Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.

Please verify your account before proceeding.

In this lesson, we will learn how to calculate percentage isotopic abundances from the relative atomic mass and isotopic masses.

Q1:

Chlorine has two stable isotopes, 3 5 C l and 3 7 C l , with atomic masses of 34.96885 u and 36.96590 u, respectively. The average atomic mass of naturally occurring chlorine is 35.453 u. Calculate to 4 significant figures the percentage abundance of 3 5 C l in naturally occurring chlorine.

Q2:

Magnesium has three stable isotopes, 2 4 M g , 2 5 M g and 2 6 M g , with atomic masses of 23.9850 u, 24.9858 u and 25.9826 u, respectively.

The natural abundances of 2 4 M g and 2 5 M g are 7 8 . 9 9 % and 1 0 . 0 0 % , respectively. Calculate the average atomic mass of magnesium.

The relative abundances of magnesium isotopes in a sample are 2 5 2 4 M g M g = 0 . 1 1 8 1 5 and 2 6 2 4 M g M g = 0 . 1 4 6 8 7 . Calculate to 4 significant figures the absolute abundance of 2 4 M g in the sample.

Q3:

Silicon has three stable isotopes, 2 8 S i , 2 9 S i and 3 0 S i , with atomic masses of 27.9769 u, 28.9765 u and 29.9738 u, respectively.

The natural abundances of 2 8 S i and 2 9 S i are 9 2 . 2 3 % and 4 . 6 8 % , respectively. Calculate to 4 significant figures the average atomic mass of silicon.

The relative abundances of silicon isotopes in a sample are 2 9 2 8 S i S i = 0 . 0 8 0 6 9 and 3 0 2 9 S i S i = 0 . 4 9 5 8 3 . Calculate to 4 significant figures the absolute abundance of 2 8 S i in the sample.

Q4:

Chlorine has two stable isotopes, 3 5 C l and 3 7 C l , with atomic masses of 34.9689 u and 36.9659 u, respectively. The relative abundance of 3 7 C l in an average sample of chlorine is 3 7 3 5 C l C l = 0 . 3 1 9 6 .

Calculate the average absolute abundance of 3 7 C l .

Calculate the average atomic mass of chlorine.

Q5:

Antimony has two stable isotopes, 1 2 1 S b and , with atomic masses of 120.9038 u and 122.9042 u, respectively. The relative abundance of in an average sample of antimony is 1 2 3 1 2 1 S b S b = 0 . 7 4 7 9 .

Calculate the average absolute abundance of 1 2 3 S b .

Calculate the average atomic mass of antimony.

Q6:

Gallium has two stable isotopes, 6 9 G a and 7 1 G a , with atomic masses of 68.9256 u and 70.9247 u, respectively.

Calculate to 3 significant figures the abundance of 7 1 G a for a sample of gallium with an average atomic mass 69.723 u.

Calculate to 3 significant figures the abundance of 6 9 G a for a sample of gallium with an average atomic mass of 69.620 u.

Q7:

Boron has two stable isotopes, 1 0 B and 1 1 B , with atomic masses of 10.0129 u and 11.0931 u, respectively.

Calculate to 3 significant figures the abundance of 1 0 B for a sample of boron with an average atomic mass of 10.807 u.

Calculate to 3 significant figures the abundance of 1 0 B for a sample of boron with an average atomic mass of 10.819 u.

Q8:

Copper has two stable isotopes, 6 3 C u and 6 5 C u , with atomic masses of 62.9296 u and 64.9278 u, respectively. The average atomic mass of naturally occurring copper is 63.546 u. Calculate to 4 significant figures the percentage abundance of 6 3 C u in naturally occurring copper.

Don’t have an account? Sign Up