Gujarat BoardEnglish MediumSTD 9ScienceModel Paper 62 Marks
Question
Explain why chlorine, whether as the element or its compounds, always has a relative atomic mass of about 35.5.
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Answer
The relative atomic mass is the average mass of the naturally occurring stable isotopes of an element Chlorine exist as two stable isotopes i.e. ${ }^{35} Cl$ and ${ }^{37} Cl$ in ratio $3: 1$ respectively. Therefore Relative atomic mass of chlorine is taken as average of both stable isotopes. Natural chlorine always contains about $\frac{3}{4} \times{ }_{17}^{33} Cl$ and $\frac{1}{4} \times{ }_{17}^{37} Cl$ Therefore, relative atomic mass of chlorine $=\frac{3}{4} \times 35+\frac{1}{4} \times 37=35.5$
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