A 5% solution (by mass) of cane sugar in | Class 12 Chemistry Chapter Solutions, Solutions NCERT Solutions

Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter Solutions. This page offers a step-by-step solution to the specific question from Exercise 2, Question 20: . With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.

Question 20:

A 5% solution (by mass) of cane sugar in water has freezing point of 271 K. Calculate the freezing point of 5% glucose in water if freezing point of pure water is 273.15 K.

Answer:

In case of cane sugar:

ΔTf = (273.15 - 271) K = 2.15 K

Molar mass of sugar (C12H22O11) = 12 × 12 + 22 × 1 + 11 × 16 = 342 g mol - 1

5% solution (by mass) of cane sugar in water means 5 g of cane sugar is present in (100 - 5)g = 95 g of water.

Now, number of moles of cane sugar =5/342 mol

= 0.0146 mol

Therefore, molality of the solution,m =0.0146mol / 0.095kg 

= 0.1537 kg mol - 1

Now applying the relation,

ΔTf = Kf × m

⇒ Kf =  ΔTf  / m

 ⇒  2.15K / 0.1537 kg mol-1

= 13.99 K kg mol-1

Molar of glucose (C6H12O6) = 6 × 12 + 12 × 1 + 6 × 16 = 180 g mol - 1

5% glucose in water means 5 g of glucose is present in (100 - 5) g = 95 g of water.

∴ Number of moles of glucose = 5/180 mol

= 0.0278 mol

Therefore, molality of the solution, m =0.0278 mol / 0.095 kg

= 0.2926 mol kg - 1

Applying the relation,

ΔTf = Kf × m

= 13.99 K kg mol - 1 × 0.2926 mol kg - 1

= 4.09 K (approximately)

Hence, the freezing point of 5% glucose solution is (273.15 - 4.09) K= 269.06 K.


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Comments

  • Twinkle
  • Jul 17, 2020

Taugh but it makes it easy


  • Vivek
  • Nov 27, 2019

Nice answer


  • Krypton
  • Sep 09, 2019

Perfect answer


  • Abhinav priye
  • Apr 06, 2019

Very good 👍👍👍👍👌👌👌 Keep it up


  • Allin
  • Nov 20, 2018

Kf for water and sugar cane will be same for kf of water and glucose


  • Soumyanetra Basak
  • Jul 27, 2018

Good way


  • Prince Godwami
  • Jun 10, 2018

Perfect answer.


  • Vishal singh
  • Jun 05, 2018

Awesome


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Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 2 , Question 20: A 5% solution (by mass) of cane sugar in water has freezing point of 271 K. Calculate the freezing p....