A chemical experiment group for the determination of the composition of gypsum (CaSO4?xH2O), that is, to measure the value of x, did the following experiments, will contain water of crystallization of calcium sulfate in the crucible (1) solution: gypsum heated decomposition of the mass is the mass of water, by the experimental data know 3.44g?CaSO4?xH2O completely decomposed to get anhydrous CaSO42.72g, then:

CaSO4?xH2O═CaSO4+xH2O

13618x

2.720.72

that is 136:2.72=18x:0.72? Solve x=2 So the chemical formula of gypsum is CaSO4?2H2O.

(2) From the experimental data, we know that the mass of gypsum in the A-B section is 2.90g, of which CaSO42.72g, H2O0.18g. At this time, the chemical formula can be expressed as 2CaSO4?H2O. is:

(1) CaSO4?2H2O;

(2) The reason is that the mass of gypsum is 2.90g, according to the data in the figure can be seen in the end the solid mass is unchanged, which means that there is no more water of crystallization, that is, the mass of CaSO4 is 2.72g, so the mass of H2O is 2.90g-2.72g ═0.18g. Then the ratio of the mass of calcium sulphate to water is: 272:18, because the relative molecular mass ratio of calcium sulfate to water is 136:18, so calcium sulfate should be put in front of the 2, so at this time its chemical formula can be expressed as 2CaSO4?H2O. The substance is chemically stable, not easy to decompose by heat.