Comparing Elements, Compounds & Mixtures

This was a practical session at the lab where we explored and saw the differences between compounds and mixtures ourselves by means of a few simple experiments.

Aim:

• To observe and compare the properties of mixtures and compounds that are made up of the same elements.
• To determine some common characteristics of all compounds and mixtures.

Apparatus:

• Filter Paper
• Test-tube
• Magnet
• Sulfur powder
• Iron filings
• Spatula
• Bunsen burner

Procedure:

Part A:

• Place a spatula of iron filings and a spatula of sulfur powder on a piece of filter paper.
• Mix them together and observe changes in physical appearance and the composition of both elements.

          --> Observation: The mixture has the same colour as original constituents (dark grey and yellow). The composition of the iron filings and sulfur in the mixture is not fixed and can be added in any proportion.

• Feel the temperature of the mixture. Observe whether is it has changed.

          -->Observation: The temperature remains unchanged. (room temperature)

• Move the magnet under the filter paper and observe whether the mixture is attracted to the magnet.

          --> The whole mixture is not attracted to the magnet. Instead, the iron filings, is the only element attracted and thus, separates from the sulfur powder and moves with the magnet.

• Add the mixture of iron filings and  sulfur powder to a test-tube of water.
• Stir the mixture and wait until the mixture rests.
• Observe whether the mixture is separated and whether it is floating.

          -->Observation: The mixture is separated. Sulfur powder floats on water while the iron filings sink in water, acting as two separate elements again. Heat or light isn't taken in or given out when a mixture is formed.

Concluding observations: The mixture retains the properties of its constituent elements. The mixture can be separated by physical means.

Part B:

• Mix precisely one spatula of sulfur and half a spatula of iron filings in a crucible.
• Cover the crucible with a lid and heat it using a Bunsen burner for 10 minutes over a strong non-luminous flame.
• After heating, scrap the residue onto a filter paper and move a magnet underneath.
• Observe whether the substance is attracted to the magnet.

          -->Observation: The substance is not separated and is not attracted by the magnet.

• Place the residue in a test-tube of water and observe.

          -->Observation: The residue is not separated and it sinks in water.

Concluding observations: The resulting substance formed is a compound. Iron and sulfur have gone through a chemical reaction(as heat was taken in while the substance was formed) to form the compound-Copper(II)Sulfide. It does not possess the properties of the constituent elements and is not separated by physical means (constituent element, iron was not attracted by the magnet and sulfur did not float in water alone).

Conclusion:
There are several differences between a compound and a mixture. These are:

1. A mixture does not need to go through a chemical reaction to be formed but a compound needs to go through a chemical reaction to be formed.
2. A mixture retains the properties of its constituent elements but a compound does not possess the properties of the constituents and instead, has new and different characterisitics of its own.
3. A mixture can be separated easily by physical means but a compound cannot be separated by physical means and has to go through chemical means for the chemical reaction to be reversed.

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