1. Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases
Living By Chemistry
Unit 4: TOXINS
Stoichiometry, Solution Chemistry, and Acids and Bases

2. Lesson 19: pHooey!
[H+] and pH

3. ChemCatalyst
Pure water has an H+ concentration of 1.0 x 10–7 M and an OH– of 1.0 X 10–7 M.
What does this mean?

4. Key Question
How is pH related to the acid or base concentration of a solution?

5. You will be able to:
explain the mathematical relationship between the H+ and OH– concentrations in a solution
define pH and explain the relationship between H+ concentration and pH
determine the H+ concentration of a solution given the [OH–], and vice versa

6. Prepare for the Lab Work in groups of four.
Wear safety goggles at all times.
Acids and bases are corrosive. Do not get any on skin or near eyes.
In case of a spill, rinse with large amounts of water.

7. Discussion Notes
The pH scale is a logarithmic scale that describes the concentration of H+ ions in solution.
pH is related to [H+] by the formula
pH = -log [H+]

8. Discussion Notes (cont.)
More acidic
H+ concentration
OH– concentration pH
1.0 X 100 M
1.0 X 10–14 M
1.0 X 10–1 M
1.0 X 10–13 M 1
1.0 X 10–2 M
1.0 X 10–12 M 2
1.0 X 10–3 M
1.0 X 10–11 M 3
1.0 X 10–4 M
1.0 X 10–10 M 4
1.0 X 10–5 M
1.0 X 10–9 M 5
1.0 X 10–6 M
1.0 X 10–8 M 6
1.0 X 10–7 M 7 8 9
1.0 X 10–0 M 14
neutral
More basic

9. Discussion Notes (cont.)
In any solution, the product of the hydrogen ion, H+, concentration and hydroxide ion, OH–, concentration is a constant.
Water dissociates into H+ and OH– ions.

10. Wrap Up
How is pH related to the acid or base concentration of a solution?
The pH scale is a logarithmic scale that describes the concentration of hydrogen ions, H+, in solution: pH = -log [H+].
The H+ concentration is related to the OH– concentration: [H+][OH–] =10–14. So, as [H+] increases, [OH–] decreases, and vice-versa.
The pH of water is 7. In water the H+ concentration is equal to the OH– concentration. Thus, water is neutral.

11. Check-in
If you know the pH of a solution, what else do you know?

12. Lesson 21: Neutral Territory
Neutralization Reactions

13. ChemCatalyst
Excess stomach acid, HCl, can cause extreme discomfort and pain. Milk of magnesia, Mg(OH)2, is often taken to reduce stomach acid.
What products do you think are produced when Mg(OH)2 and HCl are mixed?
What products do you think are produced when HNO3 and HCl are mixed?

14. Key Question
What happens when acids and bases are mixed?

15. You will be able to:
write a chemical equation for an acid-base neutralization reaction
describe how the pH changes when acids and bases are mixed

16. Prepare for the Lab Work in pairs. Wear safety goggles at all times.
Acids and bases are corrosive. Do not get any on skin or near eyes.
In case of a spill, rinse with large amounts of water.

17. Discussion Notes
A neutralization reaction between a strong acid and a strong base in aqueous solution produces an ionic compound (salt) and water.
A neutralization reaction can be described as a double exchange reaction in which the two compounds exchange cations.

18. Wrap Up What happens when acids and bases are mixed?
A neutralization reaction between a strong acid and a strong base produces an ionic salt and water.
When strong acids and bases are mixed, the pH of the product approaches 7 at 25 °C.

19. Check-in
Sulfuric acid, H2SO4(aq), reacts with magnesium hydroxide, Mg(OH)2(aq). Write a balanced equation for the reaction that occurs.

20. Lesson 22: Drip Drop
Titration

21. ChemCatalyst
A student mixes 100 mL of 0.10 M HCl with different volumes of 0.10 M NaOH.
1: 100 mL of 0.10 M HCl + 50 mL of 0.10 M NaOH
2: 100 mL of 0.10 M HCl mL of 0.10 M NaOH
3: 100 mL of 0.10 M HCl mL of 0.10 M NaOH
a. Which solution is the least toxic?
b. Are the final solutions acid, basic, or neutral?

22. Key Question
How can a neutralization reaction help you figure out acid or base concentration?

23. You will be able to: explain and complete a titration procedure
use titration data to determine the molarity of a solution whose concentration is unknown

24. Prepare for the Lab Work in pairs. Wear safety goggles at all times.
Acids and bases are corrosive. Do not get any on skin or near eyes.
In case of a spill, rinse with large amounts of water.

25. Discussion Notes HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
The chemical equation for the neutralization reaction shows the ratio in which the substances combine.
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

26. Discussion Notes (cont.)
A titration is a procedure in which a neutralization reaction is monitored with an indicator allowing you to calculate the unknown concentration of an acid or base.
When the equivalence point is reached in a titration between a strong acid and a strong base, the number of moles of H+ ions equals the number of moles of OH– ions.

27. Wrap Up
How can a neutralization reaction help you figure out acid or base concentration?
A titration is a procedure that allows you to calculate the unknown concentration of an acid or a base using a neutralization reaction.
During a titration, an indicator is used to signal when the equivalence point has been reached.

28. Check-in
A beaker has 50 drops of HCl, along with a drop of phenolphthalein indicator.
After 100 drops of 0.10 M NaOH are added, the color changes from clear to bright pink. What is the concentration of the original HCl solution?