Jahnine M.

asked • 09/15/21

Analysis of a hydrate

Formula of compound used NA2CO3 x H2O

Empty crucible - 12.7825g

Crucible + hydrate 1.0036g

Crucible + content

after 1st heat 13.5546g

after 2nd heat 13.5967g

after 3rd heating 13.5961g


1.What is the mass of hydrate form of compound?

2.What is the mass of anhydrous form ?

3.What is the mass of water driven out?

4.What is the mole of anhydrous form?

5.What is the mole of water?

6.What is the ratio of water : anhydrous form?

7.What is the formula of the hydrate?

Andrew S.

Is this data from experiment or is it given to you as a problem? Could you double check the numbers are correct. Typically, when analyzing a hydrate, the purpose of heating it is to make it anhydrous. In other words, the hydrate has water molecules trapped within it, and heating it releases them, leaving behind only the anhydrous chemical (in this case the Na2CO3). Since water is leaving the hydrate, the mass should decrease after heating, but the data you present has the mass increase after the second heating. If this is experimental, you may want to check that you properly tared the empty crucible and that the scale is clean and balanced. Otherwise, double check the numbers posted. I will discuss a general solution as well.
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09/15/21

Jahnine M.

Yes the data was from an experiment. That why I had to do a 3rd heating.
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09/15/21

1 Expert Answer

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Andrew S. answered • 09/16/21

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In general, when analyzing a hydrate, the goal is to determine how much water is in the material by measuring how much mass is lost after heating. The process of heating a hydrate release the water and makes the material anhydrous. Let's say we have a mass of a hydrate Mh, which after heating is reduced to a mass of Ma. Assume we have heated it adequately long enough for all the water to leave, then the change in mass is the mass of the water in the hydrate, Mw = Mh - Ma. We can determine how many moles of water, nw, left the hydrate by dividing by the molar mass of water, mw -> nw = Mw / mw. We can also determine the number of moles of the chemical by dividing the anhydrous mass (after heating) by the chemical's molar mass, m -> na = Ma / m. Finally, we can determine the molar ratio, x, of water in the hydrate by dividing the number of moles of water by the number of moles of chemical -> x = nw / na.

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