1. Unit B Chemical Reactions

2. Copyright © 2010 Pearson Canada Inc. B - 1 Acids and Bases An acid is a substance that produces hydrogen ions when dissolved in water A base is a substance that produces hydroxide ions when dissolved in water

3. Copyright © 2010 Pearson Canada Inc. B - 2 Acids/Bases and Human Digestion PartsSecretionAcid/base mouthsalivabasic stomachMucusHCl liverBileBase pancreasSodium bicarbonate Base

4. Copyright © 2010 Pearson Canada Inc. B - 3 Organs in Human Digestive System

5. Copyright © 2010 Pearson Canada Inc. B - 4 Identifying Acids and Bases The more hydrogen ions H+, the more acidic; and the lower the pH. The more the hydroxide ions OH-, the more basic; and the higher the pOH The abbreviation “pH” stands for “power of hydrogen”. The pH scale is a number scale that indicates how acidic or basic a solution is

6. Copyright © 2010 Pearson Canada Inc. B - 5 pH Scale

7. Copyright © 2010 Pearson Canada Inc. B - 6 Examples, 1. lemon juice contains citric acid and ascorbic acid (vitamin C). It has a pH of 2-3, and so it is moderately acidic. 2. The more basic a substance is, the higher the pH. e.g. Sodium hydrogen carbonate (baking soda)

8. Copyright © 2010 Pearson Canada Inc. B - 7 Aid to Remember Acids and Bases

9. Copyright © 2010 Pearson Canada Inc. B - 8 Calculating pH values One unit of change on the pH scale is a 10 times change in how acidic or basic a solution is. For example, the hydrochloric acid in your stomach has a pH of 1. This is 10 times more acidic than lemon juice (pH 2). Difference between pH 2 and pH 5 is a 1000 times stronger i.e. 5-2 = 3 =10 3 1000 times more acidic

10. Copyright © 2010 Pearson Canada Inc. B - 9 Acid-Base Indicators Indicators are used to test if a solution is an acid or a base They are substances that change colour in the presence of an acid or a base. e.g. litmus papers and universal indicator Red litmus paper turns blue when it is dipped into a basic solution. Blue litmus paper turns red when it is dipped in an acidic solution.

11. Copyright © 2010 Pearson Canada Inc. B - 10 A pH meter can precisely measure the pH of an acidic or basic solution

12. Copyright © 2010 Pearson Canada Inc. B - 11 Universal indicator is a mixture of chemicals that changes colour through a wide range of pH values Other types of indicators Natural Indicators Red cabbage juice; tea; Rose petals Commercial Indicators Phenolphthalein; Bromothymol blue Congo red; Sudan IV Litmus paper; Universal indicator paper stripes Testing litmus paper

13. Copyright © 2010 Pearson Canada Inc. B - 12 Properties of Acids and Bases See text book Pg 198

14. Copyright © 2010 Pearson Canada Inc. B - 13 Identifying and Naming Acids The chemical formula of acids start with H+ The formula of some acids end with COOH- (mainly weak acids)

15. Copyright © 2010 Pearson Canada Inc. B - 14 Naming Acids That Contain Hydrogen and a Non-Metallic Element Classical names IUPAC Names HCl (aq) hydrochloric aqueous hydrogen acid chloride HF (aq) hydrofluoric acid aqueous hydrogen fluoride Name These: HBr (aq) HI (aq) H2S (aq)

16. Copyright © 2010 Pearson Canada Inc. B - 15 Naming Acids That Contain Polyatomic Ions with Oxygen Atom e.g. Nitrate,NO 3 - ; sulphate,SO 4 2- ;phosphate,PO 4 3- ; chlorate, ClO 3 -

17. Copyright © 2010 Pearson Canada Inc. B - 16 Identifying and Naming Bases Name starts with a metallic ion (or ammonium ion) and ends with hydroxide the chemical formula ends with OH - (called a hydroxyl group) For example NaOH (s), KOH (s), NH 4 OH (aq) Sodium hydroxide (NaOH) is commonly found in drain cleaners and oven cleaners

