Question

A crucible used in lab to heat solid at high temperature is made of:
A. Sulphur
B. Silicon
C. Graphite
D. Phosphorus

Answer 1

Hint: Crucible is a ceramic in which metals are melted or subjected to very high temperatures. Usually crucibles are made of clay or they can be made from any material which can resist high temperatures or atleast alter its contents.

Complete step by step answer: Graphite is the most commonly used crucible. These crucibles are refractory containers specially designed for heating or melting operations. It is made up of a mixture of clay, graphite, grog (brick used as an additive in clay) and other additives.
In chemical analysis, these are used in quantitative gravimetric analysis (the analysis which is done by measuring mass of an analyte or its derivative). Most common use of crucibles are as follows: Can be used as a precipitate in a chemical analysis method, can be filtered from a few samples or solutions on filter paper. Before heating the crucible and its lid is weighed very accurately on an analytical balance. Then after washing and drying of this filtrate, the leftover residue on the filter paper is placed in the crucible and is heated at very high temperature until all the volatiles and moisture are evaporated out of the sample in the crucible. The special filter paper is completely burned during this process.
Therefore, option C. Graphite is the correct answer.

Additional Information: Porcelain crucibles are hygroscopic in nature, i.e. they absorb moisture from the air which increases their weight. So for this reason, the porcelain crucible is also pre-heated to high temperature before the pre-weighing.

Note: For getting a complete accurate and precise result, the crucible is handled with tongs because sometimes fingerprints can add a little amount of mass to the crucible.