Q17 / 160 · NTA Abhyas (NEET) 2020 · Chemistry · Solutions

 Urea (NH2-CO-NH2) needs to be dissolved in 100g of water, in order to decrease the vapour pressure of water by 25%. What will be the molality of the solution?

  • Correct answer
    A
    18.52 m
  • B
    62.45 m
  • C
    28.52 m
  • D
    35.64 m

Solution

p 0 − p S p 0  =  x Solute
= W Solute M Solute W Solute M Solute + W Solvent M Solvent
P0-PSP0=wAmA×mBWB (A stands for solute and B for solvent)
x-x×75100x×75100=w60×18100
[Let the vapour pressure of pure water, P0=x ]
0.25x0.75x=w60×18100
∴w=111.118
Molality= 111.11 60 × 1000 100 =18.52

Hence, the correct answer is option: 'A'.

More Solutions Questions