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NCERT Class XI Chemistry Some Basic Concepts of Chemistry Solutions

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Question : 32 of 36
Marks: +1, -0
Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes :
Isotope Isotopic molar massAbundance
 36Ar\,{}^{36}\mathrm{Ar} 35.96755 g mol−1g\,\mathrm{mol}^{-1} 0.337 %
 38Ar\,{}^{38}\mathrm{Ar} 37.96272 g mol−1g\,\mathrm{mol}^{-1} 0.063 %
 40Ar\,{}^{40}\mathrm{Ar} 39.9624 g mol−1g\,\mathrm{mol}^{-1}99.600 %
Solution:  
Molar mass of naturally occurring argon isotopes
=
35.96755×0.337+37.96272×0.063+39.9624×99.6000.337+0.063+99.600\frac{35.96755\times 0.337+37.96272\times 0.063+39.9624\times 99.600}{0.337+0.063+99.600}
= 12.12+2.39+3980.255100\frac{12.12+2.39+3980.255}{100} = 3994.765100\frac{3994.765}{100} = 39.94 mol−1\mathrm{mol}^{-1}
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