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Vinil7 [7]
2 years ago
14

"An aqueous CaCl2 solution has a vapor pressure of 83.1mmHg at 50 ∘C. The vapor pressure of pure water at this temperature is 92

.6 mmHg. What is the concentration of CaCl2 in mass percent?"
Chemistry
1 answer:
Lynna [10]2 years ago
4 0

Answer : The the concentration of CaCl_2 in mass percent is, 41.18 %

Solution : Given,

Molar mass of water = 18 g/mole

Molar mass of CaCl_2 = 110.98 g/mole

First we have to calculate the mole fraction of solute.

According to the relative lowering of vapor pressure, the vapor pressure of a component at a given temperature is equal to the mole fraction of that component of the solution multiplied by the vapor pressure of that component in the pure state.

\fac{p^o-p_s}{p^o}=X_B

where,

p^o = vapor pressure of the pure component (water) = 92.6 mmHg

p_s = vapor pressure of the solution = 83.1 mmHg

X_B = mole fraction of solute, (CaCl_2)

Now put all the given values in this formula, we get the mole fraction of solute.

\fac{92.6-83.1}{92.6}=X_B

X_B=0.102

Now we have to calculate the mole fraction of solvent (water).

As we know that,

X_A+X_B=1\\\\X_A=1-X_B\\\\X_A=1-0.102\\\\X_A=0.898

The number of moles of solute and solvent will be, 0.102 and 0.898 moles respectively.

Now we have to calculate the mass of solute, (CaCl_2) and solvent, (H_2O).

\text{Mass of }CaCl_2=\text{Moles of }CaCl_2\times \text{Molar mass of }CaCl_2

\text{Mass of }CaCl_2=(0.102mole)\times (110.98g/mole)=11.32g

\text{Mass of }H_2O=\text{Moles of }H_2O\times \text{Molar mass of }H_2O

\text{Mass of }H_2O=(0.898mole)\times (18g/mole)=16.164g

Mass of solution = Mass of solute + Mass of solvent

Mass of solution = 11.32 + 16.164 = 27.484 g

Now we have to calculate the mass percent of CaCl_2

Mass\%=\frac{\text{Mass of}CaCl_2}{\text{Mass of solution}}\times 100=\frac{11.32g}{27.484g}\times 100=41.18\%

Therefore, the the concentration of CaCl_2 in mass percent is, 41.18 %

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