Chem 11 - Exam #2 Sample

Sample Exams are designed to give you an idea of the types of questions you can expect.  Questions may not exactly agree with currently assigned material, so you may need to examine other sample exams.  Answers for Sample Exam #2 are available.

1. Solve the following solution problems:

a. A 20.0-g sample of HF is dissolved in water to give 2.0 x 10² mL of solution. What is the concentration of the solution?

b. How many grams of solute are contained in 141 mL of a 0.175 M silver nitrate solution?

c. If all of the chloride in a 5.000-g sample of an unknown metal chloride is precipitated as AgCl with 70.90 mL of 0.2010 M AgNO₃, what is the percentage of chloride in the sample?

d. Calculate the volume of 5.0 M HF that will react with 7.4 g of calcium hydroxide react completely, according to the reaction 2HF + Ca(OH)₂ ---> CaF + 2H₂O?

e. Sulfamic acid, HSO₃NH₂ (molar mass = 97.1 g/mol), is a strong monoprotic acid that can be used to standardize a strong base:

HSO₃NH₂ (aq) + KOH(aq) ---> KSO₃NH₂ (aq) + H₂O(l)

A 0.179-g sample of HSO₃NH₂ required 19.4 mL of an aqueous solution of KOH for complete reaction. What is the molarity of the KOH solution?

2. Answer each of the following ideal gas law questions.

a. A gas sample is heated from -20.0^oC to 57.0^oC and the volume is increased from 2.00 L to 4.50 L. If the initial pressure is 0.125 atm, what is the final pressure?

b. It is found that 250. mL of gas at STP has a mass of 1.00 g. What is the molar mass?

c. Calculate the density of nitrogen at STP.

d. If a 2.15-g sample of a gas occupies 750. mL at STP, what is the molar mass of the gas at 125^oC?

e. A mixture of 1.00 g H₂ and 1.00 g He is placed in a 1.00-L container at 27^oC. Calculate the partial pressure of each gas, and the total pressure in the container.

3. Show the correct oxidtion state for nitrogen in each of these compounds.

HNO₃ _____________________________

NO₂ _____________________________

N₂O _____________________________

NH₄Cl _____________________________

NaNO₂ _____________________________

Na₃N _____________________________

4. A 130.-mL sample of gas is collected over water at 22^oC and 753 torr. What is the volume of the dry gas at STP? (The vapor pressure of water at 22^oC = 20. torr.)

5. A vessel with a volume of 10.0 L contains 2.80 g of nitrogen gas, 0.403 g of hydrogen gas, and 79.9 g of argon gas. At 25^oC, what is the total pressure in the vessel? What is the partial pressure of each gas?

6. For the following strong electrolytes, show the ions that each would produce when these salts are dissolved in water.

NaBr ____________________________________

MgCl₂ ____________________________________

Al(NO₃)₃ ____________________________________

(NH₄)₂SO₄ ____________________________________

HI ____________________________________

FeSO₄____________________________________

KMnO₄ ____________________________________

HClO₄ ____________________________________

7. Balance the following oxidation-reduction equation(s). Show the appropriate half reactions when the reaction is performed in solutions of acid or base (indicated).

C₃H₅(NO₃)₃ ---> N₂ + CO₂ + H₂O + O₂ (formula for the explosion of nitroglycerin in dynamite)

I^- + NO₃^- ---> NO + I₂ (acid)

Cr₂O₇^2- + I^- ---> Cr³⁺ + IO₃^- (acid)

Zn + As₂O₃ ---> AsH₃ + Zn²⁺ (acid)

MnO₄^- + Br^- ---> MnO₂ + BrO₃^- (base)

Bi(OH)₃ + SnO₂^2- ---> Bi + SnO₃^2- (base)

8. In a certain experiment, 28.0 mL of 0.250 M H₂SO₄ and 53.0 mL of 0.320 M KOH are mixed. Calculate the amount of water formed in the resulting reaction. What is the concentration of either H⁺ or OH^- ions in excess after the reaction goes to completion?

9. Write the complete balanced equation, the complete ionic equation and the net ionic equation for the reaction between KOH and iron(III) nitrate. Then, assuming you start with3.45 g of KOH, how much solid will you produce in this reaction?

10. You need to prepare exactly 225 mL a 0.1500 M solution of NaOH. You can start with a concentrated 55% NaOH solution (550 g NaOH/1000 mL solution). How much of the original, concentrated solution will you need? How many grams of solute will be present in the final volume of diluted solution that you prepared?

11. Answer each of the following:

___ T ___F Polar molecules have an unequal distribution of charge within the molecule.
___ T ___F An acid is a substance that produces OH^- ions in water.
___ T ___F The filtrate is the solid formed when two solutions are mixed.
___ T ___F A chemical that changes color at the endpoint of a reaction is called a colorimeter.
___ T ___F Oxidation is the gain of electrons.
___ T ___F A reducing agent is an electron donor.
___ T ___F A half-reaction contains only reactants.
___ T ___F When aqueous solutions of sodium sulfide and copper(II) chloride are mixed together, both NaCl and CuS precipitate from solution.
___ T ___F A gas that obeys Boyle's law is a real gas.
___ T ___F At the same temperature lighter molecules have a higher average velocity than heavier molecules.
___ T ___F Effusion and diffusion are the same process.
___ T ___F Real gases deviate from ideal behavior at high temperatures and low pressures.
___ T ___F The two main sources of air pollution are transportation and heavy industry.
___ T ___F A weak electrolyte dissociates to a slight extent in an aqueous solution.
___ T ___F Spectator ions participate directly in reactions

12. Four identical 1.0-L flasks contain the gases He, Cl₂, CH₄, and NH₃, each at 0^oC and 1 atm pressure. Which gas has the highest density? ___________

Argon has a density of 1.78 g/L at STP. Which of the following gases has a density greater than Ar? __________

a. Cl₂ b. He c. NH₃ d. NO₂

Which of the following gases would have a higher rate of effusion than C₂H₂ ? _______

a. N₂ b. O₂ c. Cl₂ d. CH₄ e. CO₂

EXTRA CREDIT (4 points): Toy balloons are filled with hydrogen gas, at standard temperature, from a 10.0-liter cylinder. The initial pressure of the gas in the cylinder is exactly 100 atm. Assuming each balloon is filled to a volume of 1.0 liter at STP, how many balloons could be filled from this tank of gas? (NOTE: This problem may not as straight forward as it might at first seem!)