Distinguishing Between a Mixture and a Compound

The main aim of this experiment is to differentiate between a mixture of two components and a pure compound. A mixture is obtained by mixing two or more components in any proportion. The process of mixing the components is a physical change, as no new substance is formed. The components of a mixture retain their individual properties.

For example, simply mixing iron filings and sulphur powder results in the formation of a mixture.

When a compound is formed by a chemical reaction between two or more components, then each of the components loses its individual properties. This conversion of the components into a new compound is a chemical change. The ratio of components in a compound is fixed.

For example, when a mixture of iron filings and sulphur powder is heated, it results in the formation of ferrous sulphide, a new compound. 

Fe(s) + S(s)  FeS(s)

Apparatus & Materials Required

• Two watch glasses
• China dish 
• Burner 
• Tripod Stand
• Spatula
• Wire gauze 
• Bar magnet
• Test tubes placed in stand
• Filter paper
• Splinter
• Filtration setup
• Sulphur powder
• Iron filings
• Dilute hydrochloric acid
• Lead acetate solution
• Carbon disulphide

Experiment Procedure

Steps to follow the given procedure:

1. Take 5.6 g iron filings and 3.2 g sulphur powder in a watch glass. Mix them properly and label it as A.
2. Take half of this mixture A in a china dish and heat it slowly on a Bunsen burner until a black mass is formed. Cool the contents of the china dish and put the powdered black mass in another watch glass labelled B.
3. Now, move a magnet over sample A and the powdered black mass in sample B several times. Record your observations. 
4. Take small amounts of the mixture from samples A and B in two different test tubes and add 5 mL dil. hydrochloric acid to them. Test the evolved gas by bringing a lighted splinter near the mouth of the test tubes. Record your observations.
5. Also, test the evolved gas by bringing a filter paper dipped in lead acetate solution near the mouth of both the test tubes. Record your observations.
6. Again, take a pinch of A and B in two empty test tubes. Add 5 mL carbon disulphide (CS₂) and shake the mixtures. 
7. Filter both the solutions.
8. Record your observations.

Conclusion

In this experiment, we conclude that:

• The iron filings get attracted towards the magnet, but FeS does not.
• Similarly, sulphur dissolves in CS₂, but FeS does not. 
• Iron filings react with dilute HCl to liberate H₂ gas, however, FeS reacts with dilute HCl to form H₂S gas. 
• Thus, we can conclude that the components present in a mixture retain their individual properties. However, the components present in a compound do not retain their individual properties.

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