S25 Exam 4 Review

Acid/base strength

100

You are given two acids:

• Acid A has a Ka = 1.3 × 10⁻⁵

• Acid B has a Ka = 6.2 × 10⁻⁴

Which is the stronger acid

Acid B

200

Which factor(s) contribute most to the strength of a binary acid (e.g., H-X)? What is the relationship?

A. Electronegativity of X
B. Bond strength between H and X
C. Atomic radius of X
D. Molar mass of X

B. Bond strength between H and X

C. Atomic radius of X

decreasing bond strength --> increasing acid strength

NOTE: Electronegativity is only for analyzing the strength of oxyacids, not binary acids.

300

Given the following list of acids, which one would produce the conjugate base that forms the most basic aqueous solution at equal concentrations? 

H₂O, NH₄⁺, HCN

H₂O

The weakest acid yields the strongest conjugate base

pH, Ka, etc calculations

100

You have a 0.0010 M HCl solution.
What is the pH and pOH of the solution?

pH = 3.00

pOH = 11.00

200

A 0.20 M solution of acetic acid (CH₃COOH) has a pH of 2.72.
Find the Ka of acetic acid.

Ka = 1.8x10^-5

300

A 0.050 M solution of ammonia (NH₃) has a Ka=5.5x10^-10.
Find the pH of the solution.

pH = 10.98

Buffers and Salts

100

Which of the following could be used for a buffer?
(A) HF/ KBr
(B) HNO₂ / NaNO₂
(C) NH₄Cl / NH₃
(D) C₆H₅OH / NaC₆H₅O

(B) HNO₂ / NaNO₂
(C) NH₄Cl / NH₃
(D) C₆H₅OH / NaC₆H₅O

A weak acid/base conjugate pair is what you want.

200

Consider the titration of 50.0 mL of 0.120 M HNO₂ with 0.200 M KOH. What is the pH of the solution after 10.0 mL of KOH is added. The Ka of HNO₂ is 4.468x10^-4.

pH = 3.049

300

Determine whether the following 0.100M solutions of NaClO, CaCl₂, KNO₂, and C5H5NH⁺Br⁻ will be basic, acidic, or neutral.

NaClO: basic

CaCl₂: neutral

KNO₂: basic

C5H5NH⁺Br⁻: acidic

Titrations

100

Consider the titration of 50.0 mL of 0.120 M HNO2 with 0.200 M KOH.
Draw the titration curve for this titration.

Should look like the titration curve of a weak acid and strong base.

200

A 0.100M solution of NaOH is titrated with 20.0mL of 0.125M CH₃COOH (Ka=1.8x10^-5). Calculate the pH after adding 30.0mL of NaOH.

pH = 12.00

300

A 25.0 mL of a 0.10 M HCl solution is titrated with a 0.10 M NaOH solution. Calculate the pH after 5.00mL of NaOH solution have been added.

 

pH = 1.17

Solubility equilibria and past exam review

100

Which of the following solutions will have the lowest freezing point?
(A) 0.010 m RbI 

(B) 0.015 m SrBr₂

(C) 0.035 m CH₃OH

(B) 0.015 m SrBr₂

200

The solubility product constant (Ksp) for barium sulfate (BaSO₄) is 1.10 × 10⁻¹⁰ at 25 °C.

What is the molar solubility of BaSO₄ in pure water at 25 °C?

1.05x10^-5M

300

Draw the Lewis structure of HCN and its conjugate.

see slides for answers