Chemistry 101 ANSWER KEY 1 REVIEW QUESTIONS Chapter 4 1 ...

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)

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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 

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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

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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)

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