Preparation and Uses of Important Salts - UNSOLVED PRACTICE SET

Q7. How is Plaster of Paris prepared? Write the chemical equation. Why is it called Plaster of Paris?

Q8. Write the chemical formula of Plaster of Paris. What happens when it is mixed with water? Give two uses of Plaster of Paris.

Q9. Your younger sibling broke his arm and the doctor put a white cast on it. After a few weeks, the cast became hard like stone. Explain the chemical changes involved in the setting of Plaster of Paris.

Q10. How is washing soda prepared from sodium chloride? Write the chemical equations involved in the process.

Q11. What is efflorescence? Give an example of a salt that shows efflorescence. What happens to the salt during efflorescence?

Q12. Differentiate between gypsum and Plaster of Paris on the basis of: (i) chemical formula, (ii) water content, and (iii) uses.

Q13. Describe the preparation of Plaster of Paris from gypsum with a chemical equation. Explain what happens when Plaster of Paris is mixed with water and why it sets hard. List at least four uses of Plaster of Paris in medicine, construction, and art.

Q14. A student is learning about the preparation of important salts in the laboratory:

(a) Describe how washing soda (Na₂CO₃·10H₂O) is prepared from sodium chloride. Write all the chemical equations involved.

(b) Describe how bleaching powder (CaOCl₂) is prepared from slaked lime and chlorine. Write the chemical equation.

(c) Explain why Plaster of Paris must be stored in airtight containers.

(d) What is the difference between the preparation of baking soda and washing soda from sodium chloride?

(e) Why is the Solvay process important for the industrial preparation of washing soda?

Q15. "The preparation and uses of salts have transformed human civilization — from ancient medicine to modern construction." Discuss this statement by explaining: (i) the historical importance of common salt in trade and food preservation, (ii) the role of Plaster of Paris in modern medicine and dentistry, (iii) the use of bleaching powder in water purification and sanitation, and (iv) the importance of washing soda in the Indian textile and glass industries.

Q16. A hospital uses Plaster of Paris (CaSO₄·½H₂O) for making casts for fractured bones.

(a) If a cast requires 200 g of Plaster of Paris, calculate the mass of gypsum (CaSO₄·2H₂O) needed to prepare it. (Molar masses: CaSO₄·2H₂O = 172 g/mol, CaSO₄·½H₂O = 145 g/mol)

(b) When Plaster of Paris sets, it converts back to gypsum. Write the chemical equation and calculate the mass of water absorbed when 200 g of Plaster of Paris sets.

(c) If the hospital treats 50 fracture patients per month and each cast requires 200 g of Plaster of Paris, calculate the monthly requirement.

(d) Why does the setting of Plaster of Paris produce a slight temperature rise? What type of reaction is this?

Q17. A glass manufacturing unit in India uses washing soda (Na₂CO₃) as one of the raw materials.

(a) The glass-making reaction is: Na₂CO₃ + CaCO₃ + 6SiO₂ → Na₂O·CaO·6SiO₂ + 2CO₂. If the factory uses 530 kg of Na₂CO₃ daily, calculate the mass of glass produced. (Molar masses: Na₂CO₃ = 106 g/mol, glass = 478 g/mol)

(b) Calculate the volume of CO₂ released at STP during this process.

(c) Washing soda is prepared by the Solvay process. If the factory produces its own washing soda from NaCl, calculate the mass of NaCl needed to produce 530 kg of Na₂CO₃. (Molar mass of NaCl = 58.5 g/mol)

(d) Why is the glass industry important for India's economy? Name two major glass manufacturing regions in India.

Q18. A water treatment plant in a city in India uses bleaching powder to disinfect drinking water.

(a) When bleaching powder is added to water, it releases chlorine: CaOCl₂ + H₂O → Ca(OH)₂ + Cl₂. If 14.3 g of bleaching powder is used, calculate the mass of chlorine released. (Molar masses: CaOCl₂ = 143 g/mol, Cl₂ = 71 g/mol)

(b) The chlorine then reacts with water: Cl₂ + H₂O → HCl + HOCl. The HOCl kills bacteria. If 0.71 g of Cl₂ is released, calculate the mass of HOCl formed. (Molar mass of HOCl = 52.5 g/mol)

(c) The WHO recommends 0.2–0.5 mg/L of free chlorine in drinking water. If a treatment plant processes 5 million litres of water per day, calculate the minimum and maximum mass of chlorine needed daily.

(d) Why is bleaching powder preferred over liquid chlorine for water treatment in rural areas of India?

(e) Calculate the cost of bleaching powder needed for one month (30 days) if the plant uses the minimum recommended chlorine level and bleaching powder costs ₹80 per kg.