2-6 Acids/Base Chemistry

1. 2-6 Acids/Base Chemistry

2. Just as you can classify compounds as ionic or covalent, you can classify some compounds as being either acids or a bases.

3. Acids • Taste sour • Release H+ ions in aqueous solution HCl H+ + Cl- • Produce a solution with a pHless than 7 • Can be corrosive Common Examples: Ascorbic acid = vitamin C, found in juices & citrus Stomach acids used to break down food

4. Bases • Feel slippery • Taste bitter • Release OH- ions in aqueous solution NaOH Na+ + OH- • Produce a solution with a pH greater than 7 • Can be corrosive Common Examples: Soap, oven cleaner, baking soda

5. pH Scale • This is a scale (0 – 14) used to indicate how acidic or basic something is • pH < 7 = acidic • pH > 7 = basic • pH = 7 = neutral

6. pH Scale • Substances that are closer to 0 are more acidic • Substances that are closer to 14 are more basic • Sometime you will hear bases referred to as alkaline

7. pH Scale • The units on the pH are a little strange • Each 1 unit increase actually represents an change in 10x the acidity or basicity Examples: pH = 4 is 10x more acidic than pH = 5 pH = 9 is 10x more basic than pH = 8 Regular rain = pH 6, acid rain = pH 4. How much more acidic is the acid rain?

8. pH Scale • Lemons are ____ times more acidic than grapes • Tomatoes are ____ times more acidic than grapes • Oven cleaner is _____ times more basic than soap.

9. pH Indicators • Since acids and bases can be dangerous, chemists use special chemicals called indicators to determine whether a solution is acidic or basic • pH indicators change colour. • They are one colour in acids and a completely different colour in bases.

10. pH Indicators Litmus paper: • Red in acid, blue in base • Can tell you if a solution is acidic or basic, but not HOW acidic or basic it is.

11. pH Indicators Universal Indicator: • Made up of a number of different indicator solutions that turn different colours for each step in the pH scale • Can give you a general idea of the pH of a solution.

12. pH Indicators pH meters or pH computer probes: • These devices measure electrical properties of solutions to very accurately determine pH

13. pH Indicators

14. Complete the Reading Check Questions on page 225

15. Acids • If you know a compound’s chemical formula, you may be able to identify whether it is an acid. They will have either: • The “H” written at the beginning of the formula. Examples: • HCl (aq) = hydrochloric acid • HNO3(aq) = nitric acid • The “H” written at the end of the formula IF the acid contains the element carbon. Example: • CH3COOH = acetic acid • Acids often behave like acids only when dissolved in water. • Therefore, acids are written with symbol (aq) = aqueous

16. Acids • Naming acids Complete the Reading Check on page 227

17. Bases • If you know a compound’s chemical formula, you may be able to identify it as a base. • Bases often behave like bases only when dissolved in water. • Therefore, bases are often written with the symbol (aq) = aqueous = water. • The chemical formula of a base usually ends with hydroxide (OH). • Bases can be gentle or very caustic. • Examples of common bases: • NaOH(aq) • Mg(OH)2(aq) • Ca(OH)2(aq) • NH4OH(aq)

18. Complete the Reading Check Questions on page 228.

19. Production of Ions • Acids and bases can conduct electricity because they release ions in solution. • Acids release hydrogen ions, H+. • Bases release hydroxide ions OH–. • The pH of a solution refers to the concentration of ions it has.

20. Production of Ions • Square brackets are used to signify concentration, [H+], [OH–] • High [H+] = low pH, very acidic • High [OH–] = high pH, very basic • A solution cannot have BOTH high [H+] and [OH–]; they cancel each other out and form water. This process is called neutralization. H+ + OH– H2O

21. Properties of Acids & Bases

22. Complete Checking Concepts page 233 #1-15

23. Acid-Base Neutralizations

24. A neutralization reaction happens when an acid and a base react to form a salt and water. Acid + Base  Salt + Water HCl + NaOH  NaCl + H2O • A salt is made up of a positive ion from a base and a negative ion from an acid.

25. Neutralization Reaction ACID + BASE  SALT + WATER • Neutralization reactions can happen for any acid and base combination Example: 3H2SO4 + 2Al(OH)3  Al2(SO4)3 + 6H2O Acid + Base  Salt + Water

26. Practice: • HCl + KOH  • H3PO4 + NaOH  • H2CO3 + Mg(OH)2  • CH3COOH + LiOH 

27. Complete the Practice Problems on page 236

28. Metal Oxides • Metals react with oxygen to form oxides • A compound made up of one or more oxygen with one or more other elements • Metal oxides consist of a metal chemically combined with oxygen • Metal oxides react with water to form bases. • Na2O(s) + H2O(l)  2NaOH(aq)

29. Non-Metal Oxides • Non-metal oxides consist of a non-metal chemically combined with oxygen • Non-metal oxides react with water to form acids. • SO2(g) + H2O(l)  H2SO3(aq) • Non-metal oxides are formed from the burning of fossil fuels. • Acid added to water in the atmosphere = acid precipitation.

30. Practice: • CO2 + H2O  • CaO + H2O  • NO3 + H2O 

31. Complete the reading check questions on page 238

32. Acids and Metals • The most reactive metals, at the bottom of groups 1 and 2 on the periodic table, react vigorously with water and acids. • All other metals are less reactive than those in groups 1 and 2. • When metals do react with acids, H2 gas is usually released. 2HCl(aq) + Mg(s)  MgCl2(s) + H2(g)

33. Practice: • HCl + Zn  • HBr + Al  • H2SO4 + Ca 

34. Complete the Practice Problems on Page 238

35. Acids and Carbonates • Much of the carbon dioxide on Earth is trapped in rocks as limestone, dolomite, and calcite that contain carbonate (CO3-2) ions. • Carbonates neutralize acids, protecting locations with natural carbonate supplies from acid precipitation. • H2SO4(aq) + CaCO3(s)  CaSO4(s) + H2O(l) + CO2(g) sulphuric calcium calcium water carbon acid carbonate sulphate dioxide

36. Complete the Check Your Understanding questions on page 243 #1-12