Calculate the mass of a non-volatile sol | Class 12 Chemistry Chapter Solutions, Solutions NCERT Solutions

Q18.

Calculate the mass of a non-volatile solute (molar mass 40 g mol-1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.

Let the vapour pressure of pure octane be p10.

Then, the vapour pressure of the octane after dissolving the non-volatile solute is 80/100 p10 = 0.8 p10.

Molar mass of solute, M2 = 40 g mol - 1

Mass of octane, w1 = 114 g

Molar mass of octane, (C8H18), M1 = 8 × 12 + 18 × 1 = 114 g mol - 1

Applying the relation,

(p10 - p1) / p10    =  (w2 x M1 ) / (M2  x w1 )

⇒ (p10 - 0.8 p10) / p10    =  (w2 x 114 ) / (40  x 114 )

⇒ 0.2 p10 / p10   =  w2 / 40

⇒ 0.2 = w2 / 40

⇒ w2 = 8 g

Hence, the required mass of the solute is 8 g.

👍 0
👎 0
✍️ Add Answer
🚩 Report

Study Tips for Answering NCERT Questions:

NCERT questions are designed to test your understanding of the concepts and theories discussed in the chapter. Here are some tips to help you answer NCERT questions effectively:

  • Read the question carefully and focus on the core concept being asked.
  • Reference examples and data from the chapter when answering questions about Solutions.
  • Review previous year question papers to get an idea of how such questions may be framed in exams.
  • Practice answering questions within the time limit to improve your speed and accuracy.
  • Discuss your answers with your teachers or peers to get feedback and improve your understanding.

Important Questions & Answers

Why is this answer important for exams?

This question is important because it tests key concepts from the NCERT syllabus and is frequently asked in CBSE exams.

Which NCERT concept is used in this question?

This question is based on core NCERT concepts explained in the chapter and should be revised thoroughly before exams.

What is the correct answer to: Calculate the mass of a non-volatile solute (molar mass 40 g mol-1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.?

Let the vapour pressure of pure octane be p10.

Then, the vapour pressure of the octane after dissolving the non-volatile solute is 80/100 p10 = 0.8 p10.

Molar mass of solute, M2 = 40 g mol - 1

Mass of octan...

How do you solve Calculate the mass of a non-volatile solute (molar mass 40 g mol-1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%. step by step?

Step-by-step explanation:
• Let the vapour pressure of pure octane be p10
•
•
• Then, the vapour pressure of the octane after dissolving the non-volatile solute is 80/100 p10 = 0
• 8 p10

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.

Latest Blog Posts

Stay updated with our latest educational content and study tips

How to Build a Career in Data Analytics Without a Computer Science Degree

How to Build a Career in Data Analytics Without a Computer Science Degree

All businesses are gathering information on customers, products, employees, and expenditures, and someone must make decisions based on the data. That individual is the data analyst. Unlike many career changers imagine, the job is open to a broader cross-section of the population than a typical career change. A lot of working analysts trained in commerce, … Read more

Read More
Life Insurance vs Health Insurance: Why Families May Need Both

Life Insurance vs Health Insurance: Why Families May Need Both

Are often purchased, talked and planned as being a replacement for another. They aren’t. One safeguards your family’s income in your absence and the other safeguards your family’s savings in the event that someone becomes ill. An examination of what they do, what they do not do, and why they are missing it when one … Read more

Read More
Home Loan vs Savings: Compare the Costs Before Buying a Home

Home Loan vs Savings: Compare the Costs Before Buying a Home

Pay upfront, or pay off less and over time? The truth depends on four factors most consumers will never compare at the same time: the interest rate on the house loan, the interest rate on the savings account, the rate of home price appreciation, and the cost of renting the home until you actually buy … Read more

Read More
Business After 30 or a Stable Job: Which Path Should You Choose?

Business After 30 or a Stable Job: Which Path Should You Choose?

Thirty is when the question starts to get raised and you’re able to do something because you know you have the experience—you know you have the responsibility. Here are some ways to consider the choice based on a realistic assessment without idealizing either aspect. Restlessness is one of those things that appears in your early … Read more

Read More

Student Discussion

Pankaj
Class · · , · May 24, 2019
Give the complete & correct solution, immediately
👍 👎 Reply
Tanya
Class · · , · May 04, 2019
This solution is quite easy but this is not correct. The correct answer for this question is 10.
👍 👎 Reply
Tanya
Class · · , · May 04, 2019
This is quite easy but correct answer is 10
👍 👎 Reply
Bhagya
Class · · , · Apr 25, 2019
For the answer to be 10 , it should be equated with X of solute i.e.
((w1/M1)/(w1/M1)+(w2/M2))
👍 👎 Reply
Gautam
Class · · , · Apr 22, 2019
Correct is 10
👍 👎 Reply
Neha
Class · · , · Mar 28, 2019
But answer is 10
👍 👎 Reply
Neha
Class · · , · Mar 28, 2019
Give the correct solution
👍 👎 Reply
Renuka
Class · · , · Mar 10, 2019
Answer is right
👍 👎 Reply
Malavika Manish
Class · · , · Mar 09, 2019
The answer is wrong ....the correct answer should be done like given below
if vapour pressure of pure liquid is = Po
80 % of pure liquid Ps= 80×Po/100 = 0.8Po
Ps =Po × Xsolute
mass of solute = x gram
mass of solvent = 114g
Molar mass of solute= 40 g/mol
Molar mass of solvent (octane C8H18) = 114g/mol
Number of moles of solute = x/40 = 0.025x
Number of moles of solvent = 114/114= 1 moles
Mole fraction of solvent = 1/(1+0.025x) 0.8Po=Po×1/(1+0.025x)
Cross multiply we get (1+0.025x))0.8Po= Po
Divide by 0.8 Po we get 1+0.025x = 1.25 Subtract 1 both side we get 0.025x = 0.25 Now divide by 0.025
we get
x = 10g
👍 👎 Reply
nikhil gupta
Class · · , · Jan 17, 2019
this answer in wrong instead the formula used will be p-ps/ps
👍 👎 Reply

ADD NEW COMMENT

        Can’t find your school? Type full name and submit.