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Solutions - ISC Class 12 Chemistry Questions with Answers, Page 2

75 past-paper questions on Solutions from ISC Class 12 Chemistry papers (2027-2018), newest first, in full. Questions 21-40 are on this page, 20 to a page. Tap "Show answer" under a question to see its answer.

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2025 · 3 marks · Short answerOpen: The scientist van’t Hoff introduced a factor ( ) to account for the extent of…
The scientist van’t Hoff introduced a factor ($i$) to account for the extent of association or dissociation of solutes. It is mathematically expressed as: $i = \frac{\text{normal molecular mass}}{\text{experimental molecular mass}}$ In case of association, $i < 1$ and in case of dissociation $i > 1$.
(i)[1.5]
In the calculation of molecular mass of $\text{K}_4[\text{Fe}(\text{CN})_6]$ by using a colligative property, what will be the value of van’t Hoff factor if the solute is $25\%$ dissociated?
(ii)[1.5]
Find the value of van’t Hoff factor for a dilute aqueous solution of benzoic acid in water when it is completely associated to form a dimer.

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2025 · 3 marks · NumericalOpen: During a study trip, students visited a lake and took out water sample which…
During a study trip, students visited a lake and took out water sample which was rich in potassium chloride salt. They performed an experiment to calculate the boiling point of lake water which was found to be $100.025^\circ\text{C}$. If 500 g of the water sample was used for calculation ($K_b = 0.52\text{ K kg mol}^{-1}$) and there was 0.42 g KCl in the 500 ml sample, what is the observed molecular mass of KCl in the lake sample?

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2025 · 1 mark · MCQOpen: Depression in freezing point is a colligative property. At the same…
Depression in freezing point is a colligative property. At the same concentration in aqueous solution, select the solution that will show the largest freezing point depression.
  • (a)$\text{Na}_3\text{PO}_4$
  • (b)$\text{C}_{12}\text{H}_{22}\text{O}_{11}$
  • (c)$\text{NaCl}$
  • (d)$\text{K}_2\text{SO}_4$

No answer yet.

2025 · 5 marks · Short answerOpen: Answer the following questions: A solution of an organic compound is prepared…
Answer the following questions:
(a)[2.0]
A solution of an organic compound is prepared by dissolving $34\cdot2\text{ g}$ of solute in $500\text{ g}$ of water. Calculate the molecular mass of the solute and the freezing point of the aqueous solution. (Given: $K_b\text{ for water} = 0\cdot52\text{ K kg mol}^{-1}$, $K_f\text{ for water} = 1\cdot86\text{ K kg mol}^{-1}$ and boiling point of aqueous solution = $100\cdot104^\circ\text{C}$)
(b)[2.0]
Calculate the osmotic pressure of $10\%$ urea solution at $325\text{ K}$. (Given: Molecular mass of urea = $60\text{ g mol}^{-1}$, $R = 0\cdot0821\text{ L atm mol}^{-1}\text{ K}^{-1}$)
(c)[1.0]
A person suffering from high blood pressure is advised to take minimum quantity of common salt. Why?

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2025 · 5 marks · Short answerOpen: Osmosis and osmotic pressure play a very significant role in biological…
Osmosis and osmotic pressure play a very significant role in biological processes. The osmotic pressure of human blood is $8\cdot21\text{ atm}$ at $27^\circ\text{C}$. It is interesting to know that a $0\cdot91\%$ (mass/volume) solution of $\text{NaCl}$, known as saline water is isotonic with fluids inside the human red blood cells. In this solution, the blood corpuscles neither swell nor shrink. Therefore, medicines are mixed with saline water before being injected into the veins. Answer the following questions.
(a)[1.0]
What is an isotonic solution?
(b)[1.0]
How much glucose should be used per $100\text{ ml}$ (aqueous solution) for intravenous injection that is isotonic with blood at $27^\circ\text{C}$?
(c)[1.0]
What would be the osmotic pressure of blood if the temperature is $37^\circ\text{C}$?
(d)[1.0]
A pure $\text{NaCl}$ solution with salt concentration less than $0\cdot91\%$ (mass/volume) is hypertonic solution to human blood. Is this statement true or false? Give a reason.
(e)[1.0]
Name the disease caused by taking a lot of salt or salty food, which results in water retention in tissue cells causing puffiness or swelling.

