Question

At 323k the vapour pressure of a solution containing 45g of a solute of relative molecular mass 180.55 in ethanol is 207.2mm of Hg . vapour pressure of pure ethanol at 323k is 219.8mm of Hg. Find the mass of ethanol used?

Answer 1

hi hello hi hello hi hello hi hello hi hello hi hello hi hello hi hello hi hello hi hello I want earn points

Answer 2

The mass of ethanol used is 0.644gm.

Given:-

Mass of Solute = 45g

Molar Mass of Solute = 180.55g

Vapour pressure of the solution = 207.2mm of Hg

Vapour pressure of pure ethanol = 219.8mm of Hg

To Find:-

The mass of ethanol used.

Solution:-

We can easily calculate the mass of ethanol used by using these simple steps.

As

Mass of Solute = 45g

Molar Mass of Solute = 180.55g

Vapour pressure of the solution (p) = 207.2mm of Hg

Vapour pressure of pure ethanol (po) = 219.8mm of Hg

According to the formula of Relative Lowering of Vapour pressure,

$\frac{po - p}{po} = xa$

$\frac{219.8 - 207.2}{219.8} = xa$

$\frac{12.6}{219.8} = xa$

$xa = 0.057$

$xa = \frac{na}{na + nb}$

By neglecting na from the denominator, we get

$xa = \frac{na}{nb}$

$nb = \frac{mass \: of \: solute}{molar \: mass \: of \: solute}$

$nb = \frac{45}{180.55}$

$nb =0 .25$

$na = 0.057 \times 0.25$

$na = 0.014$

Now,

$n = \frac{mass}{molarmass}$

$0.014 = \frac{m}{46}$

$m = 0.014 \times 46$

$m = 0.644$

Hence, the mass of ethanol used is 0.644gm.

#SPJ2