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

Q20.

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.

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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What is the correct answer to: 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.?

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 ...

How do you solve 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. step by step?

Step-by-step explanation:
• In case of cane sugar:

• ΔTf = (273
• 15 - 271) K = 2
• 15 K

What common mistakes should be avoided in this question?

Students often lose marks by skipping steps, writing incomplete explanations, or misunderstanding keywords used in the question.

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Student Discussion

Twinkle
Class · · , · Jul 17, 2020
Taugh but it makes it easy
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Vivek
Class · · , · Nov 27, 2019
Nice answer
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Krypton
Class · · , · Sep 09, 2019
Perfect answer
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Abhinav priye
Class · · , · Apr 06, 2019
Very good 👍👍👍👍👌👌👌
Keep it up
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Allin
Class · · , · Nov 20, 2018
Kf for water and sugar cane will be same for kf of water and glucose
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Soumyanetra Basak
Class · · , · Jul 27, 2018
Good way
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Prince Godwami
Class · · , · Jun 10, 2018
Perfect answer.
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Vishal singh
Class · · , · Jun 05, 2018
Awesome
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