I hope someone can help me understand this experiment. Law of Definite Proportio

Question

I hope someone can help me understand this experiment. Law of Definite Proportions

Calculate and record the following for the experiment performed with 20 g KClO3

a. mass of the crucible with manganese(IV) dioxide (in grams) 88.1g

b. mass of the crucible after potassium chlorate has been added (in grams) 108.100g

c. mass of the crucible after heating (in grams) 100.267

d. mass of potassium chloride (in grams) 12.167g

e. mass of oxygen in sample of potassium chlorate (in grams) 7.833g

f. mass percent of oxygen in potassium chlorate .64379 or 64.38% (not sure if this is right)

Then we had to calculate the theoretical mass and I got 39.166%

Next we have to calculate the percent error in the experiment using the experimental and theoretical values of the mass percent of oxygen. So that is [(experimental value)-(theoretical value)]/theoretical value*100% but not sure if this is right .39166-.64379/64.38=.003916. Please help.

Explanation / Answer

Well, the procedure is fine, but you got wrong in some results.

For start, the mass of oxygen in the sample is correct, but the percent is wrong because you took the mass of potassium chloride (KCl) and there's no oxygen in there. You have to take the mass of KClO3 which is 20 g so:

7.833 / 20 * 100 = 39.17%

Now, the theorical mass would be the theorical mass of Oxygen you'll obtain in the reaction, this is another value. And the relative error, it is calculated like you did, but you need to correct the value of oxygen in the sample. Check that value again and get back here with the info.

Hope this helps

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