Solutions — CBSE Class 12 board PYQs

Isotonic solutions have the same

Van't Hoff factor for Na${}_2$SO${}_4\cdot$10H${}_2$O solution, assuming complete ionization, is

Which of the following aqueous solutions will have the highest boiling point?

Identify which liquid will have a higher vapour pressure at 90°C if the boiling points of two liquids A and B are 140°C and 180°C respectively.

Define the term mole fraction.

Define osmotic pressure.

State the main advantage of molality over molarity as the unit of concentration.

State the condition resulting in reverse osmosis.

Give reason: when 30 mL of ethyl alcohol and 30 mL of water are mixed, the volume of resulting solution is more than 60 mL.

A and B liquids on mixing produce a warm solution. Which type of deviation is there and why?

Of 0.1 molal solutions of glucose and sodium chloride respectively, which one will have a higher boiling point?

What is the expected value of van't Hoff factor for K${}_3$[Fe(CN)${}_6$] in dilute solution?

Define mole fraction of a substance in a solution.

The liquids A and B boil at 145°C and 190°C respectively. Which of them has a higher vapour pressure at 80°C?

What are azeotropes? Give an example.

Define Henry's law about solubility of a gas in a liquid.

10 mL of liquid A was mixed with 10 mL of liquid B. The volume of resulting solution was found to be 19.9 mL. What do you conclude?

Why is the elevation in boiling point of water different in the following solutions?
i) 0.1 molar NaCl solution
ii) 0.1 molar sugar solution

Two liquids X and Y boil at 110°C and 130°C respectively. Which of them has higher vapour pressure at 50°C?

In the determination of molar mass of A${}^{+}$B${}^{-}$ using a colligative property, what may be the value of van't Hoff factor if the solute is 50% dissociated?

What would be the value of van't Hoff factor for a dilute solution of K${}_2$SO${}_4$ in water?

State the formula relating pressure of a gas with its mole fraction in a liquid solution in contact with it.

Which will have higher boiling point, 0.1 M NaCl or 0.1 M BaCl${}_2$ solution in water?

What is the sum of the mole fractions of all the components in a three component system?

Mention a large scale use of the phenomenon of reverse osmosis.

How is the molality of a solution different from its molarity?

Give an example of a solution containing a solid solute in a solid solvent.

How is it that the boiling points of the following solutions in water are different?
i) 0.1 M NaCl solution
ii) 0.1 M sugar solution

On mixing equal volumes of water and ethanol, what type of deviation would you expect from Raoult's law?

Solution A is obtained by dissolving 1 g of urea in 100 g of water and solution B is obtained by dissolving 1 g of glucose in 100 g of water. Which solution will have a higher boiling point and why?

Why is the cooking temperature in a pressure cooker higher than in the open pan?

When is the value of van't Hoff factor more than one?

For a 5% solution of urea (molar mass = 60 g/mol), calculate the osmotic pressure at 300 K. (R = 0.0821 L atm K${}^{-1}$ mol${}^{-1}$)

Visha took two aqueous solutions — one containing 7.5 g of urea (molar mass = 60 g/mol) and the other containing 42.75 g of substance Z, each in 100 g of water. It was observed that both the solutions froze at the same temperature. Calculate the molar mass of Z.

Calculate the mass of ascorbic acid (molar mass = 176 g mol${}^{-1}$) to be dissolved in 75 g of acetic acid to lower its freezing point by 1.5°C. (K${}_f$ = 3.9 K kg mol${}^{-1}$)

A 4% solution (w/w) of sucrose (M = 342 g mol${}^{-1}$) in water has a freezing point of 271.15 K. Calculate the freezing point of a 5% glucose (M = 180 g mol${}^{-1}$) solution in water. (Given: freezing point of pure water = 273.15 K)

i) Write the colligative property which is used to find the molecular mass of macromolecules.
ii) In a non-ideal solution, what type of deviation shows the formation of minimum boiling azeotropes?

