Question

On a mission to a newly discovered planet, an astronaut finds chlorine abundances of 13.85 percent and 86.15percent forCl. What is the atomic mass of chlorine for this location? The mass of 35/Cl is 34.9700amu. The mass of 37/Cl is 36.9700amu.

The astronaut then measures the abundance of magnesium on the new planet, obtaining the following results: first row: isotope ,24Mg, 25Mg, 26 Mg. Second row : abundance(percent). 78.99, 10.00. 11.01. Third row; mass (amu) : 23.99 24.99 25.98. What is the atomic mass of magnesium for this planet?

Answer 1

1)

average atomicmass of Cl = (35-Cl mass*percentage + 37-Cl mass*percentage)/100

                     = (34.9700*86.15+36.9700*13.85)/100

                     = 35.2470 amu

2) average atomicmass of Mg = (24-mg mass*percentage + 25-Mg mass*percentage + 26-Mg mass*percentage)/100

           = (23.99*78.99+24.99*10.00+25.98*11.01)/100

                        = 24.31 amu