Solutions: Class 12 Chemistry Practice Questions

A food technology student is developing a sports drink. She dissolves a non-volatile, non-electrolyte carbohydrate (molar mass = 180 g mol⁻¹) in water to study its colligative properties before finalising the formulation.

A food technology student is developing a sports drink. She dissolves a non-volatile, non-electrolyte carbohydrate (molar mass = 180 g mol⁻¹) in water. She prepares Solution P by dissolving 9.0 g of this carbohydrate in 500 g of water, and Solution Q by dissolving 9.0 g of the same carbohydrate in 250 g of water.

(a) Calculate the boiling point elevation (ΔT_b) of Solution P. (K_b for water = 0.52 K kg mol⁻¹) [2 marks]

(b) Without further calculation, predict how the boiling point elevation of Solution Q compares with that of Solution P. Give one reason for your answer. [1 mark]

(c) The student later adds a small amount of NaCl (van't Hoff factor i = 2) to Solution Q to improve conductivity. State with reason whether the osmotic pressure of the resulting solution would increase, decrease, or remain the same compared to Solution Q (before NaCl addition), assuming volume remains constant. [1 mark]

A school chemistry club is studying the effect of dissolving different solutes in water for a science project. They dissolve glucose (non-electrolyte, molar mass = 180 g mol⁻¹) in water and measure the boiling point elevation. In a second experiment, they dissolve NaCl (molar mass = 58.5 g mol⁻¹) in water and observe a greater boiling point elevation for the same mass of solute in the same mass of solvent.

A school chemistry club is studying the effect of dissolving different solutes in water for a science project. They dissolve glucose (non-electrolyte, molar mass = 180 g mol⁻¹) in water and measure the boiling point elevation. In a second experiment, they dissolve NaCl (molar mass = 58.5 g mol⁻¹) in water and observe a greater boiling point elevation for the same mass of solute in the same mass of solvent.

(a) The students dissolve 18 g of glucose in 500 g of water. Calculate the boiling point elevation produced. (K_b for water = 0.52 K kg mol⁻¹) [2 marks]

(b) Explain why the same mass of NaCl produces a greater boiling point elevation than glucose under identical conditions of solvent and solute mass. [1 mark]

(c) State the van't Hoff factor (i) for glucose and for NaCl (assuming complete dissociation), and identify which colligative property is used to determine molar mass of a polymer in the laboratory and why. [1 mark]

A pharmaceutical company is developing an oral rehydration solution (ORS). A chemist dissolves 9.0 g of glucose (M = 180 g mol⁻¹) and 1.17 g of NaCl (M = 58.5 g mol⁻¹) in 500 g of water. Assume NaCl dissociates completely into Na⁺ and Cl⁻ ions. Kb for water = 0.52 K kg mol⁻¹.

A pharmaceutical company is developing an oral rehydration solution (ORS). A chemist dissolves 9.0 g of glucose (M = 180 g mol⁻¹) and 1.17 g of NaCl (M = 58.5 g mol⁻¹) in 500 g of water to prepare the ORS. Assume NaCl dissociates completely and Kb for water = 0.52 K kg mol⁻¹.

(a) Calculate the molality of glucose in the solution. [1 mark]
(b) Calculate the elevation in boiling point (ΔTb) of the ORS due to both solutes. [2 marks]
(c) The chemist observes that the actual boiling point elevation is slightly less than the calculated value. Give ONE reason for this observation. [1 mark]

A group of students dissolves 3.42 g of cane sugar (sucrose, molar mass = 342 g mol⁻¹) in 500 g of water during a food science project. They observe that the solution boils at a temperature slightly above 100°C.

A group of students is conducting a chemistry experiment in their school laboratory. They dissolve 3.42 g of cane sugar (sucrose, molar mass = 342 g mol⁻¹) in 500 g of water to prepare a sugar solution for a food science project. They notice that the solution boils at a temperature slightly higher than 100°C.

(a) Calculate the boiling point elevation (ΔTb) of the solution. (Kb for water = 0.52 K kg mol⁻¹) [2 marks]
(b) Why does the boiling point of the sugar solution increase compared to pure water? Give reason. [1 mark]
(c) If the students had used 3.42 g of NaCl (molar mass = 58.5 g mol⁻¹) instead of sucrose in the same amount of water, would the boiling point elevation be more or less than that obtained with sucrose? Give reason. [1 mark]

A chemist working in a beverage quality-control laboratory prepares two solutions at 298 K — Solution P (glucose in water) and Solution Q (urea in water) — and also handles solvent mixtures in the laboratory.

A chemist working in a beverage quality-control laboratory prepares two solutions at 298 K:

Solution P: 5 g of glucose (M = 180 g mol⁻¹) dissolved in 100 g of water.
Solution Q: 5 g of urea (M = 60 g mol⁻¹) dissolved in 100 g of water.

