Neutralisation Reaction - UNSOLVED PRACTICE SET

Q7. Define neutralisation reaction. Write the general equation for the neutralisation of an acid with a base.

Q8. Write balanced chemical equations for the neutralisation of: (i) Hydrochloric acid with sodium hydroxide, (ii) Sulphuric acid with potassium hydroxide, (iii) Nitric acid with calcium hydroxide.

Q9. Your younger brother suffers from acidity after eating too many samosas. Your mother gives him a spoon of baking soda dissolved in water. Explain the neutralisation reaction that occurs in his stomach and why he feels better.

Q10. Why is the reaction between a strong acid and a strong base called an exothermic reaction? What happens to the temperature of the solution during neutralisation?

Q11. What is the role of an indicator in a neutralisation reaction? Why can't we simply mix an acid and a base without an indicator when we want to obtain a neutral solution?

Q12. A farmer finds that his soil is too acidic for growing wheat. He adds slaked lime (calcium hydroxide) to the soil. Write the neutralisation reaction that occurs and explain why this helps the crops.

Q13. Define neutralisation reaction with examples. Explain why neutralisation reactions are exothermic. Describe an experiment to demonstrate the neutralisation of hydrochloric acid with sodium hydroxide using an indicator. How does this reaction help in: (i) treating acidity, (ii) treating alkaline soil, and (iii) treating bee stings and wasp stings?

Q14. A student performs a titration experiment to neutralise 25 mL of dilute HCl with NaOH solution. She uses phenolphthalein as an indicator.

(a) Describe the colour change she observes at the end point.

(b) If 20 mL of 0.1 M NaOH is required to neutralise the acid, calculate the molarity of the HCl solution.

(c) Write the balanced chemical equation for the reaction.

(d) Calculate the number of moles of HCl present in the 25 mL sample.

(e) Why is phenolphthalein preferred over litmus for this titration?

Q15. "Neutralisation reactions are nature's way of restoring balance — in our bodies, in our soil, and in our environment." Discuss this statement by explaining: (i) how antacids work to neutralise stomach acid, (ii) how farmers use neutralisation to treat acidic or alkaline soil, (iii) how neutralisation is used in wastewater treatment, and (iv) the role of neutralisation in treating insect bites and stings.

Q16. A chemistry laboratory prepares solutions for neutralisation experiments:

(a) 20 mL of 0.5 M HCl is neutralised by NaOH solution. Calculate the volume of 0.5 M NaOH required.

(b) If the neutralisation is performed using Ca(OH)₂ instead of NaOH, what volume of 0.25 M Ca(OH)₂ is needed to neutralise the same amount of HCl?

(c) The heat evolved during this neutralisation is 57.3 kJ per mole of water formed. Calculate the total heat evolved when 20 mL of 0.5 M HCl is completely neutralised.

(d) If this heat is used to raise the temperature of 50 g of water, calculate the temperature rise. (Specific heat capacity of water = 4.2 J/g°C)

Q17. An antacid tablet contains sodium bicarbonate (NaHCO₃) as the active ingredient.

(a) Write the neutralisation reaction between NaHCO₃ and stomach acid (HCl).

(b) If one tablet contains 840 mg of NaHCO₃, calculate the mass of HCl it can neutralise. (Molar masses: NaHCO₃ = 84 g/mol, HCl = 36.5 g/mol)

(c) If the stomach contains 100 mL of gastric juice with pH 1 (approximately 0.1 M HCl), how many tablets are needed to completely neutralise the acid?

(d) Why do doctors sometimes recommend antacids containing magnesium hydroxide instead of sodium bicarbonate?

(e) Calculate the volume of CO₂ gas produced at STP when one tablet reacts with excess HCl. (1 mole gas at STP = 22.4 L)

Q18. A farmer in Punjab has acidic soil with pH 5.5. He wants to grow wheat, which requires soil pH between 6.5 and 7.5.

(a) Write the neutralisation reaction when slaked lime (Ca(OH)₂) is added to acidic soil containing H⁺ ions.

(b) If the farmer needs to treat 1 hectare (10,000 m²) of soil to a depth of 20 cm, and the soil density is 1.3 g/cm³, calculate the total mass of soil.

(c) If the soil requires 2 tonnes of Ca(OH)₂ per hectare to raise the pH to 7, calculate the number of moles of Ca(OH)₂ needed. (Molar mass of Ca(OH)₂ = 74 g/mol)

(d) How many moles of H⁺ ions can this amount of Ca(OH)₂ neutralise?

(e) Why is it important for Indian farmers to test soil pH before planting crops? Give two examples of crops that grow well in specific pH ranges.