lasers to do this; captured images of motion in chemical reactions.

  • Helped predict outcomes of acid-base reactions.


D acid deposition
d) Acid Deposition

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

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

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


E ph and ph scale
e) pH and pH scale

  • pH is measuring the amount of hydronium ions (H30+) in a solution.

  • The number of Hydronium ions influences:

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

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

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



Ph calculations
pH calculations

  • 1909 - SØren Sørensen came up with “power of hydrogen” or pH

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

  • [ H3O+(aq) ] = 10-pH

  • pH = 5 then [ H3O+(aq) ] = 10-5

  • [ H3O+(aq)] = 0.00001 mol/L or 1.0 x 10-5 mol/L


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

  • pH = - log [ H3O+(aq) ]

  • [ H3O+(aq) ] = 10-pH


Converting ph to h 3 o concentration
Converting pH to H3O+ concentration

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

  • You must take the inverse of a log

  • That is probably the 10x button on your calculator

  • Type it in your calculator as

  • 10-4.56 = 0.000027542 mol/L

  • 2.8 x 10-5 mol/L (sig digs)

  • that is the concentration of hydrogen ions

  • be sure to put the negative sign in before the 4.56


Significant figures and ph poh
Significant figures and pH/pOH

  • 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 10¯3 and the negative log of 10¯3 is 3.

  • But the pH is not written to reflect the number of significant figures in the concentration.

  • Notice that there are three sig figs in 0.00100 M.

  • So, our pH value should also reflect three significant figures.

  • Let's phrase that another way: in a pH (and a pOH), the only place where significant figures are contained is in the decimal portion.

  • 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 the whole number portion.


Example
Example ...

  • What is the pH of a solution with a [H3O+] of:

    1.89 x 10-4 mol/L

    Answer

  • pH = - log [1.89 x 10-4]

  • pH = 3.723 this is an acidic solution because the pH is less than 7


Practice
Practice

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

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

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

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

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


Practice1
Practice

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
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.



Examples
Examples:

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

RED

YELLOW

RED

YELLOW

BLUE


Example problem
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 problem1
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
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) 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
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
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
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
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
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
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 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 CONCENTRATIONof 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
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 + water

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)


Titration set up
Titration Set-up

TITRANT

solution with known concentration

goes in the buret

  • SAMPLE

  • solution with unknown concentration

  • goes in Erlenmeyer Flask


Titration process
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
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
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:

    • C = n/V so, n = CV

    • n = (0.100 mol/L) (0.00832 L)

    • n = 8.32 x 10-4 mol

      Note: the balanced chemical equation is a 1 to 1 mole ratio, therefore nHCl = nKOH

  • KOH

    • C = n/V = 8.32 x 10-4 mol = 0.0832 mol/L 0.0100 L


Strong and weak acids and bases
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
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
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
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.


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