Explain why iron sulphide is a compound and not just a mixture of the two elements iron and sulphur.
Explain why iron sulphide has different properties to a mixture of iron and sulphur and also describe and explain tests that can distinguish between iron sulphide and a mixture of iron and sulphur.
Iron and sulfur are both elements from the periodic table of elements. As such, each one has its own unique set of physical and chemical properties. Iron is a metal, while sulfur is a nonmetal. When these two are heated together, the iron atoms combine with the sulfur atoms to make a compound known as iron sulphide. A compound is different from elements in that it is made from the chemical union of two or more elements. Iron sulphide is not iron or sulfur; it is a pure substance with its own set of distinguishing physical and chemical characteristics. A mixture, on the other hand, is what you get by combining two or more elements, but not chemically combining them. In the case of the iron and the sulfur, if you mix them and provide no heat, you simply have a mixture of iron and sulfur. Mixtures are different from compounds in that they are easily separated. A magnet could be used to separate the iron from the sulfur, because iron is attracted to magnets, while sulfur is not.
"What is the difference between iron and sulfur, and iron sulfide? Sulfur and iron: since this is a mixture, the sulfur retains its properties (its yellow color, for example), and the iron retains its properties (its black color, for example). These properties can be used to separate the two elements.
"For iron sulfide, two elements (sulfur and iron) are heated together so that they form the compound iron sulfide. Although iron sulfide contains both sulfur and iron, it is not a mixture: it is a pure substance. Both the sulfur and the iron have 'given up' their individual properties to become a compound. This, then, is a pure substance.
"How could you go about getting the iron and sulfur out of iron sulfide? You would have to decompose the iron sulfide back into a mixture of iron and sulfur and then separate the two."
(see "Module 4 Chemistry Review Notes") --