Chem 121-2010 Problem Set #2

1. How many sulphur atoms are there in 3.8 mol of sulphur?

2. What is the amount, in moles, of each of the following?

a) 11.8 g Ar; b) 3.55 g Zn; c) 26.1 g Ta; d) 0.211 g Li

3. How many atoms are in each of the following?

a) 5.18 g P; b) 2.26 g Hg; c) 1.87 g Bi; d) 0.082 g Sr

4. Determine the number of moles of hydrogen atoms in each of the following:

a) 0.0885 mol C₄H₁₀; b) 1.3 mol CH₄; c) 202. g C₆H₁₂; d) 214 g C₈H₁₈

5. Calculate the mass, in grams, of a single platinum atom.

6. Calculate the mass percent composition of carbon in each of the following carbon compounds:

a) CH₄; b) C₂H₆; c) C₂H₂; d) C₂H₅Cl

7. Samples of several compounds are decomposed and the masses of their constituent elements are shown below. Calculate the empirical formula for each compound.

a) 1.651 g Ag, 0.1224 g O                              b) 0.672 g Co, 0.569 g As, 0.486 g O

8. Calculate the empirical formula for each of the following stimulants based on their elemental mass percent composition:

a) nicotine: 74.03% C, 8.70% H, 17.27% N

b) caffeine: 49.48% C, 5.19% H, 28.85% N, 16.48% O

9. The empirical formula and molar mass of several compounds are listed below. Find the molecular formula of each compound.

a) C₆H₇N, 186.24 g/mol; b) C₂HCl, 181.44 g/mol; c) C₅H₁₀NS₂, 296.54 g/mol

10. The foul odour of rancid butter is due largely to butyric acid, a compound containing carbon, hydrogen, and oxygen. Combustion analysis of a 4.30 g sample of butyric acid produced 8.59 g CO₂ and 3.52 g H₂O. Find the empirical formula for butyric acid.

11. Combustion analysis of a hydrocarbon, containing only C and H, produced 33.01 g CO₂ and 13.51 g H₂O. Calculate the empirical formula of the hydrocarbon.

12. Balance each of the following chemical equations:

a) CO₂(g)  +  CaSiO₃(s)  +  H₂O(l)  ®  SiO₂(s)  +  Ca(HCO₃)₂(aq)

b) Co(NO₃)₃(aq)  +  (NH₄)₂S(aq)  ®  Co₂S₃(s)  +  NH₄NO₃(aq)

c) C₆H₆(l)  +  O₂(g)  ®  H₂O(l)  +  CO₂(g)

13. Write a balanced chemical equation for the fermentation of sucrose(C₁₂H₂₂O₁₁) by yeast in which the sugar reacts with water to form aqueous ethyl alcohol(C₂H₅OH) and carbon dioxide gas.

Answer Set for Chem 121-2010 Problem Set #2:

1. 2.3×10²⁴ S atoms

2.a) 0.295 mol Ar; b) 0.0543 mol Zn; c) 0.144 mol Ta; d) 0.0304 mol Li

3.a) 1.01×10²³ atoms; a) 6.78×10²¹ atoms; a) 5.39×10²¹ atoms; a) 5.6×10²⁰ atoms

4.a) 0.885 mol H; b) 5.2 mol H; c) 28.8 mol H; d) 33.7 mol H

5. 3.240×10^-22 g

6.a) 74.87% C; b) 79.88% C; c) 92.24%C; d) 37.23% C

7.a) Ag₂O; b) Co₃As₂O₈

8.a) C₅H₇N; b) C₄H₅N₂O

9.a) C₁₂H₁₄N₂; b) C₆H₃Cl₃; c) C₁₀H₂₀N₂S₄

10. C₂H₄O

11. CH₂

12.a) 2CO₂(g)  +  CaSiO₃(s)  +  H₂O(l)  ®  SiO₂(s)  +  Ca(HCO₃)₂(aq)

b) 2Co(NO₃)₃(aq)  +  3(NH₄)₂S(aq)  ®  Co₂S₃(s)  +  6NH₄NO₃(aq)

c) 2C₆H₆(l)  +  15O₂(g)  ®  6H₂O(l)  +  12CO₂(g)

13. C₁₂H₂₂O₁₁(s)  + H₂O(l)  ®  4C₂H₅OH(aq)  +  4CO₂(g)