Question

In a periodic table the average atomic mass of magnesium is given as 24.312 u. The average value is based on their relative natural abundance on earth. The three isotopes and their masses are 2412Mg(23.98504u), 2512Mg(24.98584u) and 2612Mg(25.98259u). The natural abundance of 2412Mg is 78.99% by mass. Calculate the abundances of other two isotopes.

Answer 1

Hey Dear,

◆ Answer -

Abundance of 12Mg25 = 9.30 %

Abundance of 12Mg26 = 11.71 %

● Explaination -

Let x be the abundance of 12Mg25. Then abundance of 12Mg26 would be 100-78.99-x = 21.01-x.

Average atomic mass of magnesium will be calculated as -

Average mass = [23.98504×78.99 + 24.98584×x + 25.98259×(21.01-x)] / 100

24.312 = (1894.578 + 24.98584x + 545.894 - 25.98259x) / 100

2431.2 = 2440.472 - −0.99675x

x = (2440.472 - 2431.2) / 0.99675

x = 9.30 %

Abundance of 12Mg25 = 9.30 %

Abundance of 12Mg26 = 21.01−9.30 %

Abundance of 12Mg26 = 11.71 %

Hope that helps you...