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When calcium carbonate ⁠— for instance, in limestone ⁠— reacts with carbon dioxide and water, a soluble calcium salt is produced.

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When boiled, the chemical decomposes back to calcium carbonate, forming limescale.

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What is the name of the calcium salt?

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Calcium carbonate has the formula CaCO₃.

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Calcium, in group two, forms ions with a two plus charge, while the carbonate anion has a charge of two minus.

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So these combine together to form a neutral compound, CaCO₃.

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Calcium carbonate reacts with carbon dioxide, CO₂, and water, H₂O, forming an as-yet-unknown soluble calcium salt.

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If an aqueous solution of this salt is boiled, like it might be in a kettle, calcium carbonate is regenerated.

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What the question is asking for is the name of the calcium salt.

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When treated with carbon dioxide and water, calcium carbonate will form calcium hydrogen carbonate.

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HCO₃− is the formula of the hydrogen carbonate anion.

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It takes two of the hydrogen carbonate anion to counterbalance the two plus charge of the calcium ion.

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So the name of the salt produced when carbon dioxide and water react with calcium carbonate is calcium hydrogen carbonate.

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An interesting demonstration of this reaction occurs with limewater.

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When carbon dioxide is bubbled through limewater, a solution of calcium hydroxide, a cloudy suspension of calcium carbonate forms, turning the liquid cloudy.

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This is why limewater is used as a confirmatory test for the presence of carbon dioxide.

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However, if the flow of carbon dioxide is continued into the suspension of calcium carbonate, the solution will go clear again because soluble calcium hydrogen carbonate is formed.

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This reaction is quite slow though.

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So back to our question, the name of the calcium salt formed when calcium carbonate reacts with carbon dioxide and water is calcium hydrogen carbonate.