General Chemistry Answers

1.At 35.0 oC, the vapour pressure of pure ethanol (C2H5OH) is 100.0 mm Hg and the vapour pressure of pure acetone (CH3COCH3) is 360.0 mm Hg.

a) A solution is formed from 25.0 g of ethanol and 15.0 g of acetone. Assume ideal behaviour and calculate the vapour pressure of each component above this solution.

b) Calculate the mole fraction of acetone in the vapour in equilibrium with the solution in part a).

c) Name a method that can used to separate these two components in the lab.

2. How many ice cubes (at 0.0 oC) would you have to add to a 100.0 mL drink initially at 25.0 oC in order to lower its temperature to 4.0 oC? Each ice cube weighs 5.00 g, and the density of water is 1.00 g mL-1. Assume no heat loss. You may find some or all of the following constants useful:

Specific heat capacity of solid ice = 2.06 J g-1 oC-1; ΔHfusion = 6.02 kJ mole-1

Specific heat capacity of liquid water = 4.184 J g-1 oC-1; ΔHvap = 40.7 kJ mole-1

Specific heat capacity of water vapor = 1.84 J g-1 oC-1;

8. An ideal gas absorbs 1.00 x 103 J of heat and simultaneously expands against a constant external pressure of 1.10 atm from an initial volume of 10.0 L to a final volume of 35.0 L. Determine the expansion work (w) and change in internal energy (ΔU) for this process.

w = ΔU =

9. For the reaction (at 25 °C): N2(g) + O2(g) ⇌ 2NO(g) Kc = 4x10-31

Calculate the value of Kp (at 25 °C) for: NO(g) ⇌ ½ N2(g) + ½ O2(g)

10. If a steady current of 15.0 A is passed through an aqueous solution of CuSO4, how long will it take to deposit 0.100 mol of Cu at the cathode?

11. Rank the following species according to their relative strength as reducing agents. Rank the weakest reducing species as #1 and the strongest as #6.

___ Br-

___ H2O2 (acidic half-cell)

___ Ce3+

___ Cd

___ Li

___ Al

4. Which of the following solutions can NOT act as an effective buffer?

a) 50.0 mL 0.10M NH3 + 50.0 mL 0.10M NH4Cl

b) 50.0 mL 0.10 M HF + 50.0 mL 0.10 M NaF

c) 50.0 mL 0.10 M HBr + 50.0 mL 0.10 M NaOH

d) 50.0 mL 0.10 M HF + 30.0 mL 0.10 M KOH

e) 50.0 mL 0.10 M NH3 + 20.0 mL 0.10 M HCl

5. Which of the following mixtures is most likely to be an ideal solution?

a) NaCl and H2O

b) CH3CH2OH and C6H6

c) C7H16 and H2O

d) C7H16 and C8H18

e) None of the above.

6. Potassium hydroxide (KOH) is a strong base that is very soluble in water. Assuming complete dissociation, what is the pH of a 10.M solution of potassium hydroxide?

a) -1.00 b) 1.00 c) 13.00 d) 14.00 e) 15.00

7. How many electrons appear in the following half reaction when it is balanced?

MnO4- → Mn2+

a) 1 b) 2 c) 3 d) 4 e) 5

The degree of ionization of a weak acid such as acetic acid:

a) increases on dilution

b) increases upon addition of the salt, e.g., sodium acetate

c) is independent of solvent

d) is independent of temperature

e) increases upon addition of a strong acid

2. If the triple point pressure of a substance is greater than 1 atm, we expect

a) the solid to sublime without melting at 1 atm

b) the boiling point temperature to be lower than the triple point temperature

c) the melting point of the solid to come at a lower temperature than the triple point

d) that the substance cannot exist as a liquid

e) that the supercritical pressure would be less than 1 atm

3. Which of the following substances has the lowest standard molar entropy, So, at 298 K?

a) CO2(g) b) NaCI(s) c) CCI4(I) d) C(graphite) e) Hg(l)

How do you deduce the fractional atomic masses of elements from the relative isotopic abundance?

In the laboratory a gaseous compound of carbon and hydrogen contains 50% carbon by mass. The molar mass of the hydrogen carbon is 30.2g. Calculate bothe the emperical formula and molecular formula of hydrogen and carbon (c=12, H=1)gmol^-1

1)Consider an ideal gas that occupies 1000 mL at a pressure of 2.00 bar. If the gas is compressed

isothermally at a constant external pressure, Pext so that the final volume is 0.500 dm3

, what is the

smallest value Pext can have? Calculate the work involved using this value of Pext.�

An aqueous solution is made from 0.798 g of potassium permanganate, KMnO4. If the volume of solution is 50.0 mL, what is the molarity of KMnO4 in the solution?

(1 moL = 158.03 g KMnO4)

In the commercial manufacture of nitric acid, how many liters of nitrogen dioxide will produce 30 liters of nitric oxide given that both gases are at STP?

3NO₂ + H₂O  2HNO₃ +NO 

A. 20 liters 

B. 0.1 liters 

C. 40 liters 

D. 90 liters 

E. 1.01 liters