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UNIT B Environmental Chemistry

UNIT B Environmental Chemistry. Acids and bases and their effects on the environment Organic compounds and their effects on the environment Risks and benefits of using chemical processes and assessing technologies for reducing the chemical impact on the environment. Outcome 1: Acids & Bases.

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UNIT B Environmental Chemistry

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  1. UNIT B Environmental Chemistry Acids and bases and their effects on the environment Organic compounds and their effects on the environment Risks and benefits of using chemical processes and assessing technologies for reducing the chemical impact on the environment

  2. Outcome 1: Acids & Bases SPECIFIC OUTCOMES • B1.1 Define acids and bases • B1.2 Diagnostic tests for acids (weak & strong), bases (weak & strong), neutral ionic & neutral molecular (pH meter, pH paper, indicators, reactions…) • B1.3 Relationship between pH and hydronium concentration (increase 1 = decrease of 10) • pH = -log [H3O+]; • [H3O+] = invlog (-pH) • B1.6 Indicators (include historical perspective) • B1.8 & B1.9 Sources and environmental impact of acid deposition (CO2, SO2, NOx) • B1.4, B1.5 & B1.7Buffers & buffering capacity (maintaining a pH in a living system) • B1.2 Skill: Titrations (CacidVacid = CbaseVbase) • B3.2 Solutions to Acid Deposition

  3. Outcome 2:Organic compounds • B2.1: Identify & name organic compound with one functional group (halids, alcohols, carboxylic acids & esters) • B2.2: Describe come uses for organic compounds listed in B2.1 • B2.3: Identify common organic pollutants (hydrocarbons, waste, CFCs, PCBs, dixons & furans, DDT, CO2, POP) • B2.4: List source and hazards of halids and benzene compounds • B2.5: Explain what causes smog, ozone depletion, and organic pollution • B2.6: Explain biomagnification

  4. Outcome 3: Chemical processes & technologies • B3.1: Risks and benefits of chemical processes that may harm the environment • B3.2: Chemical technologies that reduce production and emission of harmful chemicals (scrubbers, catalytic convertors, etc…) • B3.3: Alternatives to chemicals (biomediation, biological controls, biodegradable products, etc…) • B3.1 SKILL: Interpret data from water tests (pH, BOD, dissolved oxygen, etc…)

  5. Unit B Lessons Lesson 1.1: Products of Combustion Lesson 1.2: Acids & Bases Lesson 1.3: Quantifying Acids Lesson 1.4: Impact of Acid Deposition Lesson 1.5: Learning from Acid Rain Lesson 2.1: Organic Chemistry Lesson 2.2: Alcohols, Acids & Esters Lesson 2.3: Understanding Exposure

  6. Lesson 1.1: Products of Combustion (see lesson 1.3)Lesson 1.2 Acids & Bases

  7. Review of compounds • Ionic compound: a compound composed of charged parts, often a metal and a non-metal atom; usually conducts when dissolved (electrolytes) • Molecular compound: a compound composed of two or more non-metals; may dissolve in water; usually non-conductive (non-electrolytes) • Acid: a corrosive compound composed of hydrogen ions; always conducts (electrolyte) • Base: a caustic compound composed of hydroxide ions and an alkali or alkaline metal; always conducts (electrolyte)

  8. Review of Diagnostic tests

  9. Review of Diagnostic Tests Cont.

  10. Names and uses for acids and bases were established long before their physical nature or the reasons for their characteristic properties were understood. • Acids were originally recognized by their sour taste. The word acid is derived from the Latin word acetum. • Bases were substances that were usually soapy to the touch and that reacted with acids to form salt. • Antoine Lavoisier was a French chemist who first used the word "oxygen," from the Greek meaning "acid-former," to describe the component of air that he thought was the acidifying agent in reactions. We still call the gas oxygen even through his hypothesiswas wrong. Review Acids and Base History (Extra)

