student is given a sample of a sodium carbonate hydrate. He places the sample in

Question

student is given a sample of a sodium carbonate hydrate. He places the sample in a dry, covered crucible and weighs it. The total mass (crucible, cover, and hydrate) is 19.547 grams. The crucible and cover together had previously weighed 17.730 grams. He then heats the crucible to redness for 10 minutes with the cover slightly ajar. After the crucible cools, he weighs the crucible and its contents; the mass is now 18.403 grams, due to the loss of water of hydration. 1. What is the mass of the original sample?

1.what is the mass of the origal sample?

2. What is the mass of the anhydrous residue, i.e., the compound minus the water of hydration?

3. What is the mass of the water that is driven off?

Explanation / Answer

The crucible and cover weights - 17.730 g

The crucible, cover and hydrate is 19.547 g

So the mass of the sodium carbonate hydrate is 19.547g - 17.730g = 1.817 g

1. Mass of the original sample 1.817 g

After heating the crucible with cover and its contents weight 18.403 g

So the mass of the content which is the anhydrous residue is 18.403 g - 17.730 = 0.673 g

2. So the mass of the anhydrous residue is 0.673 g

3. The mass of the water that has been driven off is 1.817g - 0.673 g = 1.144 g

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