CHE 105/110 Introduction to Chemistry - Exercises and Answers

1.

Explain the difference between the K_eq and the K_sp.

1.

The K_sp is a special type of the K_eq and applies to compounds that are only slightly soluble.

3.

Write the balanced chemical equation that represents the equilibrium between HF(aq) as reactants and H⁺(aq) and F⁻(aq) as products.

3.

$\text{HF(aq)}\rightleftarrows {\text{H}}^{\text{+}}\text{(aq)}+{\text{F}}^{\text{–}}\text{(aq)}$

5.

Assuming that all species are dissolved in solution, write the K_eq expression for the chemical equation in Exercise 3.

5.

$K_{\text{eq}}=\frac{[{\text{H}}^{\text{+}}{\text{][F}}^{\text{–}}\text{]}}{[\text{HF]}}$

7.

Determine the concentrations of all species in the ionization of 0.100 M HClO₂ in H₂O. The K_a for HClO₂ is 1.1 × 10⁻².

7.

[HClO₂] = 0.0719 M; [H⁺] = [ClO₂⁻] = 0.0281 M

9.

Determine the pH of a 1.00 M solution of HNO₂. The K_a for HNO₂ is 5.6 × 10⁻⁴.

9.

1.63

11.

Write the chemical equations and K_a expressions for the stepwise dissociation of H₃PO₄.

11.

${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{(aq)}\rightleftarrows {\text{H}}^{\text{+}}{\text{(aq) + H}}_{\text{2}}{\text{PO}}_{\text{4}}{}^{\text{–}}\text{(aq);}{K}_{\text{a}}=\frac{{\text{[H}}^{\text{+}}{\text{][H}}_{\text{2}}{\text{PO}}_{\text{4}}{}^{\text{–}}\text{]}}{[{\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{]}}$

${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}{}^{\text{–}}\text{(aq)}\rightleftarrows {\text{H}}^{\text{+}}{\text{(aq) + HPO}}_{\text{4}}{}^{\text{2–}}\text{(aq);}{K}_{\text{a}}=\frac{{\text{[H}}^{\text{+}}{\text{][HPO}}_{\text{4}}{}^{\text{2–}}\text{]}}{[{\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}{}^{\text{–}}\text{]}}$

${\text{HPO}}_{\text{4}}{}^{\text{2–}}\text{(aq)}\rightleftarrows {\text{H}}^{\text{+}}{\text{(aq) + PO}}_{\text{4}}{}^{\text{3–}}\text{(aq);}{K}_{\text{a}}=\frac{{\text{[H}}^{\text{+}}{\text{][PO}}_{\text{4}}{}^{\text{3–}}\text{]}}{[{\text{HPO}}_{\text{4}}{}^{\text{2–}}\text{]}}$

13.

If the K_a for HNO₂ is 5.6 × 10⁻⁴, what is the K_b for NO₂⁻(aq)?

13.

1.8 × 10⁻¹¹

15.

What is [OH⁻] in a solution whose [H⁺] is 3.23 × 10⁻⁶ M?

15.

3.10 × 10⁻⁹ M

17.

What is [H⁺] in a solution whose [OH⁻] is 2.09 × 10⁻² M?

17.

4.78 × 10⁻¹³ M

19.

Write the balanced chemical equation and the K_sp expression for the slight solubility of Mg(OH)₂(s).

19.

${\text{MgOH}}_{\text{2}}\text{(s)}\rightleftarrows {\text{Mg}}^{\text{2+}}{\text{(aq) + 2OH}}^{\text{–}}\text{(aq);}$ K_sp = [Mg²⁺][OH⁻]²

21.

What are [Sr²⁺] and [SO₄²⁻] in a saturated solution of SrSO₄(s)? The K_sp of SrSO₄(s) is 3.8 × 10⁻⁴.

21.

[Sr²⁺] = [SO₄²⁻] = 1.9 × 10⁻² M

23.

What are [Ca²⁺] and [OH⁻] in a saturated solution of Ca(OH)₂(s)? The K_sp of Ca(OH)₂(s) is 5.0 × 10⁻⁶.

23.

[Ca²⁺] = 0.011 M; [OH⁻] = 0.022 M