ANSWERS 1. (a) What compound precipitates when solutions of

ANSWERS

1. (a) What compound precipitates when solutions of Fe

2

(SO

4

)

3

and LiOH are mixed? (b) Write a

balanced equation for the reaction. (c) Will a precipitate form when solutionsof Ba(NO

3

)

2

and

KOH are mixed?

Answers: (a) Fe(OH)

3

; (b) Fe

2

(SO

4

)

3

(aq) + 6 LiOH(aq) → 2 Fe(OH)

3

(s) + 3 Li2SO

4

(aq);

(c) no (both possible products are water soluble)

2. Write the net ionic equation for the precipitation reaction that occurs when solutions of calcium

chloride and sodium carbonate are mixed.

CaCl

2

(aq) + Na

2

CO

3

(aq) → CaCO

3

(s) + 2 NaCl(aq)

Ca

2+

(aq) + 2 Cl

–

(aq) + 2 Na

+

(aq) + CO

3

2–

(aq) → CaCO

3

(s) + 2 Na

+

(aq) + 2 Cl

–

(aq)

Cl

-

and Na

+

are spectator ions. Canceling them gives the following net ionic equation:

Ca

2+

(aq) + CO

3

2–

(aq) → CaCO

3

(s)

3. Write the net ionic equation for the precipitation reaction that occurs when aqueous solutions of

silver nitrate and potassium phosphate are mixed.

Answers: 3 Ag

+

(aq) + PO

4

3–

(aq) → Ag

3

PO

4

(s)

4. (a) Write a balanced molecular equation for the reaction between aqueous solutions of acetic acid

(CH

3

COOH) and barium hydroxide, Ba(OH)

2

. (b) Write the net ionic equation for this reaction.

5. (a) Write a balanced molecular equation for the reaction of carbonic acid (H

2

CO

3

) and potassium

hydroxide (KOH). (b) Write the net ionic equation for this reaction.

Answers: (a) H

2

CO

3

(aq) + 2 KOH(aq) → 2 H

2

O(l) + K

2

CO

3

(aq);

(b) H

2

CO

3

(aq) + 2 OH

–

(aq) → 2 H

2

O(l) + CO

3

2–

(aq). (H

2

CO

3

is a weak acid and therefore a weak

electrolyte, whereas KOH, a strong base, and K

2

CO

3

, an ionic compound, are strong

electrolytes.)

6. Determine the oxidation number of sulfur in each of the following: (a) H

2

S, (b) S

8

,(c) SCl

2

, (d) Na

2

SO

3

,

(e) SO

4

2–

.

(a) S has an oxidation number of –2.

(b) Because this is an elemental form of sulfur, the oxidation number of S is 0 (rule 1).

(c) the oxidation number of S must be +2.

(d) the oxidation number of S in this compound is +4.

(e). the oxidation number of S in this ion is +6.

7. What is the oxidation state of the boldfaced element in each of the following: (a) P

2

O

5

, (b) NaH, (c)

Cr

2

O

7

2–

, (d) SnBr

4

, (e) BaO

2

?

Answers: (a) +5, (b) –1, (c) +6, (d) +4, (e) –1

8. Write the balanced molecular and net ionic equations for the reaction of aluminum with hydrobromic

acid.

2 Al(s) + 6 HBr(aq) → 2 AlBr

3

(aq) + 3 H

2

(g)

Both HBr and AlBr3 are soluble strong electrolytes. Thus, the complete ionic equation is

2 Al(s) + 6 H

+

(aq) + 6 Br

–

(aq) → 2 Al

3+

(aq) + 6 Br

–

(aq) + 3 H

2

(g)

Because Br

–

is a spectator ion, the net ionic equation is

2 Al(s) + 6 H

+

(aq) → 2 Al

3+

(aq) + 3 H

2

(g)

9. (a) Write the balanced molecular and net ionic equations for the reaction between magnesium and

cobalt(II) sulfate. (b) What is oxidized and what is reduced in the reaction?Answers: (a) Mg(s) +

CoSO

4

(aq) → MgSO

4

(aq) + Co(s); Mg(s) + Co

2+

(aq) → Mg

2+

(aq) + Co(s) (b) Mg is oxidized and

Co

2+

is reduced.

10. Which of the following metals will be oxidized by Pb(NO

3

)

2

: Zn, Cu, Fe?

Answer: Zn and Fe

11. Calculate the molarity of a solution made by dissolving 23.4 g of sodium sulfate (Na

2

SO

4

) in enough

water to form 125 mL of solution.

12. Calculate the molarity of a solution made by dissolving 5.00 g of glucose (C

6

H

12

O

6

) in sufficient water

to form exactly 100 mL of solution.

Answer: 0.278 M

13. What are the molar concentrations of each of the ions present in a 0.025 M aqueous solution of

calcium nitrate?

14. What is the molar concentration of K

+

ions in a 0.015 M solution of potassium carbonate?

Answer: 0.030 M K

+

15. How many grams of Na

2

SO

4

are required to make 0.350 L of 0.500 M Na

2

SO

4

?

16. (a) How many grams of Na

2

SO

4

are there in 15 mL of 0.50 M Na

2

SO

4

? (b) How many milliliters of 0.50

M Na

2

SO

4

solution are needed to provide 0.038 mol of this salt?

Answers: (a) 1.1 g, (b) 76 mL

17. How many milliliters of 3.0 M H

2

SO

4

are needed to make 450 mL of 0.10 M H

2

SO

4

?

18. (a) What volume of 2.50 M lead(II) nitrate solution contains 0.0500 mol of Pb

2+

?

(b) How many milliliters of 5.0 M K

2

Cr

2

O

7

solution must be diluted to prepare 250 mL of 0.10 M

solution?

(c) If 10.0 mL of a 10.0 M stock solution of NaOH is diluted to 250 mL, what is the concentration of the

resulting stock solution?

Answers: (a) 0.0200 L = 20.0 mL, (b) 5.0 mL, (c) 0.40 M