Question

Iwhen performing the experiment for magnesium oxide :

Why is the empty crucible and cover fired to heat?

How critical are the suggested times for heating and cooling?

How can you tell when the magnesium metal has reacted cmpletely?

How cn you tell when the copper wire has reacted compleely?

What are the major sources of experimental error?

Answer 1

(1)There might be some moisture or volatile impurities in the crucible that might alter the mass of the crucible. So, the empty crucible and cover are fired so that the volatile impurities and moisture could be removed.

(2) Crucible should be heated for 5 to 10 minutes in an oven and then it should be cooled in a dessicator till it attain the room temperature. Then we measure its weight and reapet the heating and cooling process till we get the constant mass.

(3) When Mg is burned in presence of oxygen it forms it's oxide and there is an increase in the mass of the crucible due to the formation of the metal oxide. After weighing we agian burned it and check out its weight. if there is an incrase in weight then it means Mg metal has not reacted completely but if there is no increase in the weight then it is an indication of comple reaction means all the Mg has been converted into magnesium oxide.

(4) What we have done for #3 could also be done for #4.

(5)

One of the very common error is an incomplete combustion.

Some of the solid could be lost while transfering it from the crucible.

Some of the metal might react with the moisture and could make it's hydroxide.

Other gases like nitrogen are also available in the air that could react with metal to make its nitride like Mg3N2. So, need to get it react with water to convert Mg3N2 into Mg(OH)2 that could again be converted into MgO on heating.