Compound

A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion. The composition of each new substance is always fixed. The new substance has totally different properties. Only chemical or electrochemical reactions can separate the constituents. A molecular formula is the short form of a compound’s name, written using the symbols of the elements and the number of atoms in it. 

For example, 

Water (H₂O):

• Contains 2 hydrogen atoms and 1 oxygen atom.
• Molecular formula: H₂O.

Carbon dioxide (CO₂):

• Contains 1 carbon atom and 2 oxygen atoms.
• Molecular formula: CO₂.

Methane (CH₄):

• Contains 1 carbon atom and 4 hydrogen atoms.
• Molecular formula: CH₄.

1. Aim: To understand the difference between a mixture and a compound using iron filings and sulphur powder.

2. Requirements: iron filings, sulphur powder, Bunsen burner or flame source, test tube, tongs, and hydrochloric acid (for additional testing).

3. Procedure

• Group 1: Formation of a Mixture: Mix iron filings and sulphur powder thoroughly. Observe the properties of the mixture.
• Group 2: Formation of a Compound (Iron Sulphide): Mix iron filings and sulphur powder. Heat the mixture strongly until it becomes red hot. Allow the mixture to cool down. Observe the new material formed (iron sulphide).

4. Observations

• Group 1 (Mixture): The mixture retains the individual properties of iron and sulphur. It shows magnetic properties because the iron remains unchanged.
• Group 2 (Compound): After heating, a new compound (iron sulphide) forms with properties different from iron and sulphur. Iron sulphide is non-magnetic and does not react with carbon sulphide, but it reacts with hydrochloric acid to release hydrogen sulphide gas (which smells like rotten eggs).

5. Conclusion

• Mixture (Group 1): The mixture retains the individual properties of both iron and sulphur.
• Compound (Group 2): A new substance (iron sulphide) is formed, with different properties from its components. In a compound, a chemical reaction takes place and the individual properties of the elements are lost.

1. Aim: To observe what happens when sugar is heated and when a magnesium ribbon is burnt. Understand the elements involved in these reactions.

2. Requirements: test tube, sugar, tongs, magnesium ribbon, and flame source (candle or Bunsen burner)

3. Procedure

• Heating Sugar: Take some sugar in a test tube. Heat the test tube gently over a flame. Observe the changes and note what remains in the test tube.
• Burning Magnesium Ribbon: Hold a magnesium ribbon with tongs. Place the ribbon in the flame and observe the reaction.

4. Observations

• Heating Sugar: The sugar melts, loses water, and leaves a black substance (carbon) behind. This shows that sugar is made of carbon, hydrogen, and oxygen (C, H, and O).
• Burning Magnesium Ribbon: The magnesium ribbon burns with a bright white flame, forming white ash (magnesium oxide). Magnesium combines with oxygen from the air to form magnesium oxide (MgO).

5. Conclusion

• Sugar: The black carbon left behind indicates that sugar contains carbon. Sugar is made of three elements: carbon (C), hydrogen (H), and oxygen (O).
• Carbon Dioxide (CO₂): The name implies that it contains one carbon atom (C) and two oxygen atoms (O₂).
• Magnesium: Burning magnesium forms magnesium oxide (MgO), which shows magnesium reacts with oxygen.

Burning of magnesium