Lime softening reduces hardness by precipitation of calcium and magnesium as carbonates and hydroxides.

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Prepare for the ADEQ Water Treatment Grade 4 Test. Study with flashcards and multiple-choice questions, with each question offering hints and explanations. Ace your exam!

Multiple Choice

Lime softening reduces hardness by precipitation of calcium and magnesium as carbonates and hydroxides.

Explanation:
Lime softening works by removing the ions that cause hardness: calcium and magnesium. When lime (Ca(OH)2) is added, the water’s pH rises and carbonate species form. Calcium and magnesium then react with carbonate and hydroxide to become insoluble precipitates—calcium carbonate and magnesium hydroxide—that settle out of the water. Removing these ions from solution directly reduces water hardness. The other substances don’t capture the main mechanism of lime softening for hardness. Iron and manganese can be removed by oxidation and filtration, but that’s a different pathway. Sodium, potassium, and aluminum aren’t the primary hardness-causing ions targeted by this process.

Lime softening works by removing the ions that cause hardness: calcium and magnesium. When lime (Ca(OH)2) is added, the water’s pH rises and carbonate species form. Calcium and magnesium then react with carbonate and hydroxide to become insoluble precipitates—calcium carbonate and magnesium hydroxide—that settle out of the water. Removing these ions from solution directly reduces water hardness.

The other substances don’t capture the main mechanism of lime softening for hardness. Iron and manganese can be removed by oxidation and filtration, but that’s a different pathway. Sodium, potassium, and aluminum aren’t the primary hardness-causing ions targeted by this process.

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