(a) Which solution, P or Q, will have the higher boiling point? Calculate the boiling point elevation (ΔT_b) for BOTH solutions and verify your answer numerically. (K_b for water = 0.52 K kg mol⁻¹) [2 marks]

(b) The chemist then mixes chloroform (CHCl₃) with acetone (CH₃COCH₃) in the laboratory. What type of deviation from Raoult's law will this mixture show? Give one reason. [1 mark]

(c) Define 'molality' as a measure of concentration. Why is molality preferred over molarity when studying colligative properties at different temperatures? [1 mark]

A sports drink manufacturer dissolves glucose (C₆H₁₂O₆, M = 180 g mol⁻¹) and sodium chloride (NaCl, M = 58.5 g mol⁻¹) separately in water to prepare two isotonic solutions at 37°C. The osmotic pressure of the glucose solution is found to be 8.21 atm. The NaCl solution is prepared to match this osmotic pressure exactly. (R = 0.0821 L atm K⁻¹ mol⁻¹, T = 310 K)

A sports drink manufacturer dissolves glucose (C₆H₁₂O₆, M = 180 g mol⁻¹) and sodium chloride (NaCl, M = 58.5 g mol⁻¹) separately in water to prepare two isotonic solutions at 37°C. The osmotic pressure of the glucose solution is found to be 8.21 atm. The NaCl solution is prepared to match this osmotic pressure exactly.

(a) Calculate the molar concentration of the glucose solution. (R = 0.0821 L atm K⁻¹ mol⁻¹, T = 310 K) [2 marks]

(b) If NaCl is assumed to dissociate completely in water, what is the molar concentration of the NaCl solution needed to produce the same osmotic pressure of 8.21 atm? [1 mark]

(c) The manufacturer claims that dissolving the same mass of NaCl produces a higher osmotic pressure than the same mass of glucose. Justify this claim. [1 mark]

A nurse in a hospital needs to prepare an intravenous (IV) drip solution that is isotonic with human blood plasma. Human blood plasma has an osmotic pressure of 7.65 atm at 310 K (normal body temperature). The nurse uses glucose (molar mass = 180 g mol⁻¹) to prepare the drip solution. (R = 0.0821 L atm K⁻¹ mol⁻¹)

A nurse in a hospital needs to prepare an intravenous (IV) drip solution that is isotonic with human blood plasma. Human blood plasma has an osmotic pressure of 7.65 atm at 310 K (normal body temperature). The nurse prepares a glucose solution (molar mass of glucose = 180 g mol⁻¹) for this purpose.

(a) Write the formula used to calculate osmotic pressure of a solution. Using this formula, calculate the molarity of the glucose solution that would be isotonic with blood plasma at 310 K. (R = 0.0821 L atm K⁻¹ mol⁻¹) (2 marks)

(b) What mass of glucose must be dissolved to prepare 500 mL of this isotonic glucose solution? (1 mark)

(c) If a patient is accidentally given a solution more concentrated than isotonic (hypertonic solution) intravenously, what will happen to the red blood cells? Name this phenomenon. (1 mark)

A mountaineer carries a bottle of water to a high-altitude camp where atmospheric pressure is significantly lower than at sea level, causing water to boil at only 82°C. To cook rice properly, the mountaineer dissolves 17.1 g of sucrose (C₁₂H₂₂O₁₁) in 500 g of water before heating.

A mountaineer carries a bottle of water to a high-altitude camp. At that altitude, the atmospheric pressure is significantly lower than at sea level, so the water boils at only 82°C. To cook rice properly, the mountaineer dissolves 17.1 g of sucrose (C₁₂H₂₂O₁₁) in 500 g of water before heating.

(a) Calculate the elevation in boiling point of the sucrose solution prepared by the mountaineer. Will the solution boil above or below 100°C at sea level? (Given: Molar mass of sucrose = 342 g mol⁻¹; Kb for water = 0.52 K kg mol⁻¹)

(b) Sucrose is a non-electrolyte. What is the value of the van't Hoff factor (i) for sucrose in this solution? Give one reason for your answer.

(c) At high altitude, even the sucrose solution boils at a temperature lower than 100°C. State the colligative property responsible for the elevation in boiling point and explain in one sentence why a solute elevates the boiling point of a solvent.

Which of the following correctly explains why acetic acid dissolved in benzene shows a van't Hoff factor (i) less than 1?

Which one of the following aqueous solutions will show the highest boiling point elevation?

Which of the following aqueous solutions has the lowest freezing point?

The vapour pressure of a solution of two liquids P and Q is found to be lower than the vapour pressure of either pure component. What type of deviation from Raoult's law does this solution show?

