Question

Analysis of a river water sample showed the presence of the following ions Ca²⁺, Na⁺, Cl⁻ , NO³⁻.

1. Name the type of water hardness present in the sample. 
2. Describe one precipitation method that can be used to soften the water. 
3. The water sample was passed through a resin as shown in the figure .
            
   • Write an equation for a reaction that took place in the column. 
   • Complete treatment of the water sample required passing it through another resin. Give the formula of this resin. 
   • Explain why a river water sample that has been treated using resins may still require boiling to make it safe for drinking. 

Answer 1

1. Permanent
2.   
   • Addition of washing soda/NaCO₃✓1
   • Ca²⁺and Mg²⁺ precipitates as carbonates which can be filtered off✓
3.   
   •  Resin
     RNH₃⁺OH⁻(s) + NO₃⁻(aq) or Cl⁻→ RNH₃⁺NO⁻(s)(Cl⁻if its over used) + OH(aq)
   • RSO₃⁻H⁺   OR RCOO⁻H⁺   
   •   
     • Resin does not kill bacteria/pathogen
     • Boiling kills