Midterm #1 Review

Miscellaneous

100

What are the definitions of Bronsted-Lowry acids and bases?

Acid = proton donor

Base = proton acceptor

200

What does a lower pKa value tell you about an acid's strength?

The acid is stronger

300

What is the Henderson-Hasselbach equation?

pH = pKa + log([A^-]/[HA])

pH = pKa + log(proton acceptor/proton donor)

400

Explain the trend in acid strength by row and by column.

Row: greater the EN, the stronger the acid

Column: the larger the atomic radius, the stronger the acid

500

Explain what it means to be a stronger weak acid and a stronger weak base.

Stronger weak acid: more deprotonation (not full dissociation), conjugate base does not want to gain H+, the conjugate base is a poor H+ acceptor

Stronger weak base: more protonation (not full dissociation), conjugate acid does not want to lose H+, the conjugate acid is a poor H+ donor

Aqueous Solutions

100

What is the pH of a 0.040M solution of KOH?

12.6

200

Given a pH of 8.52, calculate the concentration of hydroxide ions.

3.31 x 10^-6

300

What is the pKa of a 0.1M solution with a pH of 2.95?

4.9

400

Calculate the percent protonation of a 0.2M solution of a weak base. Kb is 3.6 x 10^-4.

4.25%

500

Find the pH of a solution made from 1.5g of NaOH dissolved in 1.00L of H₂O.

12.57

Salt Solutions

100

Will NaCl have a pH above, below, or equal to 7?

Equal to 7

200

Explain the relevance of Ka and Kb values for determining whether the salt is acidic or basic.

Ka > Kb for acidic

Ka < Kb for basic

Ka = Kb for neutral

the conjugate base from the weak acid is able to do the reverse reaction, same goes for the conjugate acid of a weak base.

300

What type of solution is formed from a strong base and weak acid.

Basic solution

400

Calculate the pH of a 0.35M solution of NaCH₃COO. Ka is 1.8 x 10^-5.

9.15

500

Calculate the pH of a 0.500 M solution of KCN.  Ka for HCN is 5.8 x 10^-10.

11.46

Buffers

100

What are two components that are required to make a buffer?

Weak acid and its conjugate base

Weak base and its conjugate acid

200

Briefly explain how a buffer works.

A buffer prevents changes in pH if acid or base is added. The solution will react with H+ or OH- so the ions do not significantly effect the pH.

300

If a strong base is added to a buffer with NaCH₃COO and CH₃COOH, what ion will it react with? And what will it form?

OH^- ions will react with the acetic acid (CH₃COOH) to form water and acetate ion (CH₃COO^-).

400

Which of the following combinations is NOT a buffer solution?

NH₃ and (NH₄)₂SO4

HBr and KBr

NH₃ and NH₄Br

CH₃COOH and NaCH₃COO

HCN and NaCN

HBr and KBr

500

What is the pH of a buffer solution containing 0.75M of HC₂H₃O₂ and 0.50M NaC₂H₃O₂?

4.57

Titrations

100

For a strong acid and strong base titration, what is the pH at the equivalence point?

7

200

When does the pKa = pH at the mid-equivalence point?

For strong acid/weak base or strong base/weak acid titrations.

300

50mL of a 0.070M HCl solution is titrated with a 0.050M NaOH solution. What is the initial pH before any base is added?

1.15

400

50mL of a 0.070M HCl solution is titrated with a 0.050M NaOH solution. What is the pH before equivalence after 5mL of NaOH is added?

1.23

500

50mL of a 0.070M HCl solution is titrated with a 0.050M NaOH solution. What is the pH at equivalence? What is the pH after 80mL of NaOH is added?

7 @ equivalence

11.58