Where applicable, you MUST show ALL work for full credit!!! 1. Calculate the vap

Question

Where applicable, you MUST show ALL work for full credit!!! 1. Calculate the vapor pressure of a solution prepared by mixing 35.0 grams of solid Na2SO with 375.0 grams of water at 25 °C. The vapor pressure of pure water at 25 °C is 23.76 torr. 2. Ethylene glycol is a non-volatile liquid (OHCH2CHzOH). If you make a solution that is 22% by mass of ethylene glycol in water, what is the vapor pressure of the solution (assume that Po (H2O) = 23.76 torr)? Do you expect this to be an ideal solution? why or why not? 3. If the vapor pressure of CO2 inside an unopened bottle of soda is 5.0 atm and there is 0.16 mol/L of dissolved CO2 in the soda itself, what is the Henry's Law constant for Co.? 4. The Henry's law constant (mol/L atm) for oxygen n blood is 3.74 X102 mol/L atm at body temperature, 37°C. Calculate the molar concentration of oxygen in blood for an alpine climber where the atmospheric pressure is 0.45 atm. Assume that air is 21% oxygen.

Explanation / Answer

1. No. of moles = mass/molar mass

The molar masses of Na2SO4 and water are 142 and 18 g mol-1, respectively.

The no. of moles of Na2SO4 = 35 g/142 g mol-1 = 0.2465 mol

The no. of moles of water = 375 g/18 g mol-1 = 20.8333 mol

The total no. of moles = 0.2465 + 20.8333 = 21.0798 mol

The mole fraction of water (Xwater) = no. of moles of water/total no. of moles

i.e. Xwater = 20.8333/21.0798 = 0.9883

Now, according to Roult's law: Pwater = Xwater * Powater

Here, Pwater = partial vapor pressure of water in the solution of aqueous solution of Na2SO4, Powater = vapor pressure of pure water

Therefore, Pwater = 0.9883 * 23.76 torr

i.e. Pwater = 23.48 torr

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