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

For a dilute aqueous solution of glucose, the van't Hoff factor (i) is:

Which of the following is a colligative property of a solution?

A 5% solution of urea (molar mass = 60 g mol⁻¹) is isotonic with a 3% solution of an unknown non-electrolyte. Calculate the molar mass of the unknown non-electrolyte.

The boiling point of a 0·500 molal aqueous solution of urea (a non-electrolyte) is found to be 100·256°C. Calculate the van't Hoff factor for urea. (Given: K_b for water = 0·512 K kg mol⁻¹)

A solution of chloroform (CHCl₃) and acetone (CH₃COCH₃) shows negative deviation from Raoult's law. Give one reason for this deviation. What type of azeotrope does such a solution form?

Calculate the depression in freezing point when 5 g of glucose (Molar mass = 180 g mol⁻¹) is dissolved in 250 g of water. (K_f for water = 1.86 K kg mol⁻¹)

A solution is prepared by dissolving 5.85 g of sodium chloride (NaCl) in 200 g of water. The boiling point of pure water is 100°C and the molal elevation constant (Kᵇ) for water is 0.512 K kg mol⁻¹. Assuming complete dissociation of NaCl, calculate the boiling point of the solution. (Molar mass of NaCl = 58.5 g mol⁻¹)

A solution is prepared by dissolving 1.85 g of a non-electrolyte solute in 90 g of water. The boiling point of this solution is 100.104°C. Calculate the molar mass of the solute. Additionally, state the effect on the boiling point elevation if the same mass of solute were dissolved in 45 g of water instead.

(Kb for water = 0.52 K kg mol⁻¹, B.P. of pure water = 100°C)

State Raoult's law for a solution containing a non-volatile solute. A solution is prepared by dissolving 1.8 g of glucose (molar mass = 180 g mol⁻¹) in 100 g of water. The vapour pressure of pure water at 298 K is 23.8 mm Hg. Calculate the vapour pressure of the solution and the lowering in vapour pressure.

The vapour pressure of pure liquid A at 25°C is 80 mm Hg and that of pure liquid B at the same temperature is 120 mm Hg. A solution is prepared by mixing 3 mol of A with 2 mol of B. Assuming the solution behaves ideally:
(i) Calculate the vapour pressure of the solution.
(ii) Calculate the mole fraction of B in the vapour phase above the solution.
(iii) State whether the solution shows positive deviation, negative deviation, or no deviation from Raoult's law, giving one reason.

2.4 g of a non-volatile, non-electrolyte solute is dissolved in 60 g of water. The solution boils at 100.52°C. Calculate the molar mass of the solute. (Kᵇ for water = 0.52 K kg mol⁻¹; boiling point of pure water = 100°C)

State Raoult's law for a solution of volatile liquids. The vapour pressures of pure liquids A and B at 298 K are 450 mmHg and 150 mmHg respectively. A solution is prepared by mixing 2 moles of A and 3 moles of B. Assuming ideal behaviour, calculate: (i) the mole fractions of A and B in the solution, (ii) the total vapour pressure of the solution.

A food technologist is studying the preservation properties of sugar solutions used in jam-making. She prepares two solutions — one of sucrose and one of glucose — and investigates their colligative properties.

A food technologist is studying the preservation properties of a sugar solution used in jam-making. She dissolves 171 g of sucrose (C₁₂H₂₂O₁₁, molar mass = 342 g mol⁻¹) in 1000 g of water and measures its boiling point elevation. She then compares this with a glucose solution prepared by dissolving 90 g of glucose (C₆H₁₂O₆, molar mass = 180 g mol⁻¹) in 500 g of water.

(a) Calculate the boiling point of the sucrose solution. [Given: Kb for water = 0.52 K kg mol⁻¹; boiling point of pure water = 100°C] (2 marks)

(b) The technologist claims that both solutions will show the same elevation in boiling point. Is her claim correct? Justify your answer with a calculation. (1 mark)

(c) She further notes that neither sucrose nor glucose solution deviates from Raoult's law ideally when concentrated. State the type of deviation these solutions are expected to show and give ONE reason. (1 mark)

A sports drink manufacturer claims that their new electrolyte drink has an osmotic pressure equal to that of human blood plasma (approximately 7.65 atm at 37°C). A quality-control chemist dissolves 2.85 g of a non-electrolyte organic solute in enough water to make 100 mL of solution at 37°C and measures its osmotic pressure as 7.65 atm. The drink, when mixed with a small amount of a volatile organic solvent, also shows a boiling point lower than that of pure water.

A sports drink manufacturer claims that their new electrolyte drink has an osmotic pressure equal to that of human blood plasma (approximately 7.65 atm at 37°C). To verify this, a quality-control chemist dissolves 2.85 g of the active organic solute (a non-electrolyte) in enough water to make 100 mL of solution at 37°C.

