Question

Five stable isotopes of Kr are $^{80}Kr$ (2.6% by number of atoms), $^{82}Kr$ (11.6%), $^{83}Kr$ (11.5%), $^{84}Kr$ (57.0%) and $^{86}Kr$ (17.3%). Based on these data the average atomic mass of krypton calculated to three decimal point is x. Find value of 1000x.

Answer 1

83895

Answer 2

The average atomic mass is given by the weighted sum:

$\text{Average atomic mass} = (0.026 \times 80) + (0.116 \times 82) + (0.115 \times 83) + (0.57 \times 84) + (0.173 \times 86)$

Calculating each term:

$0.026 \times 80 = 2.08$

$0.116 \times 82 = 9.512$

$0.115 \times 83 = 9.545$

$0.57 \times 84 = 47.88$

$0.173 \times 86 = 14.878$

Summing these:

$\text{Average atomic mass} = 2.08 + 9.512 + 9.545 + 47.88 + 14.878 = 83.895 \, \text{amu}$

Since the average atomic mass $x = 83.895$ (to three decimal points), we have:

$1000x = 1000 \times 83.895 = 83895$