Question

Part A

What is the relative atomic mass of a hypothetical element that consists of the following isotopes in the indicated natural abundances?

Isotope	Isotopic mass (amu)	Relative abundance (%)
1	81.9	12.2
2	84.9	15.0
3	88.9	72.8

Express your answer to three significant figures and include the appropriate units.

Part B

What is the relative atomic mass of the element that consists of the following isotopes in the indicated natural abundances?

Isotope	Isotopic mass (amu)	Relative abundance (%)
1	57.93	67.76
2	59.93	26.16
3	60.93	1.25
4	61.93	3.66
5	63.93	1.16

Answer 1

relative atomic mass = atomic mass of 1st isotope*abundance + atomic mass of 2nd isotope*abundance/100

partA

relative atomic mass = (81.9*12.2+84.9*15+88.9*72.8)/100

                                    = 8744.6/100   = 87.446amu

part-B

relative atomic mass = atomic mass of 1st isotope*abundance + atomic mass of 2nd isotope*abundance/100

relative atomic mass   = (57.93*67.76+59.93*26.16+60.93*1.25+61.93*3.66 + 63.93*1.16)/100

                                       = 5870/100    = 58.70amu >>>answer