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NTA Abhyas JEE Main2020ChemistrySolutionsPractice

The amount (in grams) of sucrose ( mol .wt . = 342 g ) that should be dissolved in 100 g water in order to produce a solution with a 105.0 o C difference between the boiling point and freezing point is (Given that k ƒ = 1.86 K k g m o l – 1 and k b = 0.52 K k g m o l – 1 for water) Report your answer by rounding it up to the nearest whole number.

Correct answer

72

Step-by-step solution

Let the molality of the soluiton is m . ΔT f = K f × m and ΔT b = K f b × m ΔT f + ΔT b = ( K f + K b ) × m = ( 1.86 + 0.51 ) × m = 2.37 × m Hence, m = 5 2.37 = 2.11 and 2.11 × 100 1000 = 0.211 moles of sucrose must be dissolved in 100 gram of water. Required mass of sucrose = 0.211 mol × 342 g/mole = 72.2 g

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