Average Atomic Mass Practice

Remember: 

average atomic mass = Atomic mass = (rel.abundanceisotope 1 × massisotope 1) + (rel.abundanceisotope 2 × massisotope 2) + (rel.abundanceisotope 3 × massisotope 3)  + etc.

Remember: relative abundance = % abundance / 100
NOTE: all of the relative abundances should add up to 1 (or % abundances should add up to 100%)

Example:
Chlorine has 2 isotopes

35Cl     relative atomic mass = 34.969 amu       % abundance = 75.78%
37Cl     relative atomic mass = 36.966 amu       % abundance = 24.22%

So, 

average atomic mass of Cl = (34.969 amu)(75.78/100) + (36.966 amu)(24.22/100) = 35.45 amu

1

Calculate the average atomic mass of Mg if the naturally occurring isotopes are 24Mg, 25Mg and 26Mg. Their masses and abundances are as follows:

24Mg relative atomic mass = 23.985 amu % abundance = 78.70%
25Mg relative atomic mass = 24.986 amu % abundance = 10.13%
26Mg relative atomic mass = 25.983 amu % abundance = 11.17%

Show your work below. Include units in your answer (round it to 2 decimal places).

1

Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following relative atomic masses and % abundances in nature: 6.017 amu, 7.30% and 7.018 amu, 92.70%.

Show your work below. Include units in your answer (round it to 2 decimal places).

1

Calculate the average atomic mass of chromium.

Chromium –50 49.946 amu 4.350 %
Chromium –52 51.941 amu 83.80 %
Chromium –53 52.941 amu 9.500 %
Chromium –54 53.939 amu ? %

Show your work below. Include units in your answer (round it to 2 decimal places). Hint: Find the % abundance of the last isotope first.

1

Copper is made up of 2 isotopes. Its average atomic mass is 63.55 amu. One isotope mass a relative atomic mass of 62.94 amu and its % abundance is 69.347%. Find the average atomic mass of the SECOND ISOTOPE. Hint: what should be the % abundance of the second isotope?

Show your work below. Include units in your answer (round it to 2 decimal places).

Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following relative atomic masses and % abundances in nature: 6.017 amu, 7.30% and 7.018 amu, 92.70%.Show your work below. Include units in your answer (round it to 2 decimal places).

Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following relative atomic masses and % abundances in nature: 6.017 amu, 7.30% and 7.018 amu, 92.70%.

Show your work below. Include units in your answer (round it to 2 decimal places).