18. Copyright © 2010 Pearson Canada Inc. B - 17 Naming Bases StepExamples KOH (aq) NH 4 OH (aq) 1. Write the name of the positively charged metallic ion potassiumAmmonium 2. Add the word “hydroxide.” potassium hydroxide Ammonium hydroxide

19. Copyright © 2010 Pearson Canada Inc. B - 18 Chemical & Common Names, Chemical Formula Chemical Names Common Names NaOH (aq) Sodium Hydroxide caustic soda NH4OH (aq) ammonium hydroxide ammonia solution Ca(OH) 2 (s) calcium hydroxide slaked or hydrated lime Mg(OH) 2(s) magnesium hydroxide milk of magnesia

20. Copyright © 2010 Pearson Canada Inc. B - 19 5.2: Neutralization Neutralization is a chemical reaction between an acid and a base that produces water (H2O) and a salt. The salts formed may be soluble in water or can be insoluble. If a salt is insoluble, a precipitate will form. A precipitate is a suspension of small, solid particles formed during a chemical reaction.

21. Copyright © 2010 Pearson Canada Inc. B - 20 Neutralization reactions: acid + base → salt + water HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l) H 2 SO 4 (aq) + NaOH (s) → Na 2 SO 4 (aq) + H 2 O (l)

22. Copyright © 2010 Pearson Canada Inc. B - 21 Practice Problems 1. When HBr (aq) reacts with KOH (aq), a neutralization reaction occurs. The products are KBr (aq) and H 2 O (l). What is the balanced chemical equation for this reaction, including states? 2. When H 2 SO 4 (aq) reacts with Mg(OH) 2 (aq), the products are MgSO 4 (aq) and liquid water. Write the balanced chemical equation for this neutralization reaction, including states.

23. Copyright © 2010 Pearson Canada Inc. B - 22 Applications of Neutralization Reactions 1. In pharmaceutical manufacturing, the pH of a solution may be changed from acidic to basic (or vice versa) so that the desired product forms a precipitate. Precipitate can be purified to produce medications. 2. The calcium carbonate enters into a neutralization reaction with some of the acid in the soil water, and the soil pH becomes more basic. 3. Acid reflux and antacids (Bases)

24. Copyright © 2010 Pearson Canada Inc. B - 23 4. Food industries uses neutralization reactions to adjust the pH of products for preservation. 5. Bee stings can also be treated using a neutralization reaction Bee stings contain methanoic acid, treated with solutions that contain ammonia (base)

25. Copyright © 2010 Pearson Canada Inc. B - 24 Neutralization Reactions and Environment Acid precipitation is rain, snow, fog, or dew that has a pH less than 6. Two main causes of acid precipitation are sulphur dioxide (SO 2 ) and nitrogen oxides ( NO, NO 2, N 2 O, N 2 O 3 ) in the atmosphere. Sulphur dioxide is converted to sulphuric acid by the following two chemical reactions:

26. Copyright © 2010 Pearson Canada Inc. B - 25 2SO 2 (g) + O 2 (g) → 2SO 3 (g) SO 3 (g) + H2O (l) → H 2 SO 4 (aq) Nitrogen dioxide gas dissolves in water droplets in the atmosphere to form nitric acid and fall as acid precipitation. Acid precipitation changes the pH of the soil which causes leaching

27. Copyright © 2010 Pearson Canada Inc. B - 26 Neutralizing Acidic Lakes most lakes are naturally protected from the effects of acid precipitation because they are surrounded by limestone (CaCO 3 ). Most Ontario lakes do not contain limestone and have greater risk of acidification, due to nitric acid and sulphuric acid.

28. Copyright © 2010 Pearson Canada Inc. B - 27 One way to raise the pH of heavily acidified lakes is by adding a substance called lime (CaO). When lime mixes with water, the base calcium hydroxide (Ca(OH) 2 ) is formed. Calcium hydroxide can neutralize both the sulphuric acid and the nitric acid