1:17

1:17 be able to calculate the relative atomic mass of an element (Aᵣ) from isotopic abundances

75% of chlorine atoms are the type ³⁵Cl (have a mass number of 35)

25% of chlorine atoms are of the type ³⁷Cl (have a mass number of 37)

In order to calculate the relative atomic mass (A_r) of chlorine, the following steps are used:

$A_r = \frac{( (35 \times 75) + (37 \times 25) )}{100}$

$A_r = 35.5$

Example question:

A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%.

Calculate the relative atomic mass (A_r) of bromine.

$A_r = \frac{( (79 \times 50.7) + (81 \times 49.3) )}{100}$

$A_r = 79.99$

Spec	Q'stion	Ans	MS
1:17	Jan '12 (2), Q 1 c	Answer	MkS
1:17	Jan '15 (1), Q 9 f	Answer	MkS
1:17	Jan '17 (1), Q 4 b	Answer	MkS
1:17	Jan '18 (2), Q 2 e	Answer	MkS
1:17	May '12 (1), Q 6 c ii	Answer	MkS
1:17	May '14 (1), Q 3 b	Answer	MkS
1:17	May '16 (2R), Q 5 a ii	Answer	MkS
1:17	May '17 (2), Q 2 d	Answer	MkS