a solution prepared by dissolving 66.0 g of urea (NH2)2CO in 950g of water had a density of 1.018g mL. Express the concentration of the urea in:
a. weight-percent
b. mole fraction
c. molarity
d..molality
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a solution prepared by dissolving 66.0 g of urea (NH2)2CO in 950g of water had a density of 1.018g mL. Express the concentration of the urea in:
a. weight-percent
b. mole fraction
c. molarity
d..molality
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Answer:
a) The weight-percent of solute is (100%) –1 (66.0 g) / (950 g) = 6.9%
The molar mass of urea is 60, so the number of moles is
(66 g) /(60 g mol–1) = 1.1 mol.
The number of moles of H2O is
(950 g) / (18 g mol–1) = 52.8 mol.
b) Mole fraction of urea:
(1.1 mol) / (1.1 + 52.8 mol) = 0.020
c) molarity of urea: the volume of 1 L of solution is
(66 + 950)g / (1018 g L–1)= 998 mL.
The number of moles of urea (from a) is 1.1 mol.
Its molarity is then
(1.1 mol) / (0.998 L) = 1.1 mol L–1.
d) The molality of urea is (1.1 mol) / (.066 + .950) kg = 1.08 mol kg–1.