Knowing molecular formulas

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Knowing molecular formulas

Postby NatalieSDis1A » Sun Apr 08, 2018 10:52 am

For question E.9 in the homework it asks for the formula of magnesium sulfate heptahydrate. However, the question does not provide information (such as number of moles of each element used or percent composition) to find the molecular formula. Should I know from the chemical name what the molecular formula looks like? If so, is that something that has to be memorized?

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Re: Knowing molecular formulas

Postby Chem_Mod » Sun Apr 08, 2018 11:23 am

From the name, the formula can be obtained. The formula is . Sulfate is SO42-, so to get the ion charges to cancel with Mg2+, you need 1:1, thus MgSO4. This compound is hydrated, by 7 or "hepta", so you need 7H2O afterwards. This is explained in earlier parts of fundamentals section if you need to review it and is something that is expected to have been retained from high school chemistry.

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