Question

The periodic table says that the average mass of copper is 63.55 but there is no such thing as copper-63.55. Why? (please use copper-63 and copper-64 in your answer)

Answer 1

69%for the isotope that weighs 62.93 u and

31

%

for the isotope that weighs 64.93 u.

You can approach this problem by using a single equation; let's say the first isotope contributes to the relative atomic mass by a fraction

x

(

x

<

1

). SInce there are only 2 isotopes to consider, the fraction the other isotope contributes with will automatically be

1

−

x

.

Let's set up the equation

x

⋅

62.93

u

+

(

1

−

x

)

⋅

64.93

u

=

63.55

u

Solving this for

x

will produce

64.93

u

−

63.55

u

=

2

x

→

x

=

1.38

2

=

0.69

Multiplying these fractions (0.69 and 1 - 0.69 = 0.31) by 100% percent to get the results as a percentage will give

69

%

for the isotpe that weighs 62.93u and

31

%

for the one that weighs 64.93u.

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