Dr. White
Chem 1A
Fall 2013
1
Exam 4 Practice Problems
1. a. Define "oxidation".
b. Identify the oxidizing and reducing agents in the following (unbalanced) equation.
HNO3(aq) + C2H6O(aq) + K2Cr2O7(aq) → KNO3(aq) + C2H4O(aq) + H2O(l) + Cr(NO3)3(aq)
2. For each of the following species, write down, next to the formula, the oxidation number of the indicated
atom.
a. P in H2PO2
b. S in Na2S2O3
c. C in CH2O
3. In both of the following reactions, a precipitate is formed. Complete and balance the equations, showing the
phases of the products.
a. AgNO3(aq) + CaCl2(aq) →
b. NaOH(aq) + Fe(NO3)3(aq) →
4. For the reactions in #3, 100.0mL of a 0.250 M solution of each reactant is mixed together. Calculate the
concentration of all the ions and the mass of precipitate once the reaction is complete. Assume the volumes are
additive.
5. A 1.00-L sample of a pure gas weighs 0.785 g and is at 0.965 atm and 29.2°C.
a. What is the molar mass of the gas?
b. If the volume and temperature are kept constant while 0.400 g of the same gas are added to that already in
the container, what will the new pressure be?
6. In the fermentation process, yeast converts glucose to ethanol and carbon dioxide. What volume of carbon
dioxide, measured at 745 torr and 25.0°C, can be produced by the fermentation of 10.0 g of glucose?
C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(g)
7. Balance the following reactions:
2a. Bi(OH)3(s) + Sn(OH)3 (aq) → Sn(OH)6 (aq) + Bi(s) (basic solution)
b. I (aq) + NO3 (aq) → NO(g) + I2(s) (acidic solution)
8. Aluminum oxide (used as an adsorbent or a catalyst for organic reactions) forms when aluminum reacts with
oxygen. A mixture of 82.49 g of aluminum (
= 26.98 g/mol) and 117.65 g of oxygen (
= 32.00 g/mol) is
allowed to react. What mass of aluminum oxide (
= 101.96 g/mol) can be formed?
9. Magnesium (used in the manufacture of light alloys) reacts with iron(III) chloride. A mixture of 41.0 g of
magnesium ( = 24.31 g/mol) and 175 g of iron(III) chloride (
= 162.2 g/mol) is allowed to react. Identify the
limiting reactant and determine the mass of the excess reactant present in the vessel when the reaction is
complete.
10. Kaolinite, a clay mineral with the formula Al4Si4O5(OH)4, is used as a filler in slick-paper for magazines and
as a raw material for ceramics. Calculate the mass percent of each element in kaolinite.
11. Analysis of a white solid produced in a reaction between chlorine and phosphorus showed that it contained
77.44% chlorine and 22.56% phosphorus. What is its empirical formula?
12. A 11.3 g sample of a compound containing only carbon, hydrogen and oxygen was burned completely in air
to produce 16.6 g of CO2 and 6.80 g of H2O. What is the empirical formula of this compound?
13. An insecticide has the weight percents C = 55.6%, H = 4.38%, Cl = 30.8% and O = 9.26%. The approximate
molar mass is 345 g/mol. What is the molecular formula?
14. Crystalline potassium hydrogen phthalate KHC8H4O4 is used to standardize basic solutions. If 1.548 g of
this salt is titrated with a solution of Ca(OH)2, the end point is reached when 42.37 mL of the solution has been
added. What is the molarity of the Ca(OH)2 solution?
Dr. White
Chem 1A
Fall 2013
2
15. What volume, in mL, of 0.150 M NaOH is required to precipitate all of the nickel(II) from 75.0 mL of 0.225 M
Ni(NO3)2?
16. A gas occupies 250. mL at 700. torr and 300. K. What volume (mL) will the gas occupy at 350. torr and
450.K?
17. A 65.0 L gas cylinder at 5.1 atm and 20°C contains only nitrogen gas. What is the mass (in grams) of the
nitrogen in the tank?
18. What volume (in L) is occupied by 3.50 g of chlorine gas at 45°C and 745 mm Hg?
19. What is the density (g/L) of carbon dioxide at 30.3°C and 744 mm Hg?
20. The density of a gaseous element at 310.°C and 775 mm Hg is 2.64 g/L. What is the molar mass of the
element?
21. A bulb with a volume of 225 mL contains 0.580 g of an unknown gaseous compound. The pressure is
measured as 145.60 kPa at a temperature of 25°C. What is the molar mass of the compound?
22. Calcium reacts with water to produce 2 products (one is a gas). At STP, what volume (L) of hydrogen would
be produced by the reaction of 1.2 grams of calcium?
23. Write the chemical formulas for the predicted products (if no reaction occurs, write NR). Then, balance the
reaction and write the net ionic equation. Finally, list which type of reaction it is. Please include phase labels for
your predicted products.
a. Na2CO3(aq) + HNO3(aq) →
b. CoSO4(aq) + Na2S (aq) →
c. Copper (II) sulfate (aq) + zinc (s) →
d. Na (s) +
H2O (l) →
e. NaNO3 (aq) + Ag (s)
f.
