Answer:
21.8 torr
Explanation:
Mathematically, the relationship between the mole fraction of the solvent and the vapor pressure of the solution looks like this
Psol= Xsolvent * P°solvent where,
Psol - the vapor pressure of the solution
Xsolvent - the mole fraction of the solvent
P°solvent - the vapor pressure of the pure solvent
So, your goal here is to figure out how many moles of sodium chloride and of water you have in the solution.
To do that, use the two compounds' respective molar masses. For sodium chloride you'll have
292.5g * (1mol NaCl/58.44g) = 5.005 moles of NaCl
Same for water except you first have to convert to grams by multiplying by 1000
1000g * (1 mol H2O/18.015g) = 55.51 moles H2O
Now, the mole fraction of water is equal to the number of moles of water divided by the total number of moles present in the solution.
ntotal = nwater +nNaCl
ntotal = 55.51 + 5.005 = 60.515 moles
The mole faction of water will thus be
Xwater= 55.51 moles/60.515 moles = 0.917
This means that the vapor pressure of the solution will be
Psol= 0.917 * 23.8 torr = 21.8 torr
