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Hi there.
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In this question, we are trying to calculate the mass percent of calcium in this compound.
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So the first thing we need is a chemical formula.
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So we are putting calcium together with phosphorus.
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And calcium is in group two of the periodic table.
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So when it makes ions, it will make ions with a two plus charge.
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Phosphorus is in group five of the periodic table.
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So it makes ions with a three negative charge.
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We know that to write a formula correctly, the charges have to add to zero.
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So the easiest way to determine the charge of this compound is to crisscross the charges.
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In other words, there's a two on calcium.
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So the two becomes a subscript on phosphorus.
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And there's a three.
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We're ignoring the negative sign here.
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There's a three on the phosphorus.
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So that means three calciums.
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Because look what that gives us.
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3 times 2 positive is 6 positive, and 2 times 3 negative is 6 negative...