Question

Which of the following substances has the lowest boiling point? C12H16 CH2Br2 Br2 ICl

How much energy in kJ will it take to melt 5.0 g of frozen Ar at -190^o C?

T/F if methane was at -50^o C it cannot be made to liquify at any pressure.

If H₂O at -1.0^o C and 1.0 atm has enough pressure applied to it, what phase change, if any, can occur?

	solid to liquid
	liquid to solid
	stays solid
	stays liquid What is the concentration in percent by mass when a solution is prepared by dissolving 8.00 g of NaCl into 70.0 g of water? What kind of solute gets more soluble as the temperature of the solvent decreases? The normal vapor pressure of water at 30o C is 31.82 mmHg. When 25.0 g of glucose (C6H12O6) are dissolved in 25.0 g of water at 30o C, what is the solution's vapor pressure? What is the freezing point of a solution made up of 150.0 g of benzene (normal fp=5.5o C, Kf=5.12 oC/m) with 0.200 moles of naphthalene dissolved in them?

Answer 1

A) Boiling point of Br2 is lowest among the list of compounds.

B) Heat required to melt frozen Ar = mdHf = 5 x 1.18/39.95 = 0.15 kJ

C) Methane at -50 oC cannot be liquified at any pressure : False

D) If H2O at -10C and 1 atm has enough pressure, phase change would be,

solid to liquid

E) Concentration of NaCl solution = (8/78) x 100 = 10.25%

F) solutes which on dissolution produces less heat then the energy required to break apart the solid show increased solubility as the temperature of the solvent increases. Such dissolution reactions are endothermic in nature.

G) moles of glucose = 25/180.156 = 0.14 mol

moles of water = 25/18 = 1.39 mol

mole fraction of water = 1.39/1.53 = 0.91

Vapor pressure of solution = mole fraction of water x normal vapor pressure = 0.91 x 31.82 = 28.95 mmHg

H) molality of naphthalene = 0.2mol/0.15kg = 1.33 m

dTf = i.Kf.m

      = 1 x 5.12 x 1.33

      = 6.81 oC

Freezing point of solution = 5.5 - 6.81 = -1.31 oC