  11. Review Skill: Storage, Handling, & Disposal • Acids and bases are both dangerous because they are reactive, and can burn skin and eyes. This is called corrosive in acids. In bases this property is called caustic. • Acids and bases should have WHMIS labels and be stored in a cool dry place out of the reach of children. • Strong acid spills should be neutralized with a weak base (baking soda) and a strong base spill should be neutralized with a weak acid (vinegar). • Always add acids to water (A&W) to prevent splashing

  12. Review of compounds & Ions involved

  13. Review of special properties of water (H2O(l) ) • Water reactions: H2O(l)= HOH • HOH  H+ (aq) + OH- (aq) • H2O(l)+ H2O(l) H3O+(aq) + OH- (aq) • Water is neutral when mixed with neutral substances like sodium chloride (NaCl) or sugar (C12H22O11). • Water is a acid when it donates a hydrogen to a strong base like sodium hydroxide (NaOH). • Water is a base when it accepts a hydrogen (becomes hydronium) from a strong acid like hydrogen chloride (HCl).

  14. B1.1 What is the definition of an acid, base & neutral compound? • Arrhenius’s definition (sand) • Acids form aqueous solutions that contain hydrogen ion (H+(aq)) ie) HCl(aq) H+(aq)+Cl-(aq) • Bases form aqueous solutions that contain hydroxide ion (OH-(aq)) ie) NaOH(aq)Na++OH - • Neutral compounds do not contain hydrogen and hydroxide ion. Ie) NaCl • Bronstead & Lowry’s definition (rock) • Acids donate a proton or hydrogen ion (H+(aq)) • Bases accept a proton or hydrogen ion (H+(aq)) • A Neutral substance does not donate or accept hydrogen ions. (H+(aq))

  15. B1.2 Properties of Acids & bases Bases • Taste bitter • Feel slippery • Turn red litmus blue • Bromothymol blue stays blue • Turn phenolphthalein pink • Have a pH greater than 7 • Reacts with animal fat to make soap • Neutralize acids Acids • Taste sour • Feels like water • Turn blue litmus red • Bromothymol Blue turns yellow • Phenolphthalein stays colorless • Have a pH of less than 7 • React with metal to produce H2 gas • Neutralize bases

  16. B1.2 What is a strong acid, weak acid, strong base & weak base • A strong acid is an acid that completely donates ALL its hydrogen. • A weak acid is an acid that DOES NOT completely donate its hydrogen • A strong base is a base that accepts ALL the hydrogens that are available • A weak base is a base that DOES NOT completely accept all the hydrogen available

  17. Label the following on the acid table on page 12 Strong acids pH = 1 Salts pH=7 Weak Bases weaker Weaker Weak Acids vinegar Bakingsoda Strong Base pH=14 pH = 7 (less conductive)

  18. B1.2 Acid-Base reactions • The strongest acid will always react with the strongest base. • The products of an acid-base reaction are: • Conjugate acid: an acid formed when a base accepts a hydrogen • Conjugate base: a base formed when an acid donates a hydrogen HCl + H2O H3O+ + Cl- AcidBase conjugate comjugate acidbase Acid base pairs

  19. B1.2 How to write acid-base reactions • Locate the reactants on the table of acids & bases • Identify the strongest acid & strongest base • Write the reactants (include states) • Identify the conjugate acid and base and write them as products. (include states)

  20. B1.2 Acid-base reaction example: sour gas(H2S) reacts with water. • Locate H2S & H2O • H2S is the stronger acid (higher); H2O is the base (the other H2O is a weak acid) • Write the reactants: • Identify the conjugate acid & base and write as products: Acid base H2S(aq) + H2O(l)  H3O+(aq) + HS-(aq) conj acid conj base

  21. B1.2 More Acid Base reactions. • Acid Base reactions - Generic acid: HX(aq) + H2O (l)H3O+(aq)+X-(aq) Example: HCl(aq) + H2O (l)H3O+(aq)+ Cl-(aq) Acid Base Acid Base The arrows identify the acid-base pairs • Acid base reactions with a spectator (S = spectator) Generic base: S X+ HOH  S+ + OH- + HX Example: NaF + HOH  Na+ + OH- + HF Base Acid Base Acid

  22. B1.3 Definitions of pH • pH stands for power of Hydrogen • pH is a value that represents the how acidic a solution is. • pH is the negative log of the hydronium concentration. (pH = -log [H3O+]) • pH calculations are used to determine the exponent of the hydronium (H3O+) concentration without the negative.

