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A 1.0 m solution of HCl in benzene has a freezing point of 0.4 °C. Is HCl an electrolyte in benzene? Explain.

No. Pure benzene freezes at 5.5 °C, and so the observed freezing point of this solution is depressed by Δ T f = 5.5 − 0.4 = 5.1 °C. The value computed, assuming no ionization of HCl, is Δ T f = (1.0 m)(5.14 °C/ m ) = 5.1 °C. Agreement of these values supports the assumption that HCl is not ionized.

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A solution contains 5.00 g of urea, CO(NH 2 ) 2 , a nonvolatile compound, dissolved in 0.100 kg of water. If the vapor pressure of pure water at 25 °C is 23.7 torr, what is the vapor pressure of the solution?

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A 12.0-g sample of a nonelectrolyte is dissolved in 80.0 g of water. The solution freezes at −1.94 °C. Calculate the molar mass of the substance.

144 g mol −1

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Arrange the following solutions in order by their decreasing freezing points: 0.1 m Na 3 PO 4 , 0.1 m C 2 H 5 OH, 0.01 m CO 2 , 0.15 m NaCl, and 0.2 m CaCl 2 .

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Calculate the boiling point elevation of 0.100 kg of water containing 0.010 mol of NaCl, 0.020 mol of Na 2 SO 4 , and 0.030 mol of MgCl 2 , assuming complete dissociation of these electrolytes.

0.870 °C

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How could you prepare a 3.08 m aqueous solution of glycerin, C 3 H 8 O 3 ? What is the freezing point of this solution?

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A sample of sulfur weighing 0.210 g was dissolved in 17.8 g of carbon disulfide, CS 2 ( K b = 2.43 °C/ m ). If the boiling point elevation was 0.107 °C, what is the formula of a sulfur molecule in carbon disulfide?

S 8

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In a significant experiment performed many years ago, 5.6977 g of cadmium iodide in 44.69 g of water raised the boiling point 0.181 °C. What does this suggest about the nature of a solution of CdI 2 ?

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Lysozyme is an enzyme that cleaves cell walls. A 0.100-L sample of a solution of lysozyme that contains 0.0750 g of the enzyme exhibits an osmotic pressure of 1.32 × 10 −3 atm at 25 °C. What is the molar mass of lysozyme?

1.39 × 10 4 g mol −1

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The osmotic pressure of a solution containing 7.0 g of insulin per liter is 23 torr at 25 °C. What is the molar mass of insulin?

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The osmotic pressure of human blood is 7.6 atm at 37 °C. What mass of glucose, C 6 H 12 O 6 , is required to make 1.00 L of aqueous solution for intravenous feeding if the solution must have the same osmotic pressure as blood at body temperature, 37 °C?

54 g

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What is the freezing point of a solution of dibromobenzene, C 6 H 4 Br 2 , in 0.250 kg of benzene, if the solution boils at 83.5 °C?

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What is the boiling point of a solution of NaCl in water if the solution freezes at −0.93 °C?

100.26 °C

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The sugar fructose contains 40.0% C, 6.7% H, and 53.3% O by mass. A solution of 11.7 g of fructose in 325 g of ethanol has a boiling point of 78.59 °C. The boiling point of ethanol is 78.35 °C, and K b for ethanol is 1.20 °C/ m . What is the molecular formula of fructose?

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The vapor pressure of methanol, CH 3 OH, is 94 torr at 20 °C. The vapor pressure of ethanol, C 2 H 5 OH, is 44 torr at the same temperature.

(a) Calculate the mole fraction of methanol and of ethanol in a solution of 50.0 g of methanol and 50.0 g of ethanol.

(b) Ethanol and methanol form a solution that behaves like an ideal solution. Calculate the vapor pressure of methanol and of ethanol above the solution at 20 °C.

(c) Calculate the mole fraction of methanol and of ethanol in the vapor above the solution.

(a) X CH 3 OH = 0.590 ; X C 2 H 5 OH = 0.410 ; (b) Vapor pressures are: CH 3 OH: 55 torr; C 2 H 5 OH: 18 torr; (c) CH 3 OH: 0.75; C 2 H 5 OH: 0.25

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The triple point of air-free water is defined as 273.15 K. Why is it important that the water be free of air?

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Meat can be classified as fresh (not frozen) even though it is stored at −1 °C. Why wouldn’t meat freeze at this temperature?

The ions and compounds present in the water in the beef lower the freezing point of the beef below −1 °C.

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An organic compound has a composition of 93.46% C and 6.54% H by mass. A solution of 0.090 g of this compound in 1.10 g of camphor melts at 158.4 °C. The melting point of pure camphor is 178.4 °C. K f for camphor is 37.7 °C/ m . What is the molecular formula of the solute? Show your calculations.

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A sample of HgCl 2 weighing 9.41 g is dissolved in 32.75 g of ethanol, C 2 H 5 OH ( K b = 1.20 °C/ m ). The boiling point elevation of the solution is 1.27 °C. Is HgCl 2 an electrolyte in ethanol? Show your calculations.

Δ bp = K b m = ( 1.20 ° C / m ) ( 9.41 g × 1 mol Hg Cl 2 271.496 g 0.03275 kg ) = 1.27 ° C
The observed change equals the theoretical change; therefore, no dissociation occurs.

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A salt is known to be an alkali metal fluoride. A quick approximate determination of freezing point indicates that 4 g of the salt dissolved in 100 g of water produces a solution that freezes at about −1.4 °C. What is the formula of the salt? Show your calculations.

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Source:  OpenStax, Ut austin - principles of chemistry. OpenStax CNX. Mar 31, 2016 Download for free at http://legacy.cnx.org/content/col11830/1.13
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