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The midterm test for 1998 is on Oct. 29 between 7:00 and 8:30 pm. If you have a class or another examination scheduled during this time, please click here, or check the Chem120 Info.

## Sample MidTerm Test

### Warning!

• The Mid Term Tests are set by your instructor, and his style and problems may be very different from these sample problems.
• ### Mid Term Test Example Problems

The answers are given at the end of the Instruction, and there are a few more practice questions in the Dialogue.

1. A compound consists of 68.1 % C, 13.7 % H and 18.2 % O. What is its empirical formula?
A C68H14O18
B C5H12O
C C4H10O2
D C3H8O
E C2H6O

2. Antimony(III) oxide is produced by burning antimony metal in air,
4 Sb(s) + 3 O2(g) -> 2 Sb2O3(s)
How much antimony is needed to prepare 425 kg of Sb2O3 if the yield
is 94.0 %?
A 292 kg
B 259 kg
C 710 kg
D 355 kg
E 378 kg

3. What is the molar concentration of K2CrO4 in a solution which contains 22.0 % K2CrO4 by weight, and has a density of 1.192 g/mL?
A 1.13 M
B 1.35 M
C 0.0950 M
D 1.19 M
E 0.220 M

4. Which statement is not correct?
1. Oxygen gas (M=32.0) will effuse through a tiny pinhole 1.4142 times as fast as sulfur dioxide (M=64.0) at the same temperature and pressure, in the same apparatus.
2. At a given temperature, H2 gas molecules have a higher average speed than N2 gas molecules (M=28.0).
3. The density of H2 (g) is greater than the density of N2(g) at the same temperature and pressure.
4. The boiling point of a liquid is the temperature at which the liquid's equilibrium vapour pressure equals the surrounding atmospheric pressure.
5. Given 2 NO(g) + O2 (g) -> 2 NO2 (g), the reaction of 1.0 L of NO (g) with 1.0 L of O2 (g) would give a gas mixture with final volume of 1.5 L, after the limiting reagent has been consumed -- all measurements at the same temperature and pressure.

5. A mixture of N2 (g) and O2 (g) occupies a volume of 335 mL at 538 torr and 24 °C. If the partial pressure of O2 (g) is 246 torr, what amount of N2(g) is present?
A 0.00445 mol N2 (g)
B 0.00973 mol N2 (g)
C 0.00528 mol N2 (g)
D 0.0654 mol N2 (g)
E 0.120 mol N2 (g)

6. Using standard heat of formation data from the data sheet, determine the standard heat of combustion for 1.00 mole of C2H5OH(l) with excess O2.
(Data sheet is not given here, but you may consult a text
for data).
A -402
B -1235
C -1367
D -1922
E -2199

7. Given the enthalpies for the reactions (all reactants and products are gases) HF => H + F,         DH = 568 kJ
H2 => 2 H,            DH = 463 kJ
H2 + F2 => 2 HF,   DH = -542 kJ
What is the DH for the reaction F2 => 2 F A 262 kJ
B 131 kJ
C -131 kJ
D -262 kJ
E Non of the above

8. A gas at 25 °C is contained in a closed cylinder with a moveable piston. Its volume is 5.00 L and its pressure is the same as the atmospheric pressure of 96.3 kPa. The gas is heated to 50 °C, by adding 101 J of heat, while it expands against the atmospheric pressure to a new volume of 5.50 L. What is change in inter energy E for the gas?
A 101 J
B 149 J
C 53 J
D -101 J
E 202 J

9. Which of the following statements about the Hall-Heroux process for the electrolytic production of aluminum is or are correct?
1. The mixture of cryolite and alumina has a much lower melting point than either pure cryolite or pure alumina.
2. During electrolysis the carbon anode is consumed and CO2 is formed.
3. The molten aluminum that forms is drawn off from the bottom of
electrolysis cell.
A a
B b
C a and b
D b and c
E a, b and c

10. A 2.00 g mixture of CaCl2 and NaCl is dissolved in water. Then, AgNO3 was added, and the resulting dry AgCl weighs a g. If the 2.0 g mixture contains x g CaCl2, and y g NaCl, which one of the following statements is correct?
A x + y = a
B x = 2 + y
C x / (molar mass of CaCl2) + y / (molar mass of NaCl) = a
D 2 x / (molar mass of CaCl2) = moles of Cl- from CaCl2
E a / (molar mass of AgCl) = number of mole of NaCl

Two more versions are available: Version 1 has 7 questions, and Version 2 has 10 questions.

## Confidence Building Questions

A container holding a mixture of gases A and B where the mole fraction of A is xA = 0.65 had a tiny hole leaking into a vacuum, and it takes 6 times as long for a given small quantity of gas B to effuse from the container as it does the same amount of gas A. If the molar mass of gas A is 72.0 g mol-1, what is the molar mass of B in g mol-1?
This is not an easy question!

Eactly 1.00 mol of a sample of pure NOBr (g) is sealed into a rigid 10.0-L vessel and heated to 350 K, at which temperature it undergoes a partial decomposition via the reaction NOBr (g) = NO (g) + (1/2) Br2 (g) If the final total pressure in the vessel is found to be 380.0 kPa, what fraction of the original NOBr molecules have dissociated?

A mixture is prepared by placing 30.0 grames of ethyne, C2H2, and 3.00 grames of H2 in a 10.0 L vessel at 40 degree C. When a catalyst is added to the mixture, ethane is formed as result of the reaction C2H2 (g) + 2 H2 (g) = 1 C2H6 What is the limiting reagent?

A mixture is prepared by placing 30.0 grames of ethyne, C2H2, and 3.00 grames of H2 in a 10.0 L vessel at 40 degree C. When a catalyst is added to the mixture, ethane is formed as result of the reaction C2H2 (g) + 2 H2 (g) = 1 C2H6 What is the pressure inside the vessel when the limiting reagent has been consumed?

Which one of the following is not a basic SI unit?

Choose the incorrect statement regarding gases:

Which statements is false?