Question

1. Find the average atomic mass for Li if 7.5% of Li atoms are 6Li with a mass of 6.0151223 amu and 92.5% are 7Li with a mass of 7.0160041 amu.

2. Find the average atomic mass for B if 19.9% of B atoms are 10B with a mass of 10.0129371 amu and 80.1% are 11B with a mass of 11.0093055 amu.
3. Find the average atomic mass for Cl if 75.78% of Cl atoms are 35Cl with a mass of 34.96885271 amu and 24.22% are 37Cl with a mass of 36.96590260 amu.
4. Find the average atomic mass for Mg if 78.99% of Mg atoms are 24Mg with a mass of 23.9850419 amu, 10.00% are 25Mg with a mass of 24.9858370 amu, and 11.01% are 26Mg with a mass of 25.9825930 amu.
5. There are 2 isotopes of copper that occur naturally; 63Cu and 65Cu. The 63Cu atoms have a mass of 62.929601 amu and the 65Cu atoms have a mass of 64.927794 amu. What is the percent natural abundance for each isotope?

Answer 1

To calculate the average atomic mass of an element, you multiply the mass of each isotope by its abundance and add them together. The given examples show how to calculate the average atomic mass for Li, B, Cl, Mg, and Cu, and determine the percent natural abundance of each isotope.

Step-by-step explanation:

When calculating the average atomic mass of an element, you need to multiply the mass of each isotope by its abundance (expressed as a decimal) and then add them together. Let's solve the given examples:

1. For Li, multiply the mass of 6Li by its abundance of 0.075, and multiply the mass of 7Li by its abundance of 0.925. Add these values together to find the average atomic mass of Li.
2. For B, use the same process, multiplying the mass of 10B by its abundance of 0.199, and the mass of 11B by its abundance of 0.801.
3. For Cl, multiply the mass of 35Cl by its abundance of 0.7578, and multiply the mass of 37Cl by its abundance of 0.2422.
4. For Mg, multiply the mass of 24Mg by its abundance of 0.7899, the mass of 25Mg by its abundance of 0.1, and the mass of 26Mg by its abundance of 0.1101.
5. For Cu, multiply the mass of 63Cu by its unknown abundance, and multiply the mass of 65Cu by its unknown abundance. Set up a system of equations using the given information to solve for the abundances of each isotope.

Using these methods, you can find the average atomic mass for each element and the percent natural abundance of each isotope.