Which ions shall be removed to make hard water soft?
Correct answer: B. Ca2+ and Mg2+
- A. Ca+2 and SO42-
- B. Ca2+ and Mg2+
- C. SO42- and Cl-
- D. HCO3- and SO42-
Explanation
Hard water contains an excess of Ca2+ and/or Mg2+ ions, which form insoluble salts with soap, causing scum to form. To make hard water soft, the Ca2+ and Mg2+ ions must be removed. This can be done through ion exchange or by adding a chemical such as sodium carbonate, which reacts with the Ca2+ and Mg2+ ions to form insoluble precipitates that can be filtered out.
This question appeared on the NUMS 2019 (cancelled sitting) paper, which you can sit online with every answer explained.
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About Reactions of Group II Elements
Group II reactions cover the behaviour of beryllium, magnesium, calcium, strontium and barium with water, oxygen, halogens, acids and nitrogen. The trends in reactivity, hydroxide solubility and basicity, along with the thermal decomposition of carbonates and nitrates, depend on increasing atomic size down the group.
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