Paper 3B problems

Percentage Purity

I have a sample of sodium chloride which has some limestone powder in it. How would I find out the % of the impurity?HINT:solubility
The sodium chloride is soluble in water but limestone is insoluble so this problem is a "salt" and sand excercise.

  • weigh sample
  • add water to dissolve the sodium chloride
  • filter
  • dry the residue to constant weight

*mass impurity/total mass x 100=%impurity

How could I determine the % of sodium carbonateimpurity in a sample of Sodium chloride?HINT:all sodium salts are soluble

  • weigh sample
  • place in a conical flask connected to a gas syringe

OR measure mass loss on a balance

  • add excess Hydrochloric acid
  • collect gas given off
  • moles carbon dioxide=volume/24000

OR mass carbon dioxide given off/44

  • moles carbon dioxide = moles sodium carbonate
  • RMM sodium carbonate = 106 so mass sodium carbonate = 106 x moles sodium carbonate
  • % impurity= mass sodium caronate/original mass x100

How could I find the % sodium nitrate impurity in a sample of sodium chloride?
HINT:neither salt reacts with acids

  • weigh sample
  • add excess aqueous silver nitrate solution and nitric acid
  • filter off the Silver Chloride ppt, dry to constant weight
  • RMM AgCl = 108 +35.5 = 143.5 so
  • moles AgCl = mass ppt/143.5
  • moles AgCl = moles NaCl so
  • Mass NaCl=moles x 58.5
  • total mass - mass NaCl = mass sodium nitrate
  • mass sodium nitrate/total mass x 100 = %impurity
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