CHM 1045 Spring, 2013
Test 2
Name (print)___________________
Show your work for complete (and partial) credit. Report your answers to the correct
number of significant figures, and use units where appropriate. NA=6.022x1023
1. Balance the following chemical equation.
___NH4NO3(s) → ___N2(g) + ___O2(g) + ___H2O(g)
2. What is the percent by mass of nitrogen in (NH 4)2S?
3. a) What is the mass of one (average) carbon atom in amu?
b) What is the mass of one (average) carbon atom in grams?
The following information applies to the next three problems.
Compound: MgCl2
Mg(NO3)2 AgCl
AgNO3
f.w.(g/mol): 95.211
148.435
143.321
169.87
MgCl2(aq) + 2AgNO3(aq) → 2AgCl(s) + Mg(NO3)2(aq)
4. How much does 0.055mol of magnesium chloride weigh?
5. What mass of MgCl2 is required to form 1.223g of AgCl?
6. An impure sample of MgCl2(s) weighing 1.250g was dissolved in 100.mL of water.
Excess AgNO3(aq) was added to completely react the MgCl2(aq). The AgCl
precipitate was filtered, dried, and weighed. It weighed 2.718g. What was the purity
of the original MgCl2 sample?
7. What is the theoretical yield, in grams, of the product if 25.0g of each reactant are
allowed to react by the reaction 2Mg(s) + O2(g)  2MgO(s)
8. What is the empirical formula for a compound that is 3.250% hydrogen, 19.36%
carbon, and 77.39% oxygen (by mass)?
9. A sample of a hydrocarbon (contains only C and H) was combusted for elemental
analysis. The products of the combustion were carbon dioxide and water in a ratio
(CO2:H2O by moles) of 2:3. What is the empirical formula for the hydrocarbon?
10. a) In the reaction, Mg(s) + Cl2(g)  MgCl2(s), what is the oxidizing agent?
b) In the net ionic reaction Cu(s) + 2Ag+(aq)  Cu+2(aq) + 2Ag(s),
____ is oxidized to ____ and ____ is reduced to ____.
11. Write a balanced chemical equation (net ionic or molecular, balanced, phases) for the
reaction that occurs when solutions of calcium hydroxide and sulfuric acid (H 2SO4)
are mixed.
12. Provide the oxidation number of each of the underlined species.
a) MnO4 b) H2SO4
c) ZnCl2
d) NH4+
e) Cl2
13. Indicate whether the following reactions are precipitation, acid/base, or
oxidation/reduction reactions. Check the appropriate boxes.
Reaction
precip.
2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(l)
2AgNO3(aq) + Cu(s)  Ag(s) + Cu(NO3)2(aq)
H2SO4(aq) + Zn(s)  ZnSO4(aq) + H2(g)
H2SO4(aq) + Na2CO3(aq)  CO2(g) + H2O(l) + Na2SO4(aq)
H2SO4(aq) + BaCl2(aq)  BaSO4(s) + 2HCl(aq)
a/b
ox/red
14. Write the net ionic equation for the following reaction.
2 HCl(aq) + Mg(s) → H2(g) + MgCl2(aq)
15. Aqueous solutions of barium nitrate and sodium sulfate were mixed. A sulfate
compound precipitated. Write a net ionic equation for the reaction that occurred.
16. Predict the products of the following reactions, given that on the activity series, H 2 is
above Cu. If no reaction will occur, write "nr".
a) H2(g) + Cu(s) →
b) H2(g) + CuCl2(aq) →
c) 2H+(aq) + Cu(s) →
d) 2H+(aq) + CuCl2(aq) →
The following information applies to the next two problems.
Compound: MgCl2
Mg(NO3)2 AgCl
AgNO3
f.w.(g/mol): 95.211
148.435
143.321
169.87
MgCl2(aq) + 2AgNO3(aq) → 2AgCl(s) + Mg(NO3)2(aq)
17. What volume of 0.250M MgCl2(aq) contains 5.11g of MgCl2?
18. What volume of 0.250M MgCl2 is required to form 0.222g of AgCl?
19. In the titration of a 25.00mL sample of H2SO4 of unknown concentration, 35.55mL of
0.222M NaOH was required to reach the endpoint. What was the concentration of the
sulfuric acid sample?
20. Pb(NO3)2(aq) + 2NaI(aq) → PbI2(s) + 2NaNO3(aq)
Compound:
Pb(NO3)2
NaI
PbI2
NaNO3
f.w. (g/mol)
331.2
149.9
461.1
84.995
In an experiment similar to Experiment 4 (Limiting Reactant), a student reacted 1.000g
of a mixture of lead nitrate and sodium iodide. The reaction produced 0.646g of PbI 2.
What mass of the excess reactant, Pb(NO3)2, remained unreacted?