exam3-ch89-gasesandsolutions1.pdf

Exam 3 – chap’2 8, 9 – gases and solutions Name: CHM 101

Select Response Write the letter of the best response in the blank. You will need the solubility curve and the rules. (12 pts)

__1. Identify the gas.

a. KCl b. NaCl c. NH3 d. NH4Cl

__2. What is the minimum temperature needed to dissolve 40.0 g of NH4Cl in 100 g of H2O?

a. 25 C b. 30 C c. 37 C d. 40 C

__3. What is the maximum mass of sodium nitrate that may be dissolved in 50.0 g of water at 37.0 C?

a. 32 g b. 37 g c. 52 g d. 87 g

__4. A student saturates 100 g of water with NaNO3, at 55 ºC then cools it to 40 ºC. What mass will be precipitated?

a. 14 g b. 22 g c. 105 g d. 119 g

__5. The following are solutions of soluble compounds at 0.10 M concentration. Which solution contains the greatest

number of ions?

a. 0.10 M NaCl b. 0.10 MFeCl3 c. 0.10 MCaCl2 d. 0.10 M KBr

__6. Which species is the precipitate if ammonium sulfate, (NH4)2SO4 is mixed with barium hydroxide, Ba(OH)2?

a. BaSO4 b. NH4OH c. Ba2SO4 d. all are soluble

Part II Brief Response Write the letter of the best response to each question in the table. (30 pt)

7. For an ideal gas under constant volume, if the pressure is tripled, what happens to the Kelvin temperature?

8. What is the temperature at which all molecular motion is a minimum?

9. Which term is the force per unit area or collisions with the walls of the container?

10. A flask contains a mixture of nitrogen and oxygen gases at STP. If the partial pressure of the nitrogen is 40.0 kPa,

then what is the partial pressure of the oxygen?

11. A flask contains a 1.00 mole of neon gas and 2.00 moles of argon gas. If the total pressure of the gases is 5.0 atm,

then what is the partial pressure of the argon gas?

12. Rank the following gases high to low density.

CH4 CO He O2 SO2

13. Alex cooled a gas from 50.0ºC to 25.0ºC at constant volume. Which of the following decreased?

I. The molar mass of the gas

II. The distance between the molecules

III. The speed of the molecules

14. What volume of O2(g) is required to react with excess CS2(l) to produce 4.0 L of CO2(g) at STP?

CS2(l) + 3O2(g) → CO2(g) + 2SO2(g)

15. Jimmy fills a teakettle with water, and begins to heat the kettle. When the water boils, the kettle whistles.

Why does the kettle whistles (why does the steam leave the kettle)?

16. True/False – correct the false statements to make them true.

a. The distance between gas particles is very large compare with the size of the particles.

b. Gases diffuse from areas of high pressure to areas of low pressure.

c. Gases have vibrational, rotational and translational motion.

d. The pressure and volume of a gas are directly related when temperature is a constant.

17 – 18 Four identical 1-L flasks each contain the gases He, N2, CO2 and Rn. All are the same Temperature and Pressure.

17. In which flask do the particles have the highest average speed?

18. Which flask contains the greatest number of particles?

Part II Constructed Response Solve each problem. Neatly display all work, units and significant figures. (57 pt.)

19. a. Is sodium carbonate soluble or insoluble in water? (1 pt)

b. A sample of the sodium carbonate is placed in water. Write the formula of what is present in the water based upon the

solubility you listed in part–a. (3 pts)

20. For the following reactants, write the net ionic equation for the precipitation reaction that occurs: (8 pts)

K2SO4 + Ca(OH)2 → ???

Net ionic equation:

21. Dewey Study has acquired 4.87 grams of magnesium acetate, Mg(HCO3)2, and dissolved it in 100.0 mL of deionized

water. What is the molarity of this solution? (6 pts)

22. What is the final molarity when 29.29 mL of a 4.27 M solution is added to water until the volume is 172 mL? (4 pts)

23. How many moles of BaCl2 are needed to make 2.75 liters of a 0.576 M solution? (4 pts)

24. Dee’s feet are aching at the end of a long day. At home, he dissolves 26.0 g of Epsom salt, magnesium sulfate (MgSO4),

in 1.25 kg of water. What is the new boiling point of this solution? The kb for water is 0.52 °C∙kg/mol.

(i) Find the moles of solute. (2 pts)

(ii) Find the molality of the solution. (2 pts)

(iii) Calculate the change in boiling point. (2 pts)

(iv) What is the new boiling point? (2 pts)