No answer yet.

2025 · 1 mark · MCQOpen: Which one of the following statements are correct regarding the depression of…
Which one of the following statements are correct regarding the depression of freezing point? (P) The depression in freezing point is directly proportional to the amount of solute dissolved in solution. (Q) The depression in freezing point is inversely proportional to the amount of solute dissolved in solution. (R) Vapour pressure of the solution is more than that of pure solvent. (S) Vapour pressure of the solution is less than that of pure solvent.
  • (a)Only (P) and (S) are correct.
  • (b)Only (Q) and (R) are correct.
  • (c)Only (Q) and (S) are correct.
  • (d)Only (P) and (Q) are correct.

No answer yet.

2025 · 5 marks · Case basedOpen: Water phase change in soil causes severe damage to roads, canals, airport…
Water phase change in soil causes severe damage to roads, canals, airport runways and other buildings. The freezing point is an important indicator to judge whether the soil is frozen or not. It is found that the addition of salt can effectively reduce the frost heave of soil. The graphs given below show the change in freezing point with different concentrations of salt and water: Source: https://www.mdpi.com/2073-4441/12/8/2232 It is clear from the graphs that as water content is high, depression is less and as the salt concentration is high, depression is more.
Figure for this question
(a)[2.0]
2.1g $\text{CoCl}_3\cdot 6\text{NH}_3$ (molecular weight = 267.5) was dissolved in 100 g of water. The freezing point of the solution was $-0.584^\circ\text{C}$. Assuming 100% ionization of the complex salt having coordination number 6, what will be the formula of the complex. Given that: $K_f$ for water = $1.86\text{ K kg mol}^{-1}$.
(b)[1.5]
Which salt solution is the best for de-icing? 1% NaCl or 1% $\text{CaCl}_2$ [Atomic weight of Na= 23, Ca = 40, Cl = 35.5 a.m.u]
(c)[1.5]
Equimolal concentration of two different solutes X and Y undergoes dimerization and trimerization respectively in their respective solutions. What will be the ratio of observed lowering of vapour pressure in two cases?

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2025 · 3 marks · Short answerOpen: Vapour pressure plays an important role in calculating boiling point and the…
Vapour pressure plays an important role in calculating boiling point and the freezing point of solutions. In cold countries salt is sprinkled on the road whereas while boiling egg, salt is added in water. Both these processes help the cause.
(a)
Explain relative lowering of vapour pressure.
(b)
How adding salt to water help in boiling of egg?
(c)
Why is salt sprinkled on road during winters?

No answer yet.

2025 · 1 mark · MCQOpen: The osmotic pressure of a solution: (P) increases with an increase in number of…
The osmotic pressure of a solution: (P) increases with an increase in number of moles of solute. (Q) decreases with an increase in number of moles of solute. (R) increases at a higher temperature. (S) is dependent on the nature of solute. Which one of the following is correct?
  • (a)Only (P) and (Q) are correct
  • (b)Only (P) and (R) are correct
  • (c)Only (P) and (S) are correct
  • (d)Only (Q) and (S) are correct

No answer yet.

2025 · 1 mark · MCQOpen: Colligative properties of a solution are: (P) Independent of the nature of…
Colligative properties of a solution are: (P) Independent of the nature of solute (Q) Proportional to molecular mass of solute (R) Proportional to concentration of solute (S) Independent of the amount of solvent
  • (a)Only P and Q are correct
  • (b)Only P and R are correct
  • (c)Only P and S are correct
  • (d)Only Q and S are correct

No answer yet.

2025 · 5 marks · Short answerOpen: Answer the following: Calculate the boiling point of urea solution when of urea…
Answer the following:
(a)[2.0]
Calculate the boiling point of urea solution when $8\cdot0\text{ g}$ of urea is dissolved in $250\text{ g}$ of water. Boiling point of pure water is $373\text{ K}$. ($K_b\text{ of water} = 0\cdot52\text{ K kg mol}^{-1}$, molecular mass of urea = $60\text{ g mol}^{-1}$)
(b)[2.0]
Ethylene glycol is used as an antifreeze agent. Calculate the amount of ethylene glycol to be added to four kilogram of water to prevent it from freezing at $-6^\circ\text{C}$. ($K_f\text{ of water} = 1\cdot86\text{ K kg mol}^{-1}$) Assume that ethylene glycol ($\text{CH}_2\text{OH}\cdot\text{CH}_2\text{OH}$) does not dissociate or associate in aqueous solution.
(c)[1.0]
What will be the effect on the value of molality and molarity of a solution with change in temperature?

No answer yet.

2025 · 5 marks · Short answerOpen: Osmotic pressure is the external pressure which should be applied to stop the…
Osmotic pressure is the external pressure which should be applied to stop the flow of solvent into the solution when the two are separated by a semipermeable membrane. The osmotic pressure is a colligative property. Two solutions having the same osmotic pressure are called isotonic. If there are two solutions and one of them is of lower osmotic pressure, it is called hypotonic while the other is called hypertonic. Answer the questions given below:
(a)[1.0]
What will happen if red blood corpuscles are placed in a $5\%$ $\text{NaCl}$ solution which is a hypertonic solution?
(b)[1.0]
Show that osmotic pressure ($\pi$) is a colligative property.
(c)[2.0]
Calculate the amount of pressure required to stop osmosis of a solution when $40\text{ g}$ of $\text{Na}_2\text{SO}_4$ is added to $1\text{ L}$ of water at $298\text{ K}$. (Given: $\text{Na} = 23, \text{O} = 16, \text{S} = 32$ and $R = 0\cdot0821\text{ L atm K}^{-1}\text{ mol}^{-1}$)
(d)[1.0]
Briefly discuss the process of reverse osmosis followed to desalinate sea water and convert it into drinking water.

No answer yet.

2025 · 3 marks · NumericalOpen: A student X was doing an experiment by taking 0.15 g acetic acid in 40 g of…
A student X was doing an experiment by taking 0.15 g acetic acid in 40 g of benzene. He suddenly observed that the freezing point of the mixture is lowered by $0.40^\circ\text{C}$. Do you think that association of acetic acid has taken place? If yes, what will be degree of association ($K_f$ of benzene = $5.12\text{ K kg mol}^{-1}$)?

No answer yet.

2025 · 3 marks · Short answerOpen: The colligative properties are properties of solutions which depend only upon…
The colligative properties are properties of solutions which depend only upon the number of solute particles irrespective of their nature. These properties help to calculate the molecular weight of non-volatile, non-dissociating and non-associating solutes. If the solute dissociates or associates, we get abnormal molecular weights. To account for abnormal molecular weights of such solutes, van’t Hoff factor ($i$) was introduced.
(i)[2.0]
When $1\cdot90\text{ g}$ of benzoic acid is dissolved in $26\text{ g}$ of benzene, it causes a depression in freezing point by $1\cdot60\text{ K}$. The molal depression constant for benzene is $4\cdot8\text{ K kg mol}^{-1}$ and the molecular mass of benzoic acid is $122\text{ g mol}^{-1}$. Calculate the degree of association of benzoic acid if it forms dimer in solution.
(ii)[1.0]
Arrange the aqueous solution of the following compounds in the increasing order of value of van’t Hoff factor: Benzoic acid, Barium chloride, Urea

No answer yet.

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