(a) Write the formula used to calculate osmotic pressure of a solution and identify each term. (1 mark)

(b) Calculate the molar mass of the organic solute, given that the osmotic pressure of the prepared solution is 7.65 atm. (R = 0.0821 L atm K⁻¹ mol⁻¹) (2 marks)

(c) The chemist also notices that the drink, when mixed with a small amount of a volatile organic solvent, shows a boiling point LOWER than that of pure water. Identify the type of deviation from Raoult's law shown and give ONE reason for it. (1 mark)

A nurse in a hospital pharmacy is preparing intravenous (IV) fluids. She has four saline solutions at 25°C:

Solution P: 0.9% (w/v) NaCl in water (normal saline)
Solution Q: 1.8% (w/v) NaCl in water
Solution R: 0.45% (w/v) NaCl in water
Solution S: 5.0% (w/v) glucose (M = 180 g mol⁻¹) in water

Assume NaCl is completely dissociated (i = 2) and glucose does not dissociate (i = 1). The osmotic pressure of blood plasma is approximately 7.7 atm at 25°C. (R = 0.082 L atm K⁻¹ mol⁻¹, Molar mass of NaCl = 58.5 g mol⁻¹)

A nurse in a hospital pharmacy is preparing intravenous (IV) fluids. She has four saline solutions at 25°C:

Solution P: 0.9% (w/v) NaCl in water (normal saline)
Solution Q: 1.8% (w/v) NaCl in water
Solution R: 0.45% (w/v) NaCl in water
Solution S: 5.0% (w/v) glucose (M = 180 g mol⁻¹) in water

Assume NaCl is completely dissociated (i = 2) and glucose does not dissociate (i = 1). The osmotic pressure of blood plasma is approximately 7.7 atm at 25°C. (R = 0.082 L atm K⁻¹ mol⁻¹, Molar mass of NaCl = 58.5 g mol⁻¹)

(a) Calculate the osmotic pressure of Solution Q (1.8% w/v NaCl). Show your working. (2 marks)
(b) The nurse must choose an isotonic solution — one whose osmotic pressure matches that of blood plasma (≈ 7.7 atm). Based on your answer to (a) and the data given, identify which solution (P, Q, R or S) is isotonic and justify your choice. (1 mark)
(c) What will happen to red blood cells (RBCs) if Solution Q is administered intravenously? Name the phenomenon. (1 mark)

A food technologist is developing a sports drink that must remain liquid even when stored at −3.72°C. She dissolves glucose or NaCl in water and studies the effect on freezing point.

A food technologist is developing a sports drink that must remain liquid even when stored at −3.72°C. She dissolves a calculated mass of glucose (C₆H₁₂O₆, molar mass = 180 g mol⁻¹) in 500 g of water. She also considers replacing glucose with NaCl (molar mass = 58.5 g mol⁻¹), assuming complete dissociation of NaCl into two ions.

(a) Calculate the mass of glucose that must be dissolved in 500 g of water so that the solution does not freeze at −3.72°C.
(Given: Kf for water = 1.86 K kg mol⁻¹)

(b) What mass of NaCl would produce the same freezing point depression (ΔTf = 3.72 K) in 500 g of water? (Assume complete dissociation; i = 2)

(c) In terms of colligative properties, explain why NaCl is more effective than glucose at lowering the freezing point, even when equal masses of each are dissolved.

Four aqueous solutions, each 0.1 mol kg⁻¹, are prepared in a school laboratory for a freezing point depression experiment: glucose (non-electrolyte), NaCl (strong electrolyte, complete ionisation), CaCl₂ (strong electrolyte, complete ionisation), and acetic acid (weak electrolyte, α = 0.02).

A school laboratory has four aqueous solutions prepared for a freezing point depression experiment. Each solution is 0.1 mol kg⁻¹. The solutions are:
(i) Glucose (C₆H₁₂O₆) — a non-electrolyte
(ii) Sodium chloride (NaCl) — strong electrolyte, assume complete ionisation
(iii) Calcium chloride (CaCl₂) — strong electrolyte, assume complete ionisation
(iv) Acetic acid (CH₃COOH) — weak electrolyte, partial ionisation (degree of ionisation α = 0.02)

(a) Calculate the van't Hoff factor (i) for each solution and arrange the four solutions in increasing order of their freezing point depression. (2 marks)
(b) Which solution will have the HIGHEST freezing point? Justify your answer in one sentence. (1 mark)
(c) The teacher notices that the experimentally observed freezing point depression for acetic acid is slightly higher than that calculated for a pure non-electrolyte at the same molality, but much lower than for NaCl. Explain why. (1 mark)