Question

If you do not heat your crucible strongly enough to remove all volatile impurities when you heat the crucible empty, what will be the result if those impurities are completely volatilized when heating your sample?a) your sample will weigh more than it is supposed to after heating , causing the mass of water to be less than it is supposed to be b) your sample will weigh less than it is supposed to after heating, causing the mass of water to be higher than it is supposed to be c) the loss of water happening during the initial heating or during the second heating isn't relevant

Answer 1

We have a crucible and we don't heat it enough to remove all the volatile impurities. For example:

mass of crucible empty = 100 g

mass of impurities = 1 g

mass of crucible + impurities = 101 g

The real mass of the crucible is 100 g but we didn't remove all the impurities so when we weigh it we get a reading of 101 g.

We add a sample of a salt that weighs 20 g. We heat it and after that we measure the crucible and the sample weighs 115 g.

mass of sample before heating = 20 g

mass of sample + crucible after heating = 115 g

We can say that 5 g of water were vaporized but we had 1 g of impurities that also vaporized so actually they were 4 g.

So the answer is: b) your sample will weigh less than it is supposed to after heating, causing the mass of water to be higher than it is supposed to be