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1470 cm^3 of a gas is collected over water at 303 K and 74.4 cm of Hg. If the gas weighs 1.98 g and vapour pressure of water at 30^@C is 3.2 cm of Hg, calculate the molecular weight of the gas.

Answer» <html><body><p><br/></p>Solution :The gas collected over water is wet. The pressure of the <a href="https://interviewquestions.tuteehub.com/tag/dry-960094" style="font-weight:bold;" target="_blank" title="Click to know more about DRY">DRY</a> gas can be obtained by subtracting the vapour pressure of water from the observed pressure of the wet gas. <br/> `:. ""P = 74.4 - 3.2 = 71.2 " cm Hg " (71.2)/<a href="https://interviewquestions.tuteehub.com/tag/76-335558" style="font-weight:bold;" target="_blank" title="Click to know more about 76">76</a>` atm <br/>`V = 1470 cm^3 = 1470/1000 = 1.47 L, T = 303K` <br/> If the <a href="https://interviewquestions.tuteehub.com/tag/molecular-562994" style="font-weight:bold;" target="_blank" title="Click to know more about MOLECULAR">MOLECULAR</a> weight of the gas is M, then the number of moles in 1.98 g of gas = `(1.98)/M` <br/>According to the gas equation `<a href="https://interviewquestions.tuteehub.com/tag/pv-593601" style="font-weight:bold;" target="_blank" title="Click to know more about PV">PV</a> = nRT`<br/> <a href="https://interviewquestions.tuteehub.com/tag/substituting-1231652" style="font-weight:bold;" target="_blank" title="Click to know more about SUBSTITUTING">SUBSTITUTING</a> the values, we have <br/>`(71.2)/76 xx 1.47 = (1.98)/M xx 0.0821 xx 303` <br/> `:. ""M = 35.8` <br/>Hence, the molecular weight of the given gas is 35.8.</body></html>


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