  23. B1.3 Concentration & pH • The pH and the exponent are the same • As pH increases by 1.0, the hydronium concentration decreases by 10

  24. B1.3 pH Illustration NOTE: [ ] means mol/L Beaker # 1Beaker # 2 Beaker # 3 pH = 1.0pH = 2.0 pH = 3.0 [1 x 10-1][1 x 10-2] [1 x 10-3] 1/10 1/100

  25. B1.3 Calculating pH with the TI 83 & pH formula on pg 11 of your databook • Determine the pH of a sample of rainwater that has a hydronium-ion concentration, [H3O+(aq)], of 1.00 x 10-4 mol/L. Solution pH=-log10[H3O+(aq)] = -log10[1.00x 10-4] = 4.000 (3 sig digs; no units)

  26. B1.3 Calculating [H3O+] in the TI 83 using the formula on pg 11 • Calculate the hydronium-ion concentration, [H3O+(aq)] in a shampoo with a pH of 5.72. [H3O+(aq)] = 10-pH = 10 -5.722 significant digits = 1.905…x 10-6 mol/L = 1.9 x 10-6 mol/L 2 signficant digits

  27. B1.6 Indicator definition • An indicator is a weak acid or conjugate base that changes color with a change in pH. • Indicators exist in their weak acid form (can donate a proton) or in its conjugate base form (can receive a proton). • The Blackfoot First Nations used natural occurring indicators to change the color of their dyes.

  28. B1.6 Information on Indicators from the databook (pg 12) • NAME: bromothymol blue • ABBREVIATION: HBb(aq)/Bb-(aq) • pH RANGE: the pH where the indicator changes color. HBb range is 6.0to7.6 • 3 COLOURS: • a pH below 6.0 will be yellow; • between 6.0 and 7.6 the solution will be green (yellow + blue); • above 7.6 the solution will be blue.

  29. B1.6 Indicators in combination to estimate the pH What is the pH range if bromothymol blue is blue, phenolphthalein is colorless and phenol red is red? • HBb is blue; pH is above 7.6 (pH > 7.6) • HPh is colorless; pH is less than 8.2 (pH < 8.2) • Phenol red is red; pH is above 8.0 (pH > 8.0)

  30. B1.6 Using pH meters for accurate pH measurements • A pH meter contains a probe that detects the concentration of hydronium ions in solution to the hundredth or thousandth of a pH unit

  31. Lesson 1.3 Impact of Acid Deposition 5) Acid Deposition: Wet & dry forms of acids that are deposited on land and water. The main gases responsible are CO2, NOx & SOx

  32. B1.8 Combustion reactions create CO2 & CO • Oil, Methane (natural gas; CH4) & coal are plentiful hydrocarbon (made of H & C) fuels used to run engines, heat our homes and produce electricity. • Combustion reactions produce excess carbon dioxide (CO2) which traps atmospheric heat (global warming) influencing climate change. It also creates normal rain. • With limited oxygen, combustion reactions produce carbon monoxide (CO) which is a toxic gas (attaches to the hemoglobin preventing oxygen from attaching)

  33. B1.8 Balancing Combustion Reactions • What happens to the hydrocarbon? CxHy + (2X + y/2)/2 O2(g)X CO2(g)+ y/2 H2O(g) • Balance the carbon atoms by placing the subscript X in front of the CO2 • Balance the hydrogen atoms by placing Y/2 in front of the H2O • Balance the oxygen atoms by adding all the oxygens on the product side and dividing by 2. NOTE: For more complex reactions subtract the oxygen in the hydrocarbon before dividing by 2

