We can start by using the weighted average formula:
average atomic mass = (% abundance of isotope 1 x mass of isotope 1) + (% abundance of isotope 2 x mass of isotope 2)
We know that 75% of the carbon atom has a mass number of 12.9, so we can assign the following values:
% abundance of isotope 1 = 75%
mass of isotope 1 = 12.9
We also know that the remaining 25% of the atom has a mass number that is not known, so we can assign the following values:
% abundance of isotope 2 = 25%
mass of isotope 2 = x (unknown)
Plugging these values into the formula, we get:
12.7 = (0.75 x 12.9) + (0.25 x x)
Simplifying and solving for x, we get:
x = (12.7 - 0.75 x 12.9) / 0.25
x = 12.46
Therefore, the mass number of the carbon isotope which is 25% of the Carbon 12.7 atom is 12.46.
A carbon atom has a relative atomic mass of 12.7.
75% of the carbon atom has a mass number of 12.9, whilst the remaining 25% has a mass number which is not known.
Calculate the mass number of the carbon isotope which is 25% of the Carbon 12.7 atom. Give your answer to 2 decimal places.
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