Lesson Worksheet: Water Hardness Chemistry

In this worksheet, we will practice describing the composition and properties of hard water and explaining how water hardness can be measured and avoided.


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?

  • ACalcium hydrocarbon dioxide
  • BCalcium hydrocarboxide
  • CCalcium hydrogen carbonate
  • DCalcium carbonate
  • ECalcium carboxide


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?

  • ACalcium carbonate
  • BCalcium oxide
  • CCalcium sulfate
  • DCalcium hydrogen carbonate
  • ECalcium sulfite


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

  • Akg/L
  • Bmg/L
  • Ckg/kg
  • Dg/cm3
  • Emol/kg


Which of the following is the correct definition of water hardness?

  • AThe amount of sodium chloride dissolved in the water
  • BThe amount of dissolved solids in the water
  • CThe amount of dissolved salts in the water
  • DThe amount of calcium and magnesium ions in the water
  • EThe amount of soap that will not lather when using the water

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