Chem 107
Problem set #2
Salah S. Massoud
Part I: Multiple Choices. Please circle the ONE best answer:
1. The number of ions formed when Al(NO3)3 is dissolved in water is:
a) 13
b) 3
c) 2
d) 4
2. What volume of 0.650 M HCl is needed to completely neutralize 12 g of NaOH (40.0 g/mol)?
a) 462 mL
b) 0.462 mL
c) 18.5 mL
d) 11.0 mL
3. Which of the following species is a weak acid in water?
a) HCl
b) NH3
c) HC2H3O2
4. For the reaction: Mg (s) + H2SO4 (aq)
a) Mg2+ and Cl5.
b) Mg2+ and H+
d) HNO3
MgSO4 (aq) + H2 (g), the spectator ion(s) are:
c) SO42- and H+
d) only SO42-
If a student accidentally mixed 400. mL of 0.35 M HCl with 100 mL of 0.65 M HCl.
What would be the final molarity of hydrochloric acid solution?
a) 1.0 M
b) 0.41 M
c) 0.35 M
d) 0.65 M
6. Calculate the molarity of 0.105 g of backing soda (NaHCO3, molar mass = 84 g/mol) in 2.5 mL of
solution.
b) 5.0 x 10-4 M
a) 0.042 M
c) 0.05 M
7. For the reaction: CaCO3 (s) + 2 HCl (aq)
The net ionic equation is
CaCl2(aq) + CO2 (g) + H2O (l)
a) CO32- + 2 H+
H2O (l) + CO2 (g)
b) CO32- + 2 H+
H2CO3
c) CO32- + H+
d) 42 M
HCO3-
d) CaCO3 (s) + 2 H+
Ca2+ + CO2 (g) + H2O (l)
8. Which of the following is a weak electrolyte:
9.
a) potassium chloride (KCl)
b) hydrobromic acid (HBr)
c) aqueous ammonia (NH3)
d) Nitric acid (HNO3)
For the reaction: 2 Al (s) + 3 H2SO4 (aq)
ion(s) are:
a) Al3+ and SO42-
b) Al3+ and H+
Al2(SO4)3 (aq) + 3 H2 (g), the spectator
c) SO42- and H+
d) only SO42-
10. If 380.0 mL of 0.350 M NaOH is added to 250.0 mL of 0.65 M HNO3, will the mixture be
a) acidic
b) basic
c) neutral
d) amphoteric
1
11. Which of the following equations DO NOT represent an oxidation?
a)
a)
b)
c)
MnO2
SO2
Zn
2 I-
Mn2+
SO3
Zn2+
I2 (l)
12. The oxidation numbers for arsenic in AsO43- and As2O3 are:
a) +5 and +3, respectively
c) +5 and -6, respectively
b) +5 and +6, respectively
d) –3 and 0, respectively.
13. In the reaction: H2S (aq) + 4 Br2 (aq) + H2O (l)
oxidizing agent is
a) H2S
b) Br2
H2SO4 (aq) + 8 HBr (aq), the
c) H2O
d) H2SO4
14. The oxidation numbers of sulfur, S in H2S and S2O42- are:
a) -2 and +3, respectively
b) -2 and +6, respectively
c) +2 and +3, respectively
d) –2 and +8, respectively
15. Calculate the molarity of F- in a 250.0 mL solution containing 18.34 g LiF and 4.32 g NaF?
a) 0.810
b) 0.202
c) 4.77
d) 3.24
Part II: Chemical equations and formulas:
1. Balance the following ionic redox reaction in acidic medium:
Cr2O72- (aq) + SO2 (g)
Cr3+ (aq) + SO42- (aq)
Then indicate:
a) The oxidation step: ----------------------------------------------------b) The reduction step: ------------------------------------------------------c) The oxidizing agent: ------------------------------------------------------d) The reducing agent: -------------------------------------------------------e) The number of electrons that is transferred per mole of the reducing agent: -----------2. Write balanced chemical equations for each of the following. Including physical states as (s, l, g
aq) and be careful about the type of arrow you use as
or
(Use the periodic chart
for charges on each ion. Use reference sheet).
a) Write the equation which represents what happened when Na2CO3 is dissolved in water:
b) Write the equation (if any) of a solution of KNO3 with a solution of Na2CO3.
c) Write the NET IONIC equation for the reaction of Na2CO3 (aq) with CaCl2 (aq)
2
Part III Show all work for full credit. Please express all answers with proper units and correct
number of significant figures.
