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Science 30

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

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  1. Science 30 Unit B: Chemistry and the environment Chapter 1: Acid Deposition

  2. 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.

  3. Chemical Equations

  4. 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.

  5. carbon cycle animation

  6. Greenhouse effect Greenhouse Effect - animated diagram

  7. 7

  8. Hole in the ozone layer

  9. 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

  10. 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.

  11. Air pollution reduction Catalytic Converters Catalytic Converters again Energy efficient homes Reduce recycle reuse Air Pollution

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. There are 4 different types of solutions

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  21. 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+.

  22. 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.

  23. 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.

  24. HCl acid-base

  25. 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

  26. 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.

  27. 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.

  28. 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).

  29. pH

  30. 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

  31. pH to mol/L and back again … • pH = - log [ H3O+(aq) ] • [ H3O+(aq) ] = 10-pH

  32. 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 figs) • that is the concentration of hydrogen ions • be sure to put the negative sign in before the 4.56

  33. 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.

  34. 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

  35. 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

  36. Practice pH = - log [ 10-3 ] = 3 pH = - log [ 10-5 ] = 5 pH = - log [ 10-7 ] = 7 pH = - log [ 10-10 ] = 10

  37. 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.

  38. The Rainbow Connection Demonstration

  39. 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

  40. 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 __________

  41. 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.

  42. 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.

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