Chemistry

Matter in Our Surroundings

To Study the Properties of a Mixture of Iron and Sulphur

When iron filings (or iron powder) and sulphur powder are mixed tog is obtained. Let us study the properties of this mixture.
1. If we put a magnet in the mixture of iron filings and sulphur, the iron particles are attracted by the magnet, they stick to the magnet and get separated from sulphur (see Figure 19). Sulphur is not attracted by the magnet, so it is left behind. Thus, a mixture of iron filings and sulphur has been separated into its constituents, iron and sulphur, by the physical method of using a magnet.
Alternatively, if we shake the mixture of iron filings and sulphur with an organic liquid known as carbon disulphide (

CS

₂), then sulphur dissolves in it but iron does not dissolve. On filtration, iron is obtained as a residue and sulphur is recovered from the filtrate by evaporating carbon disulphide.Thus, a mixture of iron filings and sulphur has been separated by another physical method of using carbon disulphide solvent (followed by filtration and evaporation). From these two experiments we conclude that a mixture can be separated into its constituents by physical processes (like filtration, evaporation, sublimation, distillation, solvents, magnet,etc.).
2.If dilute sulphuric acid is added to the mixture of iron filings and sulphur, the iron part reacts with sulphuric acid and hydrogen gas is produced (which is a colourless and odourless gas). Sulphur remains unchanged. This shows that a mixture of iron and sulphur shows the properties of iron. Now, if this mixture of iron and sulphur is treated with carbon disulphide, the sulphur part dissolves in it leaving the iron unchanged. This means that a mixture of iron filings and sulphur also shows the properties of sulphur. If we combine these two results, we can say that a mixture of iron filings and sulphur shows the properties of both its constituents, iron as well as sulphur. In general we can say that a mixture shows the properties of all the constituents present in it.
3.When iron filings are mixed with sulphur powder to prepare the mixture, heat is neither evolved nor absorbed. In general, energy (in the form of heat, light, etc.) is usually neither given out nor absorbed in the preparation of a mixture. So, the formation of a mixture is a physical change.
4.We can mix any amounts of iron filings and sulphur powder to get mixtures having different compositions. Thus, a mixture of iron filings and sulphur has a variable composition. Since its composition is variable, no definite formula can be given to a mixture of iron filings and sulphur. From this discussion we conclude that the composition of a mixture is variable, the constituents can be present in any proportion by mass. Due to its variable composition, a mixture does not have a definite formula.
5.A mixture of iron filings and sulphur does not melt at a single fixed temperature. From this we conclude that a mixture does not have a definite melting point, boiling point, etc.
6.If we examine the mixture of iron filings and sulphur powder with a magnifying glass, it is found that though the iron particles are quite close to the sulphur particles, at some places there are more of iron particles whereas at other places there are more of sulphur particles. That is, a mixture of iron filings and sulphur is not homogeneous, it is heterogeneous. Though most of the mixtures are heterogeneous, some mixtures called solutions and alloys are, however, homogeneous. From this we conclude that a mixture is usually heterogeneous (except solutions and alloys which are homogeneous mixtures). We will now discuss compounds.

Notes

Matter in Our Surroundings - Notes

1. 11. Metals Usually Have a Silver or Grey Colour