Question

0. 000 45) The concentration of urea in a solution prepared by dissolving 16 g of urea in 20 g of H2O is _% by mass. The molar mass of urea is 60.0 g/mol. A) 0.48 B) 0.44 C) 80 D) 0.80 E) 44 46) The concentration of a benzene solution prepared by mixing 11.0 g C6H6 with 38.0 g CCl4 is molal. A) 2.40 B) 3.71 C) 0.622 D) 0.508 E) 0.289 47) The mole fraction of He in a gaseous solution prepared from 3.0 g of He, 6.5 g of Ar, and 10.0 g of Ne is A) 0.20 B) 0.86 C) 0.75 D) 0.53 E) 0.66

Answer 1

45.

Mass of solute = 16 g of urea

mass of solvent = 20 g

total mass = mass of solute + mass of solvent = 16 + 20 = 36 g

% of solute = mass of solute / total mass x 100 = (16 g /36 g ) * 100 = 44%

46.

Mass of Benzene 11.00 g Molar Mass of Benzene Moles of Benzene 78.11 g/mol Mass of Benzene / Molar mass of Benzene 11.00 g 78.11 g/mol = 0.1408 mol Mass of solvent 38 g = 0.038 kg (CC14) Molality of solution Moles of Benzene - Mass of solvent in Kg 0.1408 mol = 0.0380 kg 3.71 molal

47.

Mass of He Molar Mass of Moles of = 3.00 g 4.000 g/mol Mass of gas / Molar mass 3.000 g 4.000 g/mol 0.750 mol = Mass of Ar Molar Mass of Moles of 6.50 g 39.950 g/mol Mass of gas/ Molar mass 6.500 g 39.950 g/mol 0.163 mol Mass of Ne Molar Mass of Moles of 10.00 g 20.180 g/mol Mass of Gas / Molar mass 10.000 8 20.180 g/mol 0.496 mol = Total moles Solution Total moles Solution = 4.2.682 mol 0.1627 + 0.750 + 1.4082 mol 0.4955 mol 0.1 Mole fraction He = = Moles of He /total moles 0.7500 1.4082 = 0.53