Question

Calculate the mass of urea that should be dissolved in 221 g water at 35 C to produce a solution with the vapor pressure of 37.5 mmhg. At 35 C, Pnull water is 42.2 mmg.

Answer #1

**According to Raoult’s law:**

**P = Po*X(solvent)**

**37.5 = 42.2*X(solvent)**

**X(solvent) = 0.889**

**This is mole fraction of water**

**mass(water)= 221 g**

**number of mol of water,**

**n = mass of water/molar mass of water**

**=(221.0 g)/(18 g/mol)**

**= 12.28 mol**

**X(water) = n(water)/( n(water) + n(urea))**

**0.889 = 12.28 / ( 12.28+n(urea))**

**10.91+0.889*n(urea) = 12.28**

**0.889*n(urea) = 1.367**

**n(urea) = 1.539 mol**

**molar mass of urea = 60.06 g/mol**

**mass of urea = molar mass * number of moles**

**= 60.06 g/mol * 1.539 mol**

**= 92.4 g**

**Answer: 92.4 g**

Calculate the mass of urea that should be dissolved in 225 g of
water at 35°C to produce a solution with a vapor pressure of 37.3
mmHg. (At 35°C, P o water = 42.2 mmHg.)
Please Help! Thanks!

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