1. What volume in milliters of 0.1234 M HCl is needed to neutralize 2.00 g Ca(OH)2 (74.1 g/mol)?
2. The density of ethanol, C2H6O, is 0.789 g/mL. Calculate the number of moles of 25.0 mL of
C2H6O?
3. How many grams of HCl are needed to react with 6.25 g of Al according to:
2 Al (s) + 6 HCl(aq)
2 AlCl3 (aq) + 3 H2 (g)
4. Exactly 20.0 g of SiO2 and 7.00 g of C are allowed to react according to the balanced equation:
SiO2 (s) + 3 C (s)
SiC (s) + 2 CO (g)
a. What is the maximum amount of carbon monoxide that can be formed?
b. If you perform the experiment and isolate 4.50 g CO, what is the percent yield?
5. Consider the following reaction:
2 Cr (s) + 3 Br2 (l)
2 CrBr3 (s)
a. How many grams of bromine are required to react completely with 10.00 g of chromium?
b. How many grams of chromium and bromine are required to produce 29.17 g of CrBr3?
6. The density of liquid bromine is 3.10 g/mL. What volume of bromine will be required to react
with 5.87 g of aluminum according to the equation below?
2 Al (s) + 3 Br2 (l)
Al2Br6 (s)
7. A chemist mixes 80.0 g of manganese(IV) oxide with 100.0 g hydrochloric acid under conditions
for the following reaction:
MnO2 (s) + 4 HCl (aq)
2 MnCl2 (s) + Cl2 (g) + 2 H2O (l)
a. What is the maximum number of grams of Cl2 that can be produced?
b. Which reagent will be totally consumed (limiting reactant)?
c. What is the percent yield of the reaction, if 44.7 g of Cl2 is produced?
8.
Peroxyacylnitrate is one of the components of smog. It is a compound of C, H, N, and O. It has
the following percent composition by mass: 19.8% C, 2.59% H, 11.6% N, and 66.0% O.
a. Determine the simplest formula of the compound.
b. What is the molecular formula of the compound if its molar mass is about 121 g.
9. You can dissolve an aluminum soft drink can in an aqueous base such as potassium hydroxide
according to the reaction:
2 Al (s) + 2 KOH (aq) + 6 H2O (l)
2 KAl(OH)4 (aq) + 3 H2 (g)
If you place 12.55 g of Al in a beaker with 250. mL of 1.29 M KOH, will any Al remain after the
reaction has taken place? What mass of KAl(OH)4 is produced?
3
Answers:
Part I-Multiple Choices:
1) d
6) c
11) a
2) a
7) d
12) a
3) c
8) c
13) b
4) d
9) d
14) a
5) b
10) a
15) d
Part-II:
1) Cr2O72- (aq) + 3 SO2 (g) + 2 H+ (aq)
a)
b)
c)
e)
2 Cr3+ (aq) + 3 SO42- (aq) + H2O
The oxidation step: SO2 (g)
SO42- (aq)
2The reduction step: Cr2O7 (aq)
2 Cr3+ (aq)
2The oxidizing agent: : Cr2O7 (aq)
d) The reducing agent is SO2 (g)
The number of electrons that is transferred per mole of the reducing agent: 2
2) a) Na2CO3
2 Na+ (aq) + CO32- (aq)
b) N. R.
c) Ca2+ (aq) + SO42- (aq)
CaSO4 (s)
Part III-Calculations:
1) 437 mL
2) 0.428 mol of C2H6O
3) 25.3 g of HCl
4) a- C is the L.R.; 10.9 g of CO & b- percent yield = 41.4% CO
5) a- 46.10 g Br2 & b- 5.200 g of Cr and 23.97 g of Br2.
6) 16.8 mL of Br2
7) a-HCl is the limiting reactant, 0.686 mol Cl2 = 48.6 g Cl2; b- HCl is totally consumed;
c- Percent yield = (44.7g Cl2/48.6g Cl2)x100 = 92.0%
8) a- C2H3NO5 & b- C2H3NO5
9) KOH is the L.R., 43.3 g of KAl(OH)4, Al is in excess and some will remain un-reacted.
4
5