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17 December, 14:53

A hydrate is a compound that has water molecules within its crystal structure. Magnesium sulfate heptahydrate, MgSO4·7H2O, is a hydrated form of magnesium sulfate. The hydrated compound has 7 moles of H2O for each mole of MgSO4. When 5.06 grams of MgSO4·7H2O are heated to at least 300. oC in a crucible by using a laboratory burner, the water molecules are released. The sample was heated repeatedly, until the remaining MgSO4 had a constant mass of 2.47 grams. During this laboratory activity, appropriate safety equipment was used and safety procedures were followed. Explain why the sample in the crucible was heated repeatedly until the sample had a constant mass.

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  1. 17 December, 15:52
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    We are heating the sample repeatedly to become a pure compound of only MgSO4 (withot H2O) and a constant mass.

    Explanation:

    Step 1: Data given

    Mass of MgSO4·7H2O = 5.06 grams

    The remaining MgSO4 had a constant mass of 2.47 grams.

    Step 2: Explain why the sample in the crucible was heated repeatedly until the sample had a constant mass.

    Before heating the compound has magnesium sulfate and water.

    The total mass of this compound is 5.06 grams

    By heating we try to eliminate the water.

    After heating there remain mgSO4 with a mass of 2.47 grams

    This means 5.06 - 2.47 = 2.59 grams is water. All of this is eliminated.

    The heating process happens repeatedly to make sure the final compound is pure. So the 2.47 grams os only MgSO4. If the mass would not be constant. It means the compound is not pure, the not all the water is eliminated yet.

    So we are heating the sample repeatedly to become a pure compound of only MgSO4 (withot H2O) and a constant mass.
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