Chapter 13 Calculations

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3.70
Cyclohexane has a freezing point of 6.50 ?C and a Kf of 20.0 ?C/m. What is the freezing point of a solution made by dissolving 0.540 g of biphenyl (C12H10) in 25.0 g of cyclohexane?
2.79
Paradichlorobenzene, C6H4Cl2, is a component of mothballs. A solution of 2.00 g in 22.5 g of cyclohexane boils at 82.39 ?C. The boiling point of pure cyclohexane is 80.70 ?C. Calculate Kb for cyclohexane.
108 g
Assuming complete dissociation of the solute, how many grams of KNO3 must be added to 275 mL of water to produce a solution that freezes at ?14.5 ?C? The freezing point for pure water is 0.0 ?C and Kf is equal to 1.86 ?C/m.

Express your answer to three significant figures and include the appropriate units.

88.7
At 55.0 ?C, what is the vapor pressure of a solution prepared by dissolving 60.2 g of LiF in 253 g of water? The vapor pressure of water at 55.0 ?C is 118 mmhg. Assume complete dissociation of the solute.
Express your answer to three significant figures and include the appropriate units.
0.146
The following table presents the solubilities of several gases in water at 25 ?C under a total pressure of gas and water vapor of 1 atm.

Gas Solubility (mM)
CH4 (methane) 1.30

Note that the solubilities are given in millimolar, rather than molar concentrations.

If the methane contained in 5.00 L of a saturated solution at 25 ?C was extracted and placed under STP conditions, what volume would it occupy?

k = 6.26×10^?4 mol/(L?atm)
Air is a mixture of gases that is about 78.0% N2 by volume. When air is at standard pressure and 25.0 ?C, the N2 component will dissolve in water with a solubility of 4.88×10?4 M. What is the value of Henry’s law constant for N2 under these conditions?
solubility = 1.27×10^?3 mol/L
As a scuba diver descends under water, the pressure increases. At a total air pressure of 2.61 atm and a temperature of 25.0 ?C, what is the solubility of N2 in a diver’s blood? [Use the value of the Henry’s law constant k calculated in Part A, 6.26×10?4mol/(L?atm).]
Assume that the composition of the air in the tank is the same as on land and that all of the dissolved nitrogen remains in the blood.
0.600 M
What is the molarity of a 10.5 % by mass glucose (C6H12O6) solution? (The density of the solution is 1.03 g/mL .) Express the molarity to three significant figures.
0.651 m
What is the molality of a 10.5 % by mass glucose (C6H12O6) solution? (The density of the solution is 1.03 g/mL .)
Express the molality to three significant figures.
1) mNaCl = 2.506×10^?2 m
2) ?NaCl = 4.512×10?4
3) percent by mass NaCl = 0.1463 %
4) parts per million NaCl = 1463 ppm
A 2.500×10?2 M solution of NaCl in water is at 20.0?C. The sample was created by dissolving a sample of NaCl in water and then bringing the volume up to 1.000 L. It was determined that the volume of water needed to do this was 999.3 mL . The density of water at 20.0?C is 0.9982 g/mL.

1) Calculate the molality of the salt solution.

2) Calculate the mole fraction of salt in this solution.

3) Calculate the concentration of the salt solution in percent by mass.

4) Calculate the concentration of the salt solution in parts per million.

1) 9.64 %
2) X = 2.51×10^?2
3) 1.35 M
4) 1.43 m
A solution was prepared by dissolving 24.0 g of KCl in 225 g of water.

1) Calculate the mass percent of KCl in the solution.

2) Calculate the mole fraction of the ionic species KCl in the solution

3) Calculate the molarity of KCl in the solution if the total volume of the solution is 239 mL.

4) Calculate the molality of KCl in the solution.

22.5 torr
Calculate the vapor pressure at 25?C of a solution containing 55.3 g ethylene glycol (HOCH2CH2OH) and 285.2 g water. The vapor pressure of pure water at 25?C is 23.8 torr .
Express the pressure in torrs to three significant figures.
?HOCH2CH2OH = 0.144
A solution containing ethylene glycol and water has a vapor pressure of 7.88 torr at 10?C. Pure water has a vapor pressure of 9.21 torr at 10?C. What is the mole fraction of ethylene glycol in the solution?
Express the mole fraction to three significant figures.
a
tert-Butyl alcohol is a solvent with a Kf of 9.10 ?C/m and a freezing point of 25.5 ?C. When 0.807 g of an unknown colorless nonelectrolyte liquid was dissolved in 11.6 g of tert-butyl alcohol, the solution froze at 15.3 ?C.
Which of the following is most likely the identity of this unknown liquid?

a) ethylene glycol (molar mass = 62.07 g/mol)
b) 1-octanol (molar mass = 130.22 g/mol)
c) glycerol (molar mass = 92.09 g/mol)
d) 2-pentanone (molar mass = 86.13 g/mol)
e) 1-butanol (molar mass = 74.12 g/mol)

1.48×10^4 g/mol
A protein subunit from an enzyme is part of a research study and needs to be characterized. A total of 0.165 g of this subunit was dissolved in enough water to produce 2.00 mL of solution. At 28 ?C the osmotic pressure produced by the solution was 0.138 atm. What is the molar mass of the protein?
Express answer to three significant figures.
Part A: 108g
Part B: i = 1.73
Part A
Assuming complete dissociation of the solute, how many grams of KNO3 must be added to 275 mL of water to produce a solution that freezes at ?14.5 ?C? The freezing point for pure water is 0.0 ?C and Kf is equal to 1.86 ?C/m.
Express your answer to three significant figures and include the appropriate units.

Part B
If the 3.90 m solution from Part A boils at 103.45 ?C, what is the actual value of the van’t Hoff factor, i? The boiling point of pure water is 100.00 ?C and Kb is equal to 0.512 ?C/m.

Psoln = 175 mmHg
The solvent for an organic reaction is prepared by mixing 70.0 mL of acetone (C3H6O) with 65.0 mL of ethyl acetate (C4H8O2). This mixture is stored at 25.0 ?C. The vapor pressure and the densities for the two pure components at 25.0 ?C are given in the following table. What is the vapor pressure of the stored mixture?

Compound Vapor pressure (mmHg) Density (g/mL)
acetone 230.0 0.791
ethyl acetate 95.38 0.900

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