Question

Naturally occurring magnesium has an atomic mass of 24.312 and consists of three isotopes. The major isotope is Mg24, natural abundance 78.99%, relative atomic mass 23.98504. The next most abundant isotope is Mg26, relative atomic mass 25.98259. The third most abundant isotope is Mg25 whose natural abundance is in the ratio of 0.9083 to that of Mg26. Find the relative atomic mass of Mg25.

Answer 1

Answer:

25.05533 amu

Explanation:

The formula for the calculation of the average atomic mass is:

$Average\ atomic\ mass=(\frac {\%\ of\ the\ first\ isotope}{100}\times {Mass\ of\ the\ first\ isotope})+(\frac {\%\ of\ the\ second\ isotope}{100}\times {Mass\ of\ the\ second\ isotope})+(\frac {\%\ of\ the\ third\ isotope}{100}\times {Mass\ of\ the\ third\ isotope})$

The % of Mg 24 = 78.99 %

Let the % of Mg 26 = x %

The % of Mg 25 = 0.9083 x%

Thus, 78.99 + x + 0.9083 x = 100

x = 11.01 %

% of Mg 25 = 10 %

Given that:

For first isotope:

% = 78.99 %

Mass = 23.98504 amu

For second isotope:

% = 11.01 %

Mass = 25.98259 amu

For third isotope:

% = 10 %

Mass = A amu

Average mass = 24.312 amu

Thus,  $24.312=\frac{78.99}{100}\times \:23.98504+\frac{11.01}{100}\times \:25.98259+\frac{10}{100}\times \:A$

A = 25.05533 amu