UP Academic League of Chemical Engineering Students (UP ALCHEMES) Academics Affairs Committee Review and Tutorials Program, AY 2013-2014 Chem 16 Third Exam (SAMPLE EXAM)

I. True or False: Write TRUE if the statement correct. Otherwise, write FALSE. 1. Gases have relatively low viscosity. 2. The van der Waals equation, with respect to the Ideal Gas law, adjusts the measured pressure down by subtracting a

factor that accounts for intermolecular attractions. 3. The density of a gas is inversely proportional to its molar mass. 4. The valence and conduction bands of an insulator have no gap between them. 5. The liquid-gas line in a phase diagram ends at the triple point. 6. Surface tension is the energy required to increase the surface area by a unit amount. 7. The solubility of a solute is the minimum amount that dissolves in a fixed quantity of a particular solvent at a specified

temperature, given that excess solute is present. 8. When solute and solvent are volatile, the vapor pressure of each is not affected by the presence of the other. 9. A Lewis base is an electron pair acceptor. 10. Acidity increases as pH increases. 11. Water is a strong electrolyte due to autoionization. 12. In the Lewis acid-base definition, an acid is any species that accepts a lone pair to form a new bond in an adduct.

II. Multiple Choice 1. A 5.00-L balloon at 29 °C is placed in a freezer at −10 °C to decrease the effusion of helium through the balloon

walls. What is the volume of the balloon in the freezer, assuming no effusion takes place? A. 4.35 L B. 0.230 L C. 1.72 L D. 5.74 L

2. What is the total pressure of a gas mixture composed of 2.55 g He and 6.48 g Ne in a 15.0-L container at 17 °C? He: 4.003 g/mol; Ne: 20.1797 g/mol A. 0.0891 atm B. 1.52 atm C. 14.3 atm D. 0.592 atm

3. Aluminum metal and chlorine gas react according to the equation provided below. How many grams of aluminum are required to react with 30.0 L of Cl2 at 21 °C and 4.88 atm? 2 Al(s) + 3 Cl2(g) 2 AlCl3(s) Al: 25.981 g/mol A. 246 g B. 2.97 g C. 164 g D. 109 g

4. A sample of a gas has an average rate of effusion that is 2.07 times as fast as that of SF6. What is the molar mass of the gas? SF6: 146.05542 g/mol A. 34.1 g/mol B. 625 g/mol C. 302 g/mol D. 70.5 g/mol

5. Which of the following statements concerning ionic compounds is INCORRECT? A. CaI2 is more soluble in water than is CaBr2. B. RbCl is more soluble in water than is LiF. C. CaS has a higher melting point than KCl. D. NaCl has a lower melting point than CsCl.

6. Which statement about solids is not correct? A. Silicon carbide has a high melting point and is extremely hard. B. Molecular solids tend to be soft and have low melting points. C. Solid CaCl2 conducts electricity. D. Ionic solids are composed of positive and negative ions.

7. In which of the following pairs are the relative boiling points assigned INCORRECTLY?

A. O2 > NO B. CH3COOH > C4H10 C. CH3CH2OH>CH3OCH3 D. ICl > Br2

8. An end-centered orthorhombic unit cell has a cereal-box shape with atoms at each corner and on the face of two opposite ends. How many atoms are in a unit cell? A. 1 B. 4 C. 2 D. 10

9. When most gases dissolve in water, the process is exothermic. Which of the following best explains why this is true? A. A solute trapped in a liquid gives off heat. B. No energy is required to separate gas molecules. C. Gases need a lot of energy to separate the molecules in them. D. All gases react with water.

10. An 810-mL solution contains 7.50 × 102 grams of C2H5OH (ethanol) and 85.0 grams of C6H12O6 (glucose). What are the mole fraction and molality of glucose in the solution? A. 0.0282 and 0.629 m B. 0.0290 and 0.629 m C. 0.0281 and 0.565 m D. 0.972 and 19.5 m

11. The boiling point of an aqueous solution of a nonvolatile, nonelectrolyte is 101.0 °C. What is the freezing point of this solution? The freezing-point depression constant for water is 1.86 °C/m, and its boiling point elevation constant is 0.512 °C/m. A. –1.0 °C B. –1.95 °C C. 3.63 °C D. –3.63 °C

12. Which step of the solution process releases energy? A. attraction between the solvent and the solute B. breaking up the solvent C. increasing disorder of the solution D. breaking up the solute

13. A solution has a pOH of –0.47. Which of the following statements is the best? A. This is impossible because the pH ranges from 0 to 14. B. The solution has an [OH-] greater than 10.0 M. C. The solution has an [OH-] greater than 1 M. D. The solution has a pH of 13.53.

14. Which of the following acids is a polyprotic acid in aqueous solution? A. H2SO4

B. HCO2H C. NH4

+

D. HC2H3O2

15. Which of the following represents the weakest acid? A. An acid with a Ka = 1.8 x 10-4

B. An acid with a Ka = 6.3 x 10-5 C. An acid with a pKa = 2.85 D. An acid with a pKa = 7.54

16. Identify the Brønsted–Lowry base or bases in this equilibrium. NH3(aq) + HCO3

−(aq) ↔ NH4

+(aq) + CO3

2−(aq)

A. NH3(aq)

B. HCO3-(aq) and NH4

+(aq)

C. NH3(aq) and CO32-

(aq)

D. NH4+

(aq)

III. Problem Solving: 1. A 3.57 g sample of a KCl-KClO3 mixture is decomposed by heating and produces 119 mL O2(g), measured at 22.4 °C

and 738 mm Hg. What is the mass percent of KClO3 in the mixture? 2 KClO3(s) → 2 KCl(s) + 3 O2(g)

KClO3: 122.6 g/mol

2. Given the phase diagram of graphite given below:

a. What type of phase change would occur if the temperature was decreased to 2123ºC from 4000ºC and the

pressure was increased from 10 atm to 143 atm? b. If the pressure was decreased from 200000 atm to 15000 atm, and the temperature was increased from

4200ºC to 6000 ºC, what phase change would occur? c. How many different temperatures does carbon exist in equilibrium with its three phases?

3. An aqueous solution has 109.2 g KOH/L solution. The solution density is 1.09 g/mL. Your task is to use 100.0 mL of

this solution to prepare 0.250 m KOH. What mass of which component, KOH or H2O, would you add to the 100.0 mL of solution? KOH: 56.010 g/mol

4. A mixture of 1.00 g H2 and 8.60 g O2 is introduced into a 1.500 L flask at 25 °C. When the mixture is ignited, an

explosive reaction occurs in which water is the only product. What is the total gas pressure when the flask is returned to 25 °C? (The vapor pressure of water at 25 °C is 23.8 mm Hg).

5. A 50.00 g sample of a solution of naphthalene (C10H8(s)) in benzene (C6H6(l)) has a freezing point of 4.45 °C. Calculate the mass percent C10H8 and the boiling point of this solution. Kf benzene = 5.12 °C/m; Kb benzene = 2.53 °C/m; freezing point of benzene = 5.53 °C; boiling point of benzene = 80.10 °C; naphthalene: 128.2 g/mol