# How to find the relative atomic mass?

## Can somebody please explain to me how to do question 9? How am I gonnna the mass if I don't know anything? Please help!

Feb 19, 2017

Use the percentage abundances to calculate the weighted average (relative) atomic mass of the sample.

#### Explanation:

The Area under each peak is proportional to the relative concentration of that isotope. It can be approximated by the height of the peak for similarly-shaped peaks. Your measurement scale may be different from mine, but the ratios should be the same.

I have peak heights of 19, 2, 2 for each isotope respectively. Therefore,
.^(24)Mg = 19/23 = 0.826;
.^(25)Mg = 2/23 = 0.0870;
${.}^{26} M g = \frac{2}{23} = 0.0870 .$
These percentages are applied to the isotopic masses to find the “relative atomic mass” of the sample.
0.826 * 24 = 19.82 amu
0.087 * 25 = 2.18 amu
0.087 * 26 = 2.26 amu
The sum of these is the relative atomic mass of Mg in this sample. 24.26 g/mole.