Chemistry 101 ANSWER KEY REVIEW QUESTIONS
Chapter 4
1. Identify each of the following substances as a non-electrolyte (NE), weak
electrolyte (WE), or strong electrolyte (SE):
a)
HF
WE
b)
C2H5OH
NE
c)
LiOH
SE
d)
HClO3
SE
e)
Cu(NO3)2
f)
H3PO4
WE
SE
2. Complete each equation shown below:
a)
H 2 O
AlCl3 (s) ¾¾¾
® Al3+ (aq) + 3 Cl – (aq)
b)
H 2 O
Na3PO4 (s) ¾¾¾
® 3 Na+ (aq) + PO43– (aq)
c)
H 2 O
(NH4)2CO3 (s) ¾¾¾
® 2 NH4+ (aq) + CO32– (aq)
3. Complete the molecular equations shown below, and write balanced net
ionic equations for each:
a)
Pb(NO3)2 (aq) + Na2SO4 (aq) ® PbSO4 (s) + 2 NaNO3 (aq)
Pb2+ (aq) + SO42– (aq) ® PbSO4 (s)
b)
Cr(OH)3 (aq) + 3 HNO3 (aq) ® Cr(NO3)3 (aq) +
OH–
+
H+
®
H2O (l)
1 3 H2O (l)
4. For each reaction shown below, determine if a reaction occurs. If so, write a
balanced net ionic equation. If not, write “No Rxn”.
a)
Ca(OH)2 (aq) + 2 HCN (aq) ® Ca(CN)2 (aq) + 2 H2O (l)
OH– (aq) + HCN (aq) ® CN– (aq) + H2O
b)
2 AgNO3 (aq) + Na2CO3 (aq) ® Ag2CO3 (s) + 2 NaNO3 (aq)
2 Ag+ (aq) + CO32– ® Ag2CO3 (s)
c)
NaCl (aq) + (NH4)2SO4 (aq) ® No Rxn
d)
Na3PO4 (aq) + 3 HBr (aq) ®
H3PO4 (aq) + 3 NaBr (aq)
PO43– (aq) + 3 H+ ® H3PO4 (aq)
5. Write balanced net ionic equations for each reaction described below:
a) Solid sodium hydroxide pellets are dropped in solution of sulfuric acid.
2 NaOH (s) + H2SO4 (aq) ® Na2SO4 (aq) + 2 H2O (l)
NaOH (s) + H+ (aq) ® Na+ (aq) + H2O (l)
b) Aqueous solutions of ammonium carbonate and calcium chloride are
mixed together.
(NH4)2CO3 (aq) + CaCl2 (aq) ® CaCO3 (s) + 2 NH4Cl (aq)
CO32– + Ca2+ ® CaCO3 (s)
2 6. How many grams of solute are present in 50.0 mL of 1.33 M CuSO4 solution? 50.0 mL x 1.33 mol CuSO 4 159.55 g x = 10.6 g CuSO 4 1000 mL 1 mol 7. How many mL of 1.50 M Na3PO4 solution contains 5.00 g of solute? 1 mol 1000 mL 5.00 g x x = 20.3 mL 164.0 g 1.50 mol 8. What volume of 1.50 M solution of sucrose solution is required to prepare 425 mL
of 0.100 M solution? V2 = M 1 V 1 (0.100 M )(425 mL) = = 28.3 mL M 2 1.50 M 9. Glacial acetic acid has a density of 1.049 g/mL at 25°C. What is the molarity of a
solution of acetic acid prepared by dissolving 10.00 mL of glacial acetic acid at 25°C
in enough water to make 100.0 mL of solution? 10.00 mL x 1.049 g 1 mol 1 x x
=1.747 M 1 mL 60.04 g 0.1000 L 10. How many mL of 2.15 M KOH are required to titrate 25.0 mL of 0.300 M HC2H3O2?
HC2H3O2 + KOH ® KC2H3O2 + H2O 25.0 mL HC2 H 3O 2 x 0.300 mol 1 mol KOH 1000 mL x x = 3.49 mL KOH
1000 mL 1 mol HC2 H 3O 2 2.15 mol 3 11. Determine the concentration of a Ba(OH)2 solution, if 15.0 mL of the base are
required to titrate 25.0 mL of 0.525 M HNO3 to an end point.
2 HNO3 + Ba(OH)2 ® Ba(NO3)2 + 2 H2O 25.0 mL HNO 3 x 0.525 mol 1 mol Ba(OH) 2 1 x x
= 0.438 M 1000 mL 2 mol HNO 3 0.0150 L 12. A 28.7 mL sample of 1.02 M HCl is required to neutralize the NH3 present in a
5.00 mL sample of window cleaner solution. What is the molarity of NH3 in this
solution?
HCl + NH3 ® NH4Cl 28.7 mL HCl x 1.02 mol 1 mol NH 3 1 x x
= 5.85 M 1000 mL 1 mol HCl 5.00x10 ­3 L 13. The acetylsalicylic content of aspirin can be determined by titration of the acid with
base as shown below:
HC9H7O4
+
acetylsalicylic acid
NaOH ®
NaC9H7O4
+
H2O
23.0 mL of 0.0770 M NaOH solution was used to neutralize the acid in a 500-mg
aspirin tablet. What is the percent of acetylsalicylic acid in the aspirin tablet?
HC9H7O4 + NaOH ® NaC9H7O4 + H2O 23.0 mL NaOH x 0.0770 mol 1 mol HC9 H 7 O 4 180.1 g 103 mg x x x = 319 mg HC9 H 7 O 4 1000 mL 1 mol NaOH 1 mol 1 g % Acid = 319 mg x100 = 63.8% 500 mg
4 14. In the compounds below, assign oxidation numbers to the underlined element:
a)
H3PO2
P : +1
d) H2CO
C:
0
b)
Na2C2O4
C : +3
e) ClF4–
Cl :
+3
c)
MnSO4
S:
g) AlH3
H:
–1
+6
15. Identify which substance is oxidized and which substance is reduced in each
of the following redox reactions. 0 a)
0 +3 –1 2 Al + 3 Cl2 ® 2 AlCl3
oxidized
–2 b)
0 Al
reduced
Cl S
reduced
O reduced
N
–2 +4 2 NiS + 3 O2 ® 2 NiO + 2 SO2
oxidized
–2 +5 0 +2 c) 3 H2S + 2 HNO3 ® 3 S + 2 NO + 4 H2O
Oxidized
S
16. For each reaction shown below, write oxidation and reduction half-reactions.
a)
Fe (s) + Cu2+ (aq) ® Cu (s) + Fe2+ (aq)
Oxidation half-reaction:
Fe (s) ® Fe2+ (aq) + 2 e–
Reduction half-reaction:
Cu2+ (aq) + 2 e– ® Cu (s)
b) Mg (s) + 2 HCl (aq) ® MgCl2 (aq) + H2 (g)
Oxidation half-reaction:
Mg (s) ® Mg2+ (aq) + 2 e–
Reduction half-reaction:
2 H+ (aq) + 2 e– ® H2 (g)
5