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Worksheet: Hard Water


When calcium carbonate (for instance, in limestone) reacts with carbon dioxide and water, a soluble calcium salt is produced. When boiled, this chemical decomposes back to calcium carbonate, forming limescale. What is the name of the calcium salt?

  • A Calcium carboxide
  • B Calcium carbonate
  • C Calcium hydrocarboxide
  • D Calcium hydrogen carbonate
  • E Calcium hydrocarbon dioxide


When water is boiled, some of the calcium salts can decompose and precipitate, decreasing the hardness of the water. Other salts do not decompose upon heating, causing permanent hardness. Which of the following salts would cause permanent hardness?

  • A Calcium hydrogen carbonate
  • B Calcium carbonate
  • C Calcium sulfite
  • D Calcium sulfate
  • ECalcium oxide


Which of the following is the most common unit for measuring water hardness?

  • A mol/kg
  • B g/cm3
  • C kg/L
  • D mg/L
  • E kg/kg