Common Salts - UNSOLVED PRACTICE SET

Q7. Write the chemical formulae of: (i) Common salt, (ii) Washing soda, (iii) Baking soda, (iv) Bleaching powder, (v) Caustic soda.

Q8. How is bleaching powder prepared? Write the chemical equation. Name two uses of bleaching powder.

Q9. Your mother uses washing soda (Na₂CO₃·10H₂O) while doing laundry. She says it removes dirt and softens water. Explain how washing soda helps in cleaning clothes.

Q10. Why is common salt (NaCl) essential for our body? What health problems can occur due to deficiency or excess of salt in the diet?

Q11. Differentiate between baking soda and washing soda on the basis of: (i) chemical formula, (ii) preparation from common salt, and (iii) two uses of each.

Q12. Write the chemical equation for the reaction of chlorine with dry slaked lime to form bleaching powder. Why must the slaked lime be dry for this reaction?

Q13. Describe the preparation, properties, and uses of the following salts: (i) Common salt (NaCl), (ii) Washing soda (Na₂CO₃·10H₂O), (iii) Baking soda (NaHCO₃), and (iv) Bleaching powder (CaOCl₂). Write the chemical equations for the preparation of washing soda and bleaching powder from common salt.

Q14. A student is given four white crystalline solids: NaCl, NaOH, Na₂CO₃, and NaHCO₃. She has distilled water, dilute HCl, phenolphthalein, and litmus paper. Help her identify each solid by:

(a) Describing the observations when each solid is dissolved in water and tested with litmus paper.

(b) Explaining what happens when dilute HCl is added to each solution.

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

(d) Suggesting a heating test to identify NaHCO₃.

(e) Writing the chemical equation for the reaction of Na₂CO₃ with HCl.

Q15. "Common salt is the starting material for a vast chemical industry that produces essential chemicals for our daily lives." Discuss this statement by explaining: (i) how common salt is used to prepare caustic soda, chlorine, and hydrogen by electrolysis, (ii) how caustic soda is used to make soap and paper, (iii) how chlorine is used to make bleaching powder and PVC, and (iv) the economic importance of the chlor-alkali industry in India.

Q16. A chemical factory produces various products from common salt (NaCl) through the chlor-alkali process:

2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ (electrolysis)

(a) If the factory processes 585 kg of NaCl daily, calculate the mass of NaOH produced. (Molar masses: NaCl = 58.5 g/mol, NaOH = 40 g/mol)

(b) Calculate the volume of chlorine gas produced at STP. (1 mole gas at STP = 22.4 L)

(c) The NaOH produced is used to make soap. If 200 kg of NaOH is used daily, calculate how many 125 g soap bars can be made (assuming soap is 100% NaOH for simplicity).

(d) The chlorine gas is used to make bleaching powder: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. Calculate the mass of bleaching powder produced from the chlorine obtained in part (b). (Molar mass of CaOCl₂ = 143 g/mol)

Q17. A household uses various salts for different purposes:

Table

Salt Amount Used per Month Cost per kg

Common salt (NaCl) 2 kg ₹20

Washing soda (Na₂CO₃·10H₂O) 1 kg ₹35

Baking soda (NaHCO₃) 500 g ₹60

Bleaching powder (CaOCl₂) 250 g ₹80

(a) Calculate the total monthly expenditure on these salts.

(b) If washing soda loses its water of crystallisation and becomes powdery (Na₂CO₃), calculate the percentage loss in mass. (Molar masses: Na₂CO₃·10H₂O = 286 g/mol, Na₂CO₃ = 106 g/mol)

(c) If 1 kg of washing soda effloresces completely, what mass of anhydrous sodium carbonate remains?

(d) Baking soda is heated to make baking powder. Calculate the mass of CO₂ produced when 500 g of NaHCO₃ is heated. (Molar mass of NaHCO₃ = 84 g/mol, CO₂ = 44 g/mol)

(e) Why is bleaching powder stored in airtight containers, and what happens if it is exposed to air for a long time?

Q18. In India, the salt industry is one of the oldest and most important industries. The Sambhar Lake in Rajasthan is a major source of common salt.

(a) Common salt is obtained from seawater or salt lakes by evaporation. Explain this process and why it is a physical change, not a chemical change.

(b) If seawater contains 3.5% NaCl by mass, calculate the mass of salt obtained from 10,000 kg of seawater.

(c) The salt obtained contains impurities like magnesium and calcium salts. How is common salt purified to make it edible?

(d) Iodised salt contains potassium iodate (KIO₃) to prevent iodine deficiency disorders. If 1 kg of salt contains 30 mg of KIO₃, calculate the concentration in ppm (parts per million).

(e) Why is the government of India promoting the use of iodised salt, and what health problems does iodine deficiency cause?