Chemistry Chapter 19

1
Chemistry Chapter 19

• Practice with acids and bases

2
Calculate the pH

• A solution is found to contain 3.65 x 10-3
  mol/liter HCl, a strong acid.
• What is the pH of the solution?
• What is the hydroxide ion concentration in the
  solution?

3
Calculate the pH

• A solution is found to contain 3.65 x 10-3
  mol/liter HCl, a strong acid.
• What is the pH of the solution?
• pH -logH
• - log(3.65 x 10-3) 2.44
• Because the solution has an ion concentration of
  greater than 1 x 10-7, it is an acidic solution.
• Also because the pH is less than 7, we know it is
  acidic.

4
Calculate the pH

• A solution is found to contain 3.65 x 10-3
  mol/liter HCl, a strong acid.
• What is the hydroxide ion concentration in the
  solution?
• OH- ion concentration can be found by using Kw.
• Kw HOH-
• 1 x 10-14 (3.65 x 10-3)(x)
• 2.74 x 10-12

5
Working backwards

• A solution has a pH of 9.3. Using a mathematical
  approach, show that the solution is acidic or
  basic.

6
Solution

• Acids have an H concentration of 1 x 10-7 or
  greater. We will therefore calculate the
  concentration using pH -logH.
• 9.3 -log(x) or antilog -9.3 x
• x 3.17 x 10-10
• The solution is basic because the H ion
  concentration is less than 1 x 10-7

7
More practice

• What is the pH of a solution that contains 5.44 x
  10 5 M NaOH?

8
Solution

• What is the pH of a solution that contains 5.44 x
  10 5 M NaOH?
• Two ways to do this
• solve for the H, or calculate pOH and then use
  pKw to get pH

9
Solution

• What is the pH of a solution that contains 5.44 x
  10 5 M NaOH?
• 1 x 10-14 HOH-
• 1 x 10-14/5.44 x 10-5 H 1.84 x 10-10
• pH -log(1.84 x 10-10) 9.7 - basic

10
Other solution

• What is the pH of a solution that contains 5.44 x
  10 5 M NaOH?
• pOH -logOH-
• -log(5.44 x 10-5) 4.26
• pKw pH pOH or 14 4.26 pH
• pH 9.74 (answers are the same)

11
Polyprotic acids

• Many acids release more than one proton.
• Examples H2SO4, H3PO4, H2C2O4
• When these dissociate, they change the pH
  differently. Strong acids will donate all
  protons from H, weak will not donate even all
  the first ions.

12
Example

• Calculate the pH of a 0.002 M H2SO4 solution.

13
Solution

• Calculate the pH of a 0.002 M H2SO4 solution.
• H 2(0.002) 0r 0.004 M H ions
• pH -log(0.004) 2.40

14
Problem

• What is the H ion concentration if the OH- ion
  concentration is 1 x 10-4 M? Kw for water is 1.0
  x 10-14
• Is this solution an acid or a base?

15
Problem

• Show the neutralization reaction of acetic acid,
  a weak acid, and sodium hydroxide, a strong base.

16
Problem

• If I were to put sodium acetate salt into water,
  would the solution be acidic, basic, or neutral?
  Why?

17
Problem

• What acids and bases will produce ammonium
  chloride?
• When placed in water, would the solution be
  acidic, basic, or neutral? Why?

18
Problem

• When placed in water would the solution of sodium
  bromide be acidic, basic or neutral?
• What color would it turn a strip of litmus paper?

19
Questions

• What consitutes a strong acid?
• What constitutes a weak acid?
• What is a conjugate acid? How does it differ
  from a conjugate base?
• What is the difference between Bronsted lowry
  acids and Arrhenius acids?