Question 1

a. A water sample contains the following impurities:
Mg(HCO₃)₂ = 73 mg/L (formula weight 146 amu)
MgCl₂ = 180 mg/L (formula weight 95 amu)
CaSO₄ = 68 mg/L (formula weight 136 amu)
Ca(NO₃)₂ = 164 mg/L (formula weight 164 amu)
NaCl = 5.85 mg/L (formula weight 58.5 amu)
(i) If the given water sample has been treated with lime and soda, provide the relevant chemical reactions associated with the impurities. (Explanations are not required.)
(ii) Calculate the amount of lime and soda required (in kg) to remove the above-mentioned impurities from 5 × 10⁶ litres of water. (Assume the purity of lime and soda is 100%.) (2+3 marks)

b. A sample of water upon analysis gave the following data: MgCl₂ = 380 mg/L, MgSO₄ = 480 mg/L, CaSO₄ = 544 mg/L and Ca(HCO₃)₂ = 486 mg/L. Calculate the total hardness in ppm. (2 marks)

c. What is hardness of water? Mention various units used for its expression and show their relation also. Why is 'CaCO₃ equivalents' used to represent hardness? (3 marks)