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The topic of hydrates in chemistry is an interesting one.
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What a hydrate is is an ionic compound that as it is formed has water that remains loosely bonded to its crystal structure.
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When we indicate a hydrated form of an ionic compound by using a dot in its chemical formula, and what comes after the dot indicates the relative amount of water, in this case five moles for every one mole of the ionic compound itself so we have copper sulfate pentahydrate this substance which is blue in color appears to be completely dry but has water within its matrix that means that an appreciable amount of its mass is water you can do an experiment to figure out how much water is in a hydrate by first weighing out some of the hydrated form of the substance, adding it to some kind of container to heat it with, perhaps a crucible with a lid, then heating it up.
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Now when you do this, you want to be careful to heat it gently at first because this will actually spatter at the bottom of the container and we don't want that spatter to fly away.
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We do need to have a bit of of an opening so that as you heat this up the water that is driven off has a way to escape.
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We don't want it to stay within the container.
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So heat gently at first and then do it a little stronger but not too strong.
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Often if the bottom of the container gets really hot and is red, that will actually encourage the crystals to turn brown because it will start to react with oxygen in the air.
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We want to avoid that.
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After you've conducted the experiment and all the water leaves, you want to allow it to cool with the lid back on.
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Because at that point, we don't want any of that water that's outside to make its way back in and rehydrate our sample.
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Mathematically, we know that the total mass, what you had in the beginning, the hydrated sample, has to be equal to the residue that's left over after you've heated.
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It and the water that is now left.
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So by measuring the original amount of mass when the copper sulfate is blue and then measuring the mass after you've dehydrated it and it's now an off -white color, we can determine how much water has been lost.
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And from that we can figure out the chemical formula.
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To do that, we need to do some mole conversions.
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So let's do an example where perhaps we started with a total mass originally of 1 .30 grams.
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And we do an experiment.
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This particular experiment we know is with a different substance hydrated magnesium sulfate.
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So we had 1 .3 .0 in the beginning, which is the hydrated version.
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We heated up like i described above.
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And we have 0 .635 grams remaining.
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We know that the water, the mass that's lost, has to be the water.
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So if we subtract, we know we have 0 .6 .65 grams of water.
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So we can determine now a few different characteristics of this, right? if we wanted a percentage basis, like how much of that mass, was a percent water.
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All we'd have to do is take 0 .665 grams, which is the water.
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Divide that by the total mass, and that would give us a percent of about, of course, multiply it by 100, about 51 .2 percent water.
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Now that's kind of interesting, but we might also want to know the formulas.
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And to do formulas, formulas require moles or particles, individual atoms, not mass.
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So we have to do some mole conversions.
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So let's do that for both the water and the magnesium sulfate.
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So these are best done through something we often call dimensional analysis, but really they're just ratios...