Expressing Concentration - UNSOLVED PRACTICE SET

Q7. Define molarity and molality. Why does molarity change with temperature while molality does not?

Q8. Calculate the molarity of a solution containing 5.85 g of NaCl in 500 mL of solution.

[Given: Molar mass of NaCl = 58.5 g/mol]

Q9. A solution is prepared by dissolving 10 g of glucose (C₆H₁₂O₆) in 90 g of water. Calculate the mole fraction of glucose and water.

[Given: Molar masses: C₆H₁₂O₆ = 180 g/mol, H₂O = 18 g/mol]

Q10. Differentiate between molarity and normality. When are they numerically equal?

Q11. Your school chemistry lab has a bottle labelled "2 M H₂SO₄." Explain how you would prepare 250 mL of 0.5 M H₂SO₄ from this stock solution.

Q12. What is the relationship between molarity (M), molality (m), and density (d) of a solution? Derive the expression.

Q13. Discuss the various methods of expressing concentration of solutions:

(a) Mass percentage and volume percentage

(b) Molarity (M) — definition, formula, advantages, and limitations

(c) Molality (m) — definition, formula, advantages over molarity

(d) Mole fraction (x) — definition, properties, and significance

(e) Parts per million (ppm) and parts per billion (ppb)

For each method, give the formula and solve a numerical example.

Q14. Compare and contrast molarity and molality:

(a) Definitions and formulas

(b) Effect of temperature on each

(c) When to use molarity vs. when to use molality

(d) Derivation of the relationship between M, m, and density

(e) Numerical problems demonstrating interconversion between M and m

Q15. Concentration expressions are essential in Indian healthcare, agriculture, and industry. Discuss:

(a) Why saline drips in hospitals are specified as 0.9% NaCl (w/v) or approximately 0.154 M

(b) How fertiliser concentrations in agriculture are expressed (NPK ratios, ppm of micronutrients)

(c) The use of molality in studying freezing point depression of radiator coolants in Indian vehicles

(d) Why mole fraction is preferred in distillation calculations for Indian petrochemical industries

Q16. A solution is prepared by dissolving 18 g of glucose (C₆H₁₂O₆) in 178.2 g of water. The density of the resulting solution is 1.05 g/mL.

(a) Calculate the molarity of the solution.

(b) Calculate the molality of the solution.

(c) Calculate the mole fraction of glucose.

[Given: Molar masses: C₆H₁₂O₆ = 180 g/mol, H₂O = 18 g/mol]

Q17. Concentrated sulphuric acid has a density of 1.84 g/mL and is 98% H₂SO₄ by mass.

(a) Calculate the molarity of concentrated H₂SO₄.

(b) Calculate the molality of concentrated H₂SO₄.

(c) How many mL of concentrated H₂SO₄ are needed to prepare 500 mL of 2 M H₂SO₄?

[Given: Molar mass of H₂SO₄ = 98 g/mol]

Q18. An intravenous saline solution used in Indian hospitals contains 0.9 g of NaCl per 100 mL of solution.

(a) Calculate the molarity of this saline solution.

(b) Calculate the molality if the density of the solution is 1.005 g/mL.

(c) A patient receives 1 L of this saline over 8 hours. Calculate the total mass of NaCl administered and the number of moles of Na⁺ ions received.

[Given: Molar mass of NaCl = 58.5 g/mol]