7.7.1 GASES

QUESTIONS

Section A

For each of the questions only one of the lettered responses (A – D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1. The contents, all at the same pressure, of three identical flasks are as follows:

Flask (a) contains 8 g CH₄ (g) at temperature T_a

Flask (b) contains 8 g C₂H₆ (g) at temperature T_b

Flask (c) contains 8 g C₃H₈ (g) at temperature T_c

(Relative atomic masses: H=1, C=12)

Which one of the following is a correct representation of the temperature of the three gases?

A T_a = T_b = T_c

B T_a >T_b > T_c

C T_c >T_b > T_a

D T_c >T_a > T_b

2. Assuming oxygen obeys the equation pV = nRT, which one of the following graphs correctly represents the relationship between the pressure of a fixed mass of oxygen and its volume at constant temperature?

$A B C D

P p p p

v v v v

3

Section B

Answer all questions in the spaces provided.

1 (a) State the Ideal Gas Equation, and use it to find the relative formula mass of a substance if, in an experiment, 0.3 g of it occupies 120 cm³ at 1 x 10⁵ Pa and 373 K.

pV = nRT or pV = mRT [1]

M

Substitution into equation [1]

77-78 [1] Inclusion of units, eg. “g” [-1]

[3]

(b) If the empirical formula of the substance is CH, what is its molecular formula and structure?

C₆H₆ [1] follow through error

[1]

(or Correct explanation of each [1] + [1])

[2]