June 23, 2009
Student’s Name:
Answers
Test 2A
Chemistry 110
Formula used
Answers
1.
E
2.
C
3.
E
4.
C
5.
E
6.
C
7.
E
8.
E
9.
D
10. E
11. D
12. B
13. B
14. B
15. C
16. C
17. D
18. D
19. A
20. B
21. E
22. C
23. A
24. C
25. E
26. E
27. B
Formula used
Short Answers
1. (5 pts) A compound consisting of C, H and O only, has a molar mass of 331.5 g/mol. Combustion of 0.1000 g of this
compound produced 0.2921 g of CO2 and 0.0951 g of H2O. What are the molecular and empirical formulas of this
compound?
CxHyOz +
0.1000 g
O2

CO2
+
0.2921 g
H 2O
0.0951 g
Mass C = 0.2921 x 12.01 = 0.0797 g
44.01 g
Mass H = 0.0951 x 2.02 = 0.01066 g
18.02 g
Mass O = 0.100g – ( 0.0951 + 0.01066) = 0.00964 g
Moles of C = 0.0797g = 6.636 x10-3 mol
12.01g
Moles of H = 0.01066g = 1.055 x10-2 mol
1.01g
Moles of O = 0.00964g = 6.025 x10-4 mol
16.00
Ratios are (C : H : O) = (11 : 17.5 : 1) which is (22 : 35 : 2)
The empirical and Molecular formulas are C22H35O2
2. (6 pts) Consider the balanced equation:
Al2S3(s) + 6H2O (l)  2Al(OH)3(s) + 3H2S(g)
If 15.0g of aluminum sulfide and 10.0g of water are allowed to react as above, and assuming a complete reaction
a) by calculation, find out which is the limiting reagent.
b) calculate the maximum mass of H2S which can be formed from these reagents.
c) calculate the mass of excess reagent remaining after the reaction is complete.
15.0 g Al2S3 x 1 mol Al2S3 x 3 mol H2S x 34.08 g H2S = 10.2 g H2S
150.14 g
1 mol Al2S3 1 mol H2S
10.0 g H2O x 1 mol H2O x 3 mol H2S x 34.08 g H2S = 9.42 g H2S Limiting reactant
18.02 g
6 mol H2O
mol H2S
a) H2O is the limiting Reactant
b) Mass of H2S formed is 9.42 g
c) Mass of Al2S3 that has reacted: 10.0 g H2O x 1 mol H2O x 1 mol Al2S3 x 150.14 g Al2S3 = 13.89 g Al2S3 reacted
18.02 g
6 mol H2O
1 mol Al2S3
Mass of Al2S3 leftover = 15.0 g – 13.89 g = 1.1 g of Al2S3 leftover.
3. Give formulas for names and names for formulas (8 pts)
Names
Formulas
Formulas
Names
Iron (II) Sulfate
FeSO4
Hg2I2
Mercury (I) iodide
Cobalt (III) oxide
Co2O3
HClO2 (aq)
Chloric Acid
Potassium dichromate
K2Cr2O7
P4O10
Tetraphosphorus decoxide
Lead (IV) sulfide
PbS2
SO3
Sulfur trioxide
Magnesium sulfate heptahydrate
MgSO4.7H2O
NH4NO2
Ammonium nitrite
Titanium (IV) permanganate
Ti(MnO4)4
AgCN
Silver cyanide
Gold (III) Iodide
AuI3
H2O2
Hydrogen peroxide
Hydrogen sulfide
H2S
H2SO3 (aq)
Sulfurous acid