Chemistry

Important points

1. 1

   The electron was discovered by J.J. Thomson, the proton by Rutherford and the neutron by Chadwick.

2. 2

   The modern periodic table (Moseley) is based on atomic number and has 118 elements.

3. 3

   pH 7 is neutral; below 7 is acidic and above 7 basic. Human blood has a pH of about 7.4.

4. 4

   Baking soda: NaHCO₃; washing soda: Na₂CO₃·10H₂O; bleaching powder: CaOCl₂.

5. 5

   Plaster of Paris is CaSO₄·½H₂O; quicklime is CaO and slaked lime is Ca(OH)₂.

6. 6

   Mercury is the only metal that is liquid at room temperature; bromine is the only liquid non-metal.

7. 7

   Diamond and graphite are allotropes of carbon; graphite conducts electricity.

8. 8

   Brass = copper + zinc; bronze = copper + tin.

9. 9

   Stainless steel is an alloy of iron with chromium and nickel.

10. 10

    Vinegar contains acetic acid, lemon citric acid and curd lactic acid.

11. 11

    Ozone (O₃) in the stratosphere protects Earth from ultraviolet rays.

12. 12

    Helium, the lightest noble gas, is used to fill balloons.

Topic-wise notes

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