Page 136 - ICSE Chemistry 8

• Reac on between chlorine and hydrogen sulphide: Chlorine reacts with hydrogen sulphide to
form hydrogen chloride and sulphur. Hydrogen is added to chlorine to form hydrogen chloride
(reduc on). Hydrogen is removed from hydrogen sulphide to form sulphur (oxida on).
reduc on
addi on of hydrogen
Cl 2 + H S 2HCl + S
2
Chlorine Hydrogen sulphide Hydrogen chloride Sulphur
removal of hydrogen
oxida on
Substance oxidised: H S Oxidising agent: Cl 2
2
Substance reduced: Cl Reducing agent: H S