Concentration Terms Molarity Molality Normality Mole Fraction - UNSOLVED PRACTICE SET

Q7. Define molarity and molality. Write their units and formulas.

Q8. What is normality? How is it related to molarity for acids and bases?

Q9. Calculate the molarity of a solution containing 5.85 g of NaCl in 500 mL of solution.

Q10. Why does molarity change with temperature while molality does not?.

Q11. Your mother prepares lemonade by mixing 50 g of sugar in 1 L of water. Your father prepares his chai by mixing 20 g of tea leaves in 500 mL of water. Who has made a more concentrated solution? How would you express the concentration of each solution in terms of mass/volume percent?

Q12. What is the n-factor? Calculate the n-factor for:

(a) HCl in acid-base reactions

(b) H₂SO₄ in acid-base reactions

(c) NaOH in acid-base reactions

Q13. Define and compare the four concentration terms: molarity, molality, normality, and mole fraction. For a solution prepared by dissolving 10 g of NaOH in 250 g of water (density of solution = 1.1 g/mL), calculate:

(a) Molarity

(b) Molality

(c) Normality

(d) Mole fraction of NaOH

(Atomic masses: Na = 23 u, O = 16 u, H = 1 u)

Q14. Explain the relationship between molarity and molality. Derive the formula connecting them. For an aqueous solution of sulphuric acid with molarity 18 M and density 1.8 g/mL, calculate:

(a) The molality of the solution

(b) The mass percent of H₂SO₄

(c) The mole fraction of H₂SO₄

(Atomic masses: H = 1 u, S = 32 u, O = 16 u)

Q15. A chemistry teacher prepares three solutions for a demonstration:

Solution A: 0.1 M HCl

Solution B: 0.1 N H₂SO₄

Solution C: 0.1 m NaOH

(a) Calculate the volume of Solution A needed to neutralize 25 mL of Solution C.

(b) Calculate the volume of Solution B needed to neutralize 25 mL of Solution C.

(c) Why are the volumes different in (a) and (b) even though all solutions are 0.1 in concentration?

(d) If the teacher wants to prepare 500 mL of 0.1 M HCl from concentrated HCl (12 M, density 1.18 g/mL), what volume of concentrated acid should she use?

(Atomic masses: H = 1 u, Cl = 35.5 u, Na = 23 u, O = 16 u, S = 32 u)

Q16. Calculate:

(a) The molarity of a solution prepared by dissolving 4 g of NaOH in 250 mL of solution.

(b) The molality of a solution containing 171 g of sugar (C₁₂H₂₂O₁₁) in 500 g of water.

(c) The mole fraction of ethanol in a solution prepared by mixing 46 g of ethanol with 72 g of water.

(Atomic masses: Na = 23 u, O = 16 u, H = 1 u, C = 12 u, S = 32 u)

Q17. A commercial sulphuric acid solution has a density of 1.84 g/mL and contains 98% H₂SO₄ by mass.

(a) Calculate the molarity of this solution.

(b) Calculate the molality of this solution.

(c) Calculate the normality of this solution.

(d) How much water should be added to 100 mL of this acid to make it 1 M?

(Atomic masses: H = 1 u, S = 32 u, O = 16 u)

Q18. A pharmaceutical company needs to prepare 500 mL of 0.9% saline solution (NaCl in water) for medical use. The solution has a density of 1.005 g/mL.

(a) Calculate the mass of NaCl required.

(b) Calculate the molarity of the saline solution.

(c) Calculate the molality of the saline solution.

(d) If a patient needs 1 litre of this solution per day through IV, how many moles of NaCl does the patient receive daily?

(Atomic masses: Na = 23 u, Cl = 35.5 u, O = 16 u, H = 1 u)