What comprises carbonate and noncarbonate hardness?

Carbonate and noncarbonate hardness in water primarily refer to the hardness caused by different dissolved salts.

Carbonate hardness, also known as temporary hardness, comes from the presence of bicarbonate ions (HCO3-) and carbonate ions (CO32-). This type of hardness can be removed by boiling, which converts bicarbonates into insoluble carbonates that precipitate out of the water. The salts that contribute to carbonate hardness are primarily calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2).

Given this context, the correct answer reflects that the materials causing carbonate hardness are calcium and magnesium bicarbonates.

Noncarbonate hardness, also known as permanent hardness, is typically due to the presence of sulfates, chlorides, or nitrates of calcium and magnesium, which do not precipitate upon boiling. However, they do not contribute to the definition of carbonate hardness.

In summary, the composition of carbonate hardness is accurately represented by the presence of calcium and magnesium bicarbonates, which explains why this answer is correct.