HOLIDAY HOMEWORK -LOWER 6 SCIENCE 2009

1. a) i Define relative atomic mass.
ii. The relative atomic mass of X is 30.97. How many
times is an atom of X heavier than a carbon-12 atom?
iii. Sulphur exists naturally as a mixture of four isotopes
with relative abundance given below.

Relative atomic mass
Relative abundance(%)
31.97
95.02
32.97
0.75
33.96
4.21
35.96
0.02
Calculate the relative atomic mass of sulphur.
(6m)
b) An element Y is a gas at ordinary conditions. The density of
Y is 1.11 gdm-3 at temperature 25°C and pressure 86.1 kPa.
i) Starting with the Ideal Gas Equation, calculate the relative molecular mass of Y and identify the gas. ( 3m)
c) A mixture of gas contains two isotopes of hydrogen:
Hydrogen-1 and Hydrogen-2
20 dm3 (at s.t.p) of the gas mixture has a mass of 1.80g.
Calculate the percentage of Hydrogen-1 in the mixture. (3m)

2. An organic compound, A , has the following composition by mass:
C:17.8% , H:1.5% , Cl: 52.6%, F:28.1%0
The mass spectrum of the compound shows a peak with the highest m/e
value at 138.

a) Calculate the empirical formula of A.
b) Determine the molecular formula of A. ( 4)

3. An element X has 2 isotopes, 36X and 38X .The mass spectrum of X shows two groups of lines as given in the table below:
Group
m/e value
Relative abundance
A
36
38
0.7
0.3
B
72
74
76
x
y
z







a)Identify the ions responsible for each of the lines.
b) Calculate the values of x, y and z. (10)


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