What are the normal freezing points and boiling points of the following solution

Question

What are the normal freezing points and boiling points of the following solutions? (a) 11.8 g NaCl in 183 mL of water (b) 13.9 g of urea in 68.8 mL of water

Explanation / Answer

moles NaCl = 11.8 g/58.44 g/mol=0.202 assuming density of water = 1 g/mL mass water = 183 mL x 1 g/mL = 183 g => 0.183 Kg molality = 0.202 / 0.183=1.104 i = vant'Hoff factor = 2 delta T = 1.86 x 2 x 1.104 =4.10 freezing point = 0 - 4.1 = - 4.1 °C delta T = 0.512 x 2 x 1.104 = 1.13 boiling point = 100 + 1.35 = 101.13 °C moles urea ( non electrolyte) = 13.9 g / 60.06 g/mol=0.231 m = 0.231 / 0.0688 Kg = 3.357 i = 1 delta T = 1.86 x 3.357 =6.24 °C freezing point = - 6.24 °C delta T = 0.512 x 3.357 =1.72 boiling point = 101.72 °C

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