Vapour pressure of water is 360 …
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Payal Singh 6 years, 11 months ago
Vapour pressure of pure water, po = 360 mm Hg
Lowered vapour pressure, p = 360 –0 .5% of 360
= 360 – 1.8 = 358.2 mm Hg
Now, Weight of water, w1= 200ml x 1g.ml = 200g
Weight of urea w2 = ?
Molecular weight of water, M1 = 18 g/mol Molecular weight of urea, M2 = 60 g/mol
According to Roult’s law:
{tex}{p^o -p \over p} = {n_2\over n_1 + n_2}{/tex}
=> {tex}{360 - 358.2\over 358.2} = { {w_2 \over M_2}\over {{w_1\over M_1 } + {w_2 \over M_2}}}{/tex}
=> {tex}0.005 = { {w_2 \over M_2}\over {{w_1\over M_1 } + {w_2 \over M_2}}}{/tex}
=> {tex}0.005 {\left ({w_1\over M_1 } + {w_2 \over M_2}\right )}= {w_2 \over M_2}{/tex}
=> {tex}0.005 \times {w_1\over M_1 } = {w_2 \over M_2} - 0.005\times {w_2 \over M_2}{/tex}
=> {tex}0.005 \times {w_1\over M_1 } =0.995\times {w_2 \over M_2}{/tex}
=> {tex}{0.005 \over 0.995} \times {w_1\times M_2\over M_1 } = {w_2 }{/tex}
=> {tex}{0.005 \over 0.995} \times {200\over 18 }\times 60 = {w_2 }{/tex}
=> w2 = 3.33g
Hence, 3.33g urea should be added
1Thank You