Acetic Acid + aqueous calcium hydroxide →
g. NaBr (aq) + KCl (aq)
Δ
h. NO2 (g) ⎯
⎯
→
i. Mg (s) + nitrous acid →
2+
24. An ore of iron is converted into a solution of Fe and is titrated with KMnO4 solution. If a 0.500 g sample of
ore requires 28.72 mL of 0.0193 M KMnO4, what is the percent of iron in the iron ore? (Start with the balanced
€
redox reaction.
The reaction occurs in an acidic solution)
Exam 4 Practice Problem Key
1.
a. Oxidation: loss of electrons or increase in oxidation number.
b. Oxidizing agent is K2Cr2O7(aq); reducing agent is C2H6O(aq).
2.
a. +1
b. +2
c. 0
3.
a. 2AgNO3(aq) + CaCl2(aq) → 2AgCl(s) + Ca(NO3)2(aq)
b. 3NaOH(aq) + Fe(NO3)3(aq) → Fe(OH)3(s) + 3NaNO3(aq)
+
2+
4.
a. 0.00 M Ag ; 0.125 M Cl ; 0.125 M NO3 ; 0.125 M Ca ; 3.58 g AgCl
3+
+
b. 0.00 M OH ; 0.0833 M Fe ; 0.125 M Na ; 0.375 M NO3 ; 0.740 g Fe(OH)3
5.
a. 20.2 g/mol
b. 1.46 atm
6. 2.77 L
+
2+
7. a. Bi(OH)3 + 3 H + 3e → Bi + 3H2O
Sn(OH)3 + 3H2O → Sn(OH)6 + 3H + 2e
+
2+
2Bi(OH)3 + 6 H + 6e → 2Bi + 6H2O
3Sn(OH)3 + 9H2O → 3Sn(OH)6 + 9H + 6e
+
2+
2Bi(OH)3 + 6 H + 6e + 3Sn(OH)3 + 9H2O →2Bi + 6H2O + 3Sn(OH)6 + 9H + 6e
Dr. White
Chem 1A
-
Fall 2013
2-
+
2Bi(OH)3 + 3Sn(OH)3 + 9H2O → 2Bi + 6H2O + 3Sn(OH)6 + 3H
2+
2Bi(OH)3 + 3Sn(OH)3 + 3H2O → 2Bi + 3Sn(OH)6 + 3H
+ 3 OH
+ 3 OH
22Bi(OH)3 + 3Sn(OH)3 + 3 OH + 3H2O → 2Bi + 3Sn(OH)6 + 3H2O
22Bi(OH)3 + 3 OH + 3Sn(OH)3 → 2Bi + 3Sn(OH)6
b. I (aq) + NO3 (aq) → NO(g) + I2(s) (acidic solution)
+
2I → I2 + 2e
NO3 + 4H + 3e → NO + 2H2O
+
6I → 3I2 + 6e
2NO3 + 8H + 6e → 2NO +4H2O
+
6I + 2NO3 + 8H + 6e → 3I2 + 6e + 2NO +4H2O
+
6I + 2NO3 + 8H → 3I2 + 2NO +4H2O
8. 155.8 g
9. Limiting reactant is FeCl3; 2 g of Mg remain.
10. 20.90% Al 21.76% Si
55.78% O
1.56% O
11. PCl3
12. CH2O
13. C16H15Cl3O2
14. 0.08945 M
15. 225 mL
16. 750. mL
2
17. 3.9 x 10 g
18. 1.31 L
19. 1.73 g/L
20. 124 g/mol
21. 43.8 g/mol
22. 0.67 L
23.
a. Na2CO3(aq) + 2HNO3(aq) → 2NaNO3 (aq) + H2O (l) + CO2 (g)
2+
NIE: CO3 (aq) + 2H (aq) → H2O (l) + CO2 (g)
Type: Acid-Base
b. CoSO4(aq) + Na2S (aq) → CoS (s) + Na2SO4 (aq)
2+
2NIE: Co (aq) + S (aq) → CoS (s)
Type: ppt
c. CoSO4 (aq) + Zn (s) → ZnSO4 (aq) + Co (s)
2+
2+
NIE: Co (aq) + Zn (s) → Zn (aq) + Co (s)
Type: single replacement
d. 2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
+
NIE: 2Na (s) + 2H2O (l) → 2Na (aq) + 2OH (aq) + H2 (g)
e. NR
f. 2HC2H3O2 (aq) + Ca(OH)2 (aq) → Ca(C2H3O2)2 (aq) + H2O (l)
NIE: 2HC2H3O2 (aq) + 2OH (aq) → 2C2H3O2 (aq) + H2O (l)
Type: Acid-Base
g. NR
Δ
h. 2NO2 (g) ⎯
⎯→ N2 (g) + 2O2 (g)
Δ
NIE: 2NO2 (g) ⎯
⎯→ N2 (g) + 2O2 (g)
Type: decomposition
i. Mg (s) + 2 HNO2 (aq) → Mg(NO2)2 (aq) + H2(g)
2+
NIE: Mg (s) + 2 HNO2 (aq) → Mg (aq) + 2 NO2 (aq) + H2(g)
€
Type: Single displacement
€
24. 31.0%
3