# Ans_Ex4 - Nielsen CHM1041 Answer to Exercise Set#4 1 Why does fresh water evaporate faster than seawater under the same conditions Many ionic

This preview shows pages 1–4. Sign up to view the full content.

Nielsen Bhaskar/PC/1713-O/J 2/05 1 CHM1041 Answer to Exercise Set #4 1. Why does fresh water evaporate faster than seawater under the same conditions? Many ionic species are dissolved in seawater, among the most abundant are Cl -1 , SO 4 -2 , HCO 3 -1 , Na +1 , Mg +2 , K +1 , and Cz +2 . Their presence effectively decreases the concentration of the solvent, H 2 O, and consequently fewer H 2 O, and consequently fewer H 2 O molecules are available at the surface for vaporization. 2. The concentrations of two solutions (nonvolatile, nonelectrolytic solutes) are as follows: No. 1, 5.0 g of ethylene glycol, , in 100 g of water; 262 C H O No. 2, 8.0 g of glucose, , in 100 g of water 61 26 C H O Which solution has the higher (a) vapor pressure, (b) boiling point, (c) freezing point? 2 Solution No. 1, 5.0g C H O in 100 g H O 1 5.0 0.081 62.1 mole C H O gx m o l eCHO g = 0.081 0.81 0.100 mole molality m C H O Kg == 2 Solution No. 2, 8.0 g C H O in 100 g H O 22 1 8.0 0.044 180 mole C H O m o l g = 0.044 0.44 0.100 mole molality m C H O Kg (a) Since both solutions contain non-volatile solutes relative to the H 2 O solvent, the vapor pressures of the solutions are dependent upon the concentration of H 2 O. Therefore, as the solute concentration increases, the solvent concentration decreases, and the vapor pressure decreases. Solution no. 2, 044 m C 6 H 12 O 2 , should have a greater pressure than solution no. 1, 0.81 m C 2 H 6 O 2 . (b) Boiling point elevation, T = k b m. The greater the molaity, m, of the novolatile solute, the greater the boiling point elevation, and the higher the boiling point temperature. The BP of solution no. 1 (0.81 m) should be greater than the BP of solution no. 2 (0.44 m). (c) Freezing point depression, T = k f m. The greater the molality of the solute, the greater the freezing point depression. The solution with the lower solute con-centration (no. 2, 0.44 m) should have the higher freezing point (no. 1, 0.81 m).

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Nielsen Bhaskar/PC/1713-O/J 2/05 2 3. What are the freezing and boiling points of a solution prepared by dissolving 10.0 g of gluose, , in 40.0 g ? 61 26 C H O 2 HO 1 cos 10.0 0.0556 180. mole C H O moles glu e g x mole C H O g == 2 0.0665 ln 1.39 0.0400 mole C H O molality so m Kg H O freezing point soln, FP: 1.86 1.39 2.59 f TK m C m xm ∆= = ° = ° C 0.00 - 2.59 - 2.59 FP C C C ° = ° boiling point soln, BP: 0.512 1.39 0.712 b m C m = ° = ° C 100.000 0.712 100.712 B PC C + ° C ° m 4. The freezing point of an aqueous solution of a nonelectrolyte is –0.160ºC. What would be the expected normal boiling point of the same solution? 2 ln 0.000 , -0.160 , 0.160 pure so FP C FP C T C = ° = since f 0.160 0.0860 1.86 f TC mm KC m ° = ° BP soln : 0.512 0.0860 0.0440 b m C m x m = ° = ° C 100.0000 0.0440 100.0440 B C + ° C
Nielsen Bhaskar/PC/1713-O/J 2/05 3 5 5. Arrange the following aqueous solutions in the expected order of decreasing freezing points: 42 2 0.01 m NaCl, 0.02 m MgSO , 0.01 m MgCl , 0.005 m KBr, 0.025m HCl, 0.015 m C H OH

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 12/12/2011 for the course CHM 2041 taught by Professor Staff during the Fall '09 term at Santa Fe College.

### Page1 / 8

Ans_Ex4 - Nielsen CHM1041 Answer to Exercise Set#4 1 Why does fresh water evaporate faster than seawater under the same conditions Many ionic

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online