  34. B1.8 Other reactions producing CO2

  35. B1.8 Combustion reactions that create sulphur oxides (SO2) Sour Gas flare • Sulfur containing fuels like coal crude oil, tar sands, and natural gas are used in industry, electric utilities, transportation & other things. The sulphur can be removed for industrial purposes. • If the sulphur is not removed, sulphur combines with hydrogen to form sour gas (H2S) or sulphur dioxide (SO2) Sour gas is very dangerous and sulphur dioxide can form acid deposition

  36. B1.8 Combustion reactions that create nitrous oxides (NOx) • Combustion of fuels at high temperatures (+65C) causes nitrogen in the air to combine with oxygen

  37. Sources & Location of SO2 & NOx producing industries

  38. B1.8 Formation of acid rain oxides during combustion. • CO2 reacts with water to form normal rain with a pH of 5.4. (See next slide for reactions) • SOx & NOx react with water to from acid rain with a pH less than 5.4 (See next slide for reactions)

  39. B1.8 Oxide reactions with water to form acids. • Carbon dioxide + water  carbonic acid • Sulphur dioxide + water  sulphurous acid • Sulphur trioxide + water  sulphuric acid • Nitrogen dioxide + water  nitric acid & nitrous acid Very weak acid Very strong acid Very strong acid

  40. B1.9 What is the effect of acid deposition on the environment?

  41. B1.9 Abiotic effects of acid deposition • Leaching (releasing as ions) of vital nutrients and toxic metals(Al3+, Hg+, Pb2+) into water Biomagnification: The concentration of the ions increases as it moves up the food chain.

  42. B1.9 Abiotic effects of acid deposition • Corrodes buildings and structures made of limestone (carbonate ion), iron or steel.

  43. B1.9 Biotic effects-acid rain Potato scabs • Damage to vegetation – decrease root growth, less absorption of nutrients (Al blocks roots), reduced decomposing soil bacteria, nutrient leaching (yellowing), etc..

  44. B1.9 Biotic effects - acid deposition • Acidification of water systems = death of aquatic organisms; decreased biodiversity (numbers & types of organisms)

  45. B1.9 Why is Alberta not as affected by acid deposition as Eastern Canada? • Jet stream travels from west to east (westerly winds) • Alberta soil has limestone (calcium carbonate – CaCO3) in the soil. The carbonate ion makes the water alkaline (pH > 7) and neutralizes acid deposition (buffered) • Less industry & lower population

  46. Lesson 1.4 Quantifying Acid Deposition

  47. B1.4 Buffer Definition • Buffer is a weak acid and its conjugate base that maintains a constant pH when mixed with a strong acid or base. • The two most common buffers are • carbonic acid/hydrogen carbonate • hydrogen carbonate/carbonate • Strong acids are not buffers.

  48. B1.7 Limestone buffer in soil • Limestone is calcium carbonate (CaCO3) • CaCO3 --> Ca2+ + CO32- • Hydronium ions (acid rain) are absorbed by carbonate ions and weak hydrogen carbonate and water is formed. (see reaction below) • limestone is a natural buffer because it prevents changes in pH by absorbing the acid (hydronium ion)

  49. B1.5 Buffering in the blood • The blood pH is kept at 7.4 with a buffer – carbonic acid and hydrogen carbonate. • Acid – Base reaction with carbonic acid: H2CO3 + HOH  H3O+ + HCO3- Carbonic acid + water  hydronium + hydrogen carbonate • Buffer actions: • Base enters the blood; carbonic acid is converted into hydrogen carbonate and the base is removed • Acid enters the blood; hydrogen carbonate is converted into carbonic acid and the acid is removed

  50. B1.5 Buffer in your stomach • Hydrogen carbonate ions in the walls of your stomach absorb the hydronium ions to form weak carbonic acid. The hydrogen carbonate ions act as a buffer to prevent the walls of your stomach from being eaten by the strong hydrochloric acid.

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