Final answer:
To find the average atomic mass of Lithium, convert the isotope abundances to decimals, multiply by their masses, and sum these products. The natural lithium average mass is 6.940934 amu, while for commercial lithium it is 6.977067 amu.
Step-by-step explanation:
To calculate the average atomic mass of Lithium, we use the known isotopic masses and their percent abundances. First, we must convert the percent abundances into decimal form by dividing by 100. Then multiply the decimal abundance by the mass of that particular isotope. Finally, sum the values obtained for each isotope to get the overall average atomic mass.
For natural lithium which has a composition of 7.5% 6Li (mass = 6.01512 amu) and 92.5% 7Li (mass = 7.01600 amu), the calculation would be as follows:
- (0.075 × 6.01512 amu) = 0.451134 amu
- (0.925 × 7.01600 amu) = 6.48980 amu
Adding these together: 0.451134 amu + 6.48980 amu = 6.940934 amu for the average atomic mass from natural sources.
If the lithium is from a commercial source with 3.75% 6Li, the calculation would be:
- (0.0375 × 6.01512 amu) = 0.225567 amu
- The remaining 96.25% is 7Li: (0.9625 × 7.01600 amu) = 6.75150 amu
Adding these together: 0.225567 amu + 6.75150 amu = 6.977067 amu for the average atomic mass from the commercial source.