Practical: Elements, Compounds & Mixtures

Aims

1. To observe and compare the properties of compounds and mixtures made up of the same constituent elements.

2. Thus, infer some common characteristics of mixtures and compounds that can be used to distinguish them.

Procedure and Observations

Part A: Investigating a mixture of elements

1. Observe and record the appearance (colour and state) of some iron filings and sulfur powder:

Appearance of iron filings: black, solid (powder)

Appearance of sulfur power: yellow, solid (powder)

2. Observe and record the physical properties of mixture of iron and sulfur.

i. Place a spatula of iron filings and a spatula of sulfur powder on a piece of filter paper. Mix them together,

ii. To form a mixture, can the iron filings and sulfur be mixed in any proportion?

Observation: Yes they can be mixed in any proportion to form a mixture.

iii. Feel the mixture (from the bottom of the filter paper). Does it feel warm?

Observation: No

iv. Move a magnet under the filter paper. Does the magnet separate the mixture of elements?

Observation: Yes, the magnet separates the iron filings from the sulfur powder. The magnet attracts the iron filings, therefore separating the two elements.

v. Add iron and sulfur mixture into a text tube of water. Stir the mixture and then let it stand for a while. Draw and label what you see.

vi. Does water separate the mixture of elements?

Observation: Yes

vii. Do the iron filings and the sulfur act as separate substances or a single substance with water.

Observation: They act as separate substances.

Conclusions:

·      The substances in a mixture can be mixed in any proportion.

·      When a mixture is formed, heat and light are not usually taken in or given out.

·      The mixture can be separated by physical means.

·      The mixture has the properties of its constituent substances.

Part B: Mixture or Compound?

1. Mix one spatula of sulfur and half a spatula of iron filings in a crucible.

2. Cover the crucible with a lid and heat for 10 minutes using a strong flame.

Appearance of the residue after heating:

A black sold remained in the crucible. Before heating, the solid mixture was heterogeneous with specks of yellow and grey.

Does the magnet separate the residue into iron and sulfur?

No.

Add the residue to water. Stir and allow the mixture to stand. Draw and label what you see.

Conclusion: The residue formed is a compound. The elements can no longer be easily separated by physical methods and they lose their original properties – e.g. iron was no longer magnetic when it formed a compound).