What will be the molality of the solution containing 18.25 g of HCl gas in 500 g of water?

(i) 0.1 m

(ii) 1 M

(iii) 0.5 m

(iv) 1 m

<p>This is a Multiple Choice Questions as classified in NCERT Exemplar</p><p>Option (D)</p><p>The number of moles is given by the following formula, </p><p>Moles =<span contenteditable="false"> <math> <mfrac> <mrow> <mrow> <mi mathvariant="normal">M</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">s</mi> <mi mathvariant="normal">s</mi> </mrow> </mrow> <mrow> <mrow> <mi mathvariant="normal">M</mi> <mi mathvariant="normal">o</mi> <mi mathvariant="normal">l</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">r</mi> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">m</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">s</mi> <mi mathvariant="normal">s</mi> </mrow> </mrow> </mfrac> </math> </span> &nbsp;…. (1)</p><p>The number of moles of HCl is calculated by using equation (1) as follows, </p><p>Moles of HCl <span contenteditable="false"> <math> <mi mathvariant="normal"> </mi> <mo>=</mo> <mfrac> <mrow> <mrow> <mn>18.25</mn> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">g</mi> </mrow> </mrow> <mrow> <mrow> <mn>36.5</mn> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">g</mi> <mi mathvariant="normal"> </mi> <mo>/</mo> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">m</mi> <mi mathvariant="normal">o</mi> <mi mathvariant="normal">l</mi> </mrow> </mrow> </mfrac> </math> </span> 0.5 mol</p><p>The molality (m) is given by the formula:</p><p>m =<span contenteditable="false"> <math> <mfrac> <mrow> <mrow> <mi mathvariant="normal">n</mi> </mrow> </mrow> <mrow> <mrow> <mi mathvariant="normal">m</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">s</mi> <mi mathvariant="normal">s</mi> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">o</mi> <mi mathvariant="normal">f</mi> <mi mathvariant="normal"> </mi> <msup> <mrow> <mrow> <mi mathvariant="normal">s</mi> <mi mathvariant="normal">o</mi> <mi mathvariant="normal">l</mi> <mi mathvariant="normal">v</mi> <mi mathvariant="normal">e</mi> <mi mathvariant="normal">n</mi> <mi mathvariant="normal">t</mi> </mrow> </mrow> <mrow> <mrow> <mi mathvariant="normal">k</mi> <mi mathvariant="normal">g</mi> </mrow> </mrow> </msup> </mrow> </mrow> </mfrac> </math> </span></p><p>On substituting the values in the above equation:</p><p>Molality = <span contenteditable="false"> <math> <mfrac> <mrow> <mrow> <mn>0.5</mn> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">m</mi> <mi mathvariant="normal">o</mi> <mi mathvariant="normal">l</mi> <mi mathvariant="normal"> </mi> <mn>1000</mn> <mi mathvariant="normal"> </mi> <mi mathvariant="normal">k</mi> <mi mathvariant="normal">g</mi> </mrow> </mrow> <mrow> <mrow> <mn>500</mn> </mrow> </mrow> </mfrac> </math> </span> = 1m</p>

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