Chemistry Exam 3

Titrations

100

Consider the titration of 75 mL of 0.35 M HCl with 0.25 M NaOH. What is the pH at the equivalence point?

pH = 7

Strong acid strong base

200

Consider the titration of 105 mL of 0.45 M weak acid (Ka = 5.0 x 10-5) with 0.55 M strong base. What is the pH after the addition of 80 mL of strong base? 

pH = 3.17

300

Consider the titration of 100 mL of 0.60 M weak acid (Ka = 3.6 x 10-5) with 0.70 M strong base. What is the pH after the addition of 50 mL of strong base? 

pH 4.3

400

Consider the titration of 235 mL of 0.45 M weak acid (Ka = 4.8 x 10-5) with 0.15 M strong base. What is the pH after the addition of 120 mL of strong base? 

pH 3.63

500

onsider the titration of 125 mL of 0.55 M weak acid (Ka = 4.9 x 10-5) with 0.35 M strong base. What is the pH after the addition of 75 mL of strong base?

pH=4.1

Titration Curves

100

What is point A? 

Equivalence point

200

What is the pink Region?

Buffer region

300

What is being titrated?

a base

400

What should the X axis be?

Volume of acid added

500

What should the Y axis be?

pH

ICE tables

100

Consider the titration of 50.0 mL of 2.0 M HNO₂ (Ka = 4.0x10^-4) with 1.0 M KOH. Create an Ice table but do not solve it. 

[HNO2]             [NO₂]                 [H₃O+]

2.0                      0                          0
-x                      +x                        +x
2.0 – x               +x                        +x

200

Create an ICE table but do not solve for a solution that contains 0.139 M acetic acid 

HC₂H₃O₂(aq) = H⁺(aq) + C₂H₃O₂^-(aq)

HC₂H₃O₂(aq) = H⁺(aq) + C₂H₃O₂^-(aq)

.139                  0               0

-x                   +x             +x

.139-x              x                x

300

Find the pH of a 0.275 M hypochlorous (HClO) acid solution. Ka = 3.0 x 10-8.

HClO = H⁺ + ClO^-

.275  0  0

-x +x +x

.275-x +x +x

3x10^-8=x²/(.275-x)   assume x is small

x = 9.08x10^-5

pH = - log (9.08 x 10-5) = 4.042

400

The acid dissociation constant (Ka) for benzoic acid is 6.3 x 10^-5. Find the pH of a 0.35 M solution of benzoic acid. 

HC₇H₃O₂(aq) = H⁺ + C₇H₃O₂-(aq)

.35  0  0

-x  +x  +x

.35-x +x +x

6.3 x 10^-5= x²/(.35-x)     assume x is small

x = 4.7 x 10^-3

pH = - log (4.7 x 10^-3) = 2.33

500

A 10.0-mL sample of 0.50 M NH3 is titrated with 0.50 M HCl. What is the pH of the solution after 10.0 mL of HCl has been added? This is the equivalence point! Ka of NH4+ = 5.6 x 10^–10

pH = 4.9

Acids and Bases

100

Describe the acidity/basicity of a solution made when dissolving KCl in water. (Basic, Acidic, Neutral)

Neutral, KOH and Hal strong base and strong acid.

200

HOBr

HOBrO3

HOBrO2

Which is the strongest acid?

HOBrO3

Most O atoms when molecules are the same but different # of O atoms

300

Describe the acidity/basicity of a solution made when dissolving NH4Br in water. (Acidic, Basic, Neutral)

Acidic NH4- weak base Br- Strong acid

400

Which of the following is a Lewis acid, but not a Bronsted-Lowry acid?

A) CH3NH2 B) CH3COOH C) HNO3 D) H2O E) BCl3

 

BCl₃

500

Nitrous acid has a Ka of 4.0 x 10–4. It would be most effective for preparation of a buffer with a pH of 1, 3, 5, 7, or 9

3. pka=-log(Ka)  pH=pka 

= 3.4 round to 3

True or False

100

The pOH for a solution with [H3O+] = 2.5 x 10-5 M is 9.4.

True 

200

HNO3 and CH3COOH could function as a buffer solution.

False. needs to be weak acid/base and strong acid/base depending on the first compound. Strong acid and weak acid. 

300

The pH of a 0.30 M solution of benzoic acid is 5.22. Ka of benzoic acid = 6.6x10-5

False the pH = 3.99

400

H₂SO₄ and H₄SO₄ are conjugate acids/bases.

False

500

According to Brønsted and Lowry the conjugate acid of CH3OH is CH₃OH₂⁺

True! the base accepts a proton!