Bases - Properties and Examples - UNSOLVED PRACTICE SET

Q7. Define a base. Classify bases into strong bases and weak bases, giving two examples of each.

Q8. Write the chemical formulae of the following bases: (i) Sodium hydroxide, (ii) Potassium hydroxide, (iii) Calcium hydroxide, (iv) Ammonium hydroxide.

Q9. Your mother uses soap to wash clothes and notices that soap feels slippery and tastes bitter if it accidentally gets into her mouth. Explain these properties of soap in terms of its chemical nature.

Q10. Why are strong bases like sodium hydroxide called "caustic"? What precautions should be taken while handling them in the laboratory?

Q11. Distinguish between an alkali and a base. Are all bases alkalis? Are all alkalis bases? Explain with examples.

Q12. Write the ionisation equations for: (i) Sodium hydroxide in water, and (ii) Calcium hydroxide in water. What do these equations tell you about the nature of these bases?

Q13. Define bases and describe their general properties. Explain the difference between strong bases and weak bases with examples. What are alkalis? Why are all alkalis bases but not all bases are alkalis? Write the ionisation equation of sodium hydroxide in water.

Q14. A student is given four unlabelled bottles containing: sodium hydroxide solution, calcium hydroxide solution (limewater), ammonium hydroxide solution, and distilled water. She has red litmus paper, phenolphthalein, and aluminium metal. Help her identify the bases by:

(a) Explaining what happens when each solution is tested with red litmus paper.

(b) Describing the colour change with phenolphthalein for each solution.

(c) Explaining how aluminium can help distinguish between strong and weak bases.

(d) Suggesting one additional test to identify calcium hydroxide specifically.

Q15. "Bases play a crucial role in our daily lives, from cleaning our homes to treating medical conditions." Discuss this statement by explaining: (i) the use of bases in soaps and detergents, (ii) the role of antacids in treating acidity, (iii) the use of lime (calcium hydroxide) in agriculture and construction, and (iv) the importance of bases in the chemical industry.

Q16. A chemistry laboratory prepares standard solutions of bases for titration experiments:

(a) 4 g of NaOH is dissolved in water to make 250 mL of solution. Calculate the molarity. (Molar mass of NaOH = 40 g/mol)

(b) If 20 mL of this NaOH solution is diluted to 200 mL, what is the new molarity?

(c) Slaked lime (Ca(OH)₂) is used to neutralize acidic soil. If a farmer uses 7.4 g of Ca(OH)₂, calculate the number of moles. (Molar mass of Ca(OH)₂ = 74 g/mol)

(d) If this amount of Ca(OH)₂ is dissolved in 500 mL of water, calculate the molarity of the resulting limewater.

Q17. In a school laboratory, students test various household substances to identify bases:

Table

Substance Test with Red Litmus Test with Phenolphthalein Feel to Touch

A Turns blue Pink Slippery

B No change Colourless Normal

C Turns blue Pink Slippery

D No change Colourless Normal

(a) Identify which substances are basic and which are neutral.

(b) Substances A and C both turn phenolphthalein pink. How can you distinguish between a strong base (like NaOH) and a weak base (like NH₄OH) using pH paper?

(c) If substance A is NaOH solution with pH = 13, calculate the [OH⁻] concentration.

(d) If substance C is NH₄OH solution with pH = 11, calculate the [OH⁻] concentration.

(e) Why do both strong and weak bases feel slippery to touch?

Q18. A soap manufacturing company in India produces bathing soap and washing soap.

(a) Soaps are sodium or potassium salts of fatty acids. Explain why soap solutions are basic in nature.

(b) If a soap solution has a pH of 9, calculate the [H⁺] and [OH⁻] concentrations.

(c) The company tests its soap by dissolving 10 g in 100 mL water. If the resulting solution has [OH⁻] = 10⁻⁵ M, calculate the pH.

(d) Washing soap is more basic (higher pH) than bathing soap. Why is this difference important for their respective uses?

(e) If a bathing soap has pH 8 and a washing soap has pH 10, calculate the ratio of their [H⁺] concentrations. What does this tell you about the difference in alkalinity?