Calculate the freezing point of a solution containing 60 g of glucose (molar mass = 180 g mol${}^{-1}$) in 250 g of water. (K${}_f$ of water = 1.86 K kg mol${}^{-1}$)

State Raoult's law for a solution containing volatile components. Write two characteristics of the solution which obeys Raoult's law at all concentrations.

Calculate the boiling point of a solution when 2 g of Na${}_2$SO${}_4$ (M = 142 g mol${}^{-1}$) was dissolved in 50 g of water, assuming Na${}_2$SO${}_4$ undergoes complete ionization. (K${}_b$ for water = 0.52 K kg mol${}^{-1}$)

Give reasons for the following:
(a) Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.
(b) Aquatic animals are more comfortable in cold water than in warm water.
(c) Elevation of boiling point …

What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ${\Delta }_{mix}H$ for positive deviation?

Define azeotropes. What type of azeotrope is formed by positive deviation from Raoult's law? Give an example.

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of the solute (associated or dissociated). (Given: molar mass of benzoic acid = 122 g mol${}^{-1}$, K${}_f$ for benzene = 4.9 K kg …

Differentiate between molality and molarity of a solution. What is the effect of change in temperature on molarity and molality values?

A solution prepared by dissolving 8.95 mg of a gene fragment in 35.0 mL of water has an osmotic pressure of 0.335 torr at 25°C. Assuming that the gene fragment is a non-electrolyte, calculate its molar mass.

What mass of NaCl (molar mass = 58.5 g mol${}^{-1}$) must be dissolved in 65 g of water to lower the freezing point by 7.5°C? The freezing point depression constant, K${}_f$, for water is 1.86 K kg mol${}^{-1}$. Assume the van't Hoff factor for NaCl is 1.87.

Define the terms 'osmosis' and 'osmotic pressure'. What is the advantage of using osmotic pressure as compared to other colligative properties for the determination of molar masses of solutes in solutions?

Non-ideal solutions exhibit either positive or negative deviations from Raoult's law. What are these deviations and why are they caused? Explain with one example for each type.

A decimolar solution of potassium ferrocyanide, K${}_4$[Fe(CN)${}_6$], is 50% dissociated at 300 K. Calculate the value of van't Hoff factor for potassium ferrocyanide.

A solution prepared by dissolving 1.25 g of oil of wintergreen (methyl salicylate) in 99.0 g of benzene has a boiling point of 80.31°C. Determine the molar mass of this compound. (B.P. of pure benzene = 80.10°C and K${}_b$ for benzene = 2.53°C kg mol${}^{-1}$)

What is meant by positive and negative deviations from Raoult's law, and how is the sign of ${\Delta }_{mix}H$ related to positive and negative deviations from Raoult's law?

Calculate the freezing point depression expected for a 0.05 m aqueous solution of Na${}_2$SO${}_4$. If this solution actually freezes at −0.320°C, what would be the value of van't Hoff factor? (K${}_f$ for water is 1.86 K kg mol${}^{-1}$)

Define the term osmotic pressure. Describe how the molecular mass of a substance can be determined on the basis of osmotic pressure measurement.

State Raoult's law for solutions of volatile liquid components. Taking a suitable example, explain the meaning of positive deviation from Raoult's law.

State Henry's law correlating the pressure of a gas and its solubility in a solvent and mention two applications of the law.

A solution containing 8 g of a substance in 100 g of diethyl ether boils at 36.86°C, whereas pure ether boils at 35.60°C. Determine the molecular mass of the solute. (For ether, K${}_b$ = 2.02 K kg mol${}^{-1}$)

Calculate the temperature at which a solution containing 54 g of glucose (C${}_6$H${}_{12}$O${}_6$) in 250 g of water will freeze. (K${}_f$ for water = 1.86 K kg mol${}^{-1}$)

The vapour pressure of water is 12.3 kPa at 300 K. Calculate the vapour pressure of a one molal solution of a non-volatile, non-ionic solute in water.

A 0.1539 molal aqueous solution of cane sugar (molar mass = 342 g mol${}^{-1}$) has a freezing point of 271 K while the freezing point of pure water is 273.15 K. What will be the freezing point of an aqueous solution containing 5 g of glucose (molar mass = 180 g mol${}^{-1}$) per 100 …

An antifreeze solution is prepared from 222.6 g of ethylene glycol (C${}_2$H${}_4$(OH)${}_2$) and 200 g of water. Calculate the molality of the solution. If the density of this solution is 1.072 g mL${}^{-1}$, what will be the molarity of the solution?

(a) A 4% solution of sucrose is isotonic with a 3% solution of an unknown organic substance. Calculate the molecular mass of the unknown substance.
(b) What is the mole fraction of the solute in a 2.5 m aqueous solution?

A 0.2 percent aqueous solution of a non-volatile solute exerts a vapour pressure of 1.004 bar at 100°C. What is the molar mass of the solute? (Given: vapour pressure of pure water at 100°C is 1.013 bar and molar mass of water is 18 g mol${}^{-1}$)

Give reasons for the following:
(a) When 30 mL of ethyl alcohol and 30 mL of water are mixed, the volume of the resulting solution is more than 60 mL.
(b) Copper is conducting as such while copper sulphate is conducting only in molten state or in aqueous solution.

(a) What are non-ideal solutions?
(b) What role does the molecular interaction play in deciding the vapour pressure of a solution of
(i) alcohol and acetone
(ii) chloroform and acetone?

(a) Urea forms an ideal solution in water. Determine the vapour pressure of an aqueous solution containing 10% by mass of urea at 40°C. (Vapour pressure of water at 40°C = 55.3 mm Hg)
(b) Why is the freezing point depression of 0.1 M sodium chloride solution nearly twice that of …

At 300 K, 36 g of glucose (C${}_6$H${}_{12}$O${}_6$) present per litre in its aqueous solution has an osmotic pressure of 4.98 bar. If the osmotic pressure of another solution of glucose is 1.52 bar at the same temperature, what would be its concentration?

(a) Why is the vapour pressure of a solution of glucose in water lower than that of water?
(b) A 6.90 M solution of KOH in water contains 30% by mass of KOH. Calculate the density of the KOH solution. (Molar mass of KOH = 56 g mol${}^{-1}$)

Calculate the osmotic pressure at 25°C and the freezing point of a 1.8% aqueous solution of glucose (C${}_6$H${}_{12}$O${}_6$). Assume ideal behaviour of the solution. Take density to be 1 g mL${}^{-1}$ and K${}_f$ for water to be 1.86 K kg mol${}^{-1}$. (R = 0.082 L atm mol${}^{-1}$ K${}^{-1}$)

State Henry's law for solubility of a gas in a liquid. Explain the significance of Henry's law constant (K${}_H$). At the same temperature, hydrogen is more soluble in water than helium. Which of them will have a higher value of K${}_H$ and why?

A solution is made by dissolving 30 g of a non-volatile solute in 90 g of water. It has a vapour pressure of 2.8 kPa at 298 K. At 298 K, the vapour pressure of pure water is 3.64 kPa. Calculate the molar mass of the solute.

2 g of benzoic acid (C${}_6$H${}_5$COOH) dissolved in 25 g of benzene shows a depression in freezing point equal to 1.62 K. Molal depression constant for benzene is 4.9 K kg mol${}^{-1}$. What is the percentage association of the acid if it forms a dimer in solution?

45 g of ethylene glycol (C${}_2$H${}_6$O${}_2$) is mixed with 600 g of water. Calculate:
(a) the freezing point depression,
(b) the freezing point of the solution. (K${}_f$ for water = 1.86 K kg mol${}^{-1}$; atomic masses: C = 12, H = 1, O = 16 u)

Calculate the osmotic pressure of a solution obtained by mixing 100 cm${}^3$ of 0.25 M solution of urea and 100 cm${}^3$ of 0.1 M solution of cane sugar at 293 K. (R = 0.082 L atm mol${}^{-1}$ K${}^{-1}$)

1.0 g of a non-volatile solute was dissolved in 100 g of acetone (molar mass = 58 g mol${}^{-1}$) at 298 K. The vapour pressure of the solution was found to be 192.5 mm Hg. Calculate the molar mass of the solute. (Vapour pressure of pure acetone at 298 K is 195 mm Hg)

An aqueous solution of sodium chloride freezes below 273 K. Explain the lowering in freezing point of water with the help of a suitable diagram.

When does the measurement of colligative properties of a solution lead to abnormal molecular masses? The freezing point depression of 0.1 m NaCl solution is 0.372°C. What conclusion would you draw about the molecular state of NaCl in the solution? (K${}_f$ for water is 1.86 K kg mo …

An aqueous solution containing 1.248 g of barium chloride (molar mass = 208.34 g mol${}^{-1}$) in 100 g of water boils at 100.0832°C. Calculate the degree of dissociation of barium chloride. (K${}_b$ of water = 0.52 K kg mol${}^{-1}$)

What is meant by van't Hoff factor? The osmotic pressure of a 0.0103 molar solution of an electrolyte is found to be 0.70 atm at 27°C. Calculate the van't Hoff factor. What conclusion do you draw about the molecular state of the solute in the solution? (R = 0.082 L atm mol${}^{-1}$ …

Explain why there is a rise in boiling point when a non-volatile solid is dissolved in a liquid. 0.90 g of a non-electrolyte was dissolved in 87.90 g of benzene. This raised the boiling point of benzene by 0.25°C. If the molecular mass of the non-electrolyte is 103 g mol${}^{-1}$, …

In a solution of urea, 3.0 g of it is dissolved in 100 mL of water. What will be the freezing point of this solution? State the approximation made, if any. (K${}_f$ for water = 1.86 K kg mol${}^{-1}$, molar mass of urea = 60 g mol${}^{-1}$)

"The solution of a non-volatile solute boils at a higher temperature than the pure solvent." Show this relationship on a graphic diagram.

A solution of 3.8 g of sulphur in 100 g of CS${}_2$ (boiling point 46.30°C) boils at 46.66°C. What is the formula of the sulphur molecule in this solution? (Atomic mass of sulphur = 32 g mol${}^{-1}$, K${}_b$ for CS${}_2$ = 2.40 K kg mol${}^{-1}$)

Calculate the number of moles of methanol in 5 litres of its 2 m solution, if the density of the solution is 0.981 kg L${}^{-1}$. (Molar mass of methanol = 32 g mol${}^{-1}$)

How is relative lowering of vapour pressure defined for a solution consisting of a volatile solvent and a non-volatile solute? How is this function related to the mole fraction of the solvent and of the solute?

Draw a suitable diagram to express the relationship for ideal solutions of A and B between vapour pressures and mole fractions of components at constant temperature.

The molal freezing point depression constant of benzene (C${}_6$H${}_6$) is 4.90 K kg mol${}^{-1}$. Selenium exists as a polymer of the type Se${}_x$. When 3.26 g of selenium is dissolved in 226 g of benzene, the observed freezing point is 0.112°C lower than that of pure benzene. Deduce …

For determining molar masses of macromolecular substances in solution, the osmotic pressure measurement method is preferred over measurement of any other colligative property. Give two reasons for it.

Give one example each of miscible liquid pairs showing positive and negative deviations from Raoult's law. Give one reason each for such deviations.

An aqueous solution of glucose is made by dissolving 10 g of glucose (C${}_6$H${}_{12}$O${}_6$) in 90 g of water at 303 K. If the vapour pressure of pure water at 303 K is 32.8 mm Hg, what would be the vapour pressure of the solution?

(a)(i) Ishan's automobile radiator is filled with 1.0 kg of water. How many grams of ethylene glycol (molar mass = 62 g mol${}^{-1}$) must Ishan add to get the freezing point of the solution lowered to −2.8°C? (K${}_f$ for water = 1.86 K kg mol${}^{-1}$)
(ii) What type of deviation fro …

(b)(i) The boiling point of water at 750 mm Hg pressure is 99.68°C. How much sucrose (molar mass = 342 g mol${}^{-1}$) is to be added to 500 g of water so that it boils at 100°C? (K${}_b$ for water = 0.52 K kg mol${}^{-1}$)
(ii) State Henry's law and write any one application of it.

(i) Why is the boiling point of 1 M NaCl solution more than that of 1 M glucose solution?
(ii) A non-volatile solute 'X' (molar mass = 50 g mol${}^{-1}$), when dissolved in 78 g of benzene, reduced its vapour pressure to 90%. Calculate the mass of X dissolved in the solution.
(iii) …

(i) Why is the value of van't Hoff factor for ethanoic acid in benzene close to 0.5?
(ii) Determine the osmotic pressure of a solution prepared by dissolving 2.32 × 10${}^{-2}$ g of K${}_2$SO${}_4$ in 2 L of solution at 25°C, assuming that K${}_2$SO${}_4$ is completely dissociated. (R = 0. …

(a) A 10% solution (by mass) of sucrose in water has a freezing point of 269.15 K. Calculate the freezing point of a 10% glucose solution in water, if the freezing point of pure water is 273.15 K. (Given: molar mass of sucrose = 342 g mol${}^{-1}$, molar mass of glucose = 180 g mol …

(a) 30 g of urea (M = 60 g mol${}^{-1}$) is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if the vapour pressure of pure water at 298 K is 23.8 mm Hg.
(b) Write two differences between ideal solutions and non-ideal solutions.

a) Calculate the freezing point of the solution when 1.9 g of MgCl${}_2$ (M = 95 g mol${}^{-1}$) was dissolved in 50 g of water, assuming MgCl${}_2$ undergoes complete ionization. (K${}_f$ for water = 1.86 K kg mol${}^{-1}$)
b) i) Out of 1 M glucose and 2 M glucose, which one has a higher …

a) When 2.56 g of sulphur was dissolved in 100 g of CS${}_2$, the freezing point lowered by 0.383 K. Calculate the formula of sulphur (S${}_x$). (K${}_f$ for CS${}_2$ = 3.83 K kg mol${}^{-1}$, atomic mass of sulphur = 32 g mol${}^{-1}$)
b) Blood cells are isotonic with 0.9% sodium chloride s …

(a) State Raoult's law for a solution containing volatile components. How does Raoult's law become a special case of Henry's law?
(b) 1.00 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. Find the molar mass of the solute …

(a) Define the following terms:
i) Ideal solution
ii) Azeotrope
iii) Osmotic pressure
(b) A solution of glucose (C${}_6$H${}_{12}$O${}_6$) in water is labelled as 10% by weight. What would be the molality of the solution? (Molar mass of glucose = 180 g mol${}^{-1}$)

a) List any four factors on which the colligative properties of a solution depend.
b) Calculate the boiling point of a one-molar aqueous solution of KBr (density 1.06 g mL${}^{-1}$). Given K${}_b$ for H${}_2$O = 0.52 K kg mol${}^{-1}$; atomic masses: K = 39, Br = 80.

a) Explain why a solution of chloroform and acetone shows negative deviation from Raoult's law.
b) Phenol associates in benzene to a certain extent to form a dimer. A solution containing 20 g of phenol in 1.0 kg of benzene has its freezing point lowered by 0.69 K. Calculate the f …

The freezing point depression constant for water is 1.86°C kg mol${}^{-1}$. If 5.00 g of Na${}_2$SO${}_4$ is dissolved in 45.0 g of H${}_2$O, the freezing point is changed by −3.82°C. Calculate the van't Hoff factor for Na${}_2$SO${}_4$.

a) Define the following terms:
i) Mole fraction
ii) van't Hoff factor
b) 100 mg of a protein is dissolved in enough water to make 10.0 mL of a solution. If this solution has an osmotic pressure of 13.3 mm Hg at 25°C, what is the molar mass of the protein?

a) What is meant by:
i) Colligative properties
ii) Molality of a solution
b) What concentration of nitrogen should be present in a glass of water at room temperature? Assume a temperature of 25°C, a total pressure of 1 atmosphere and mole fraction of nitrogen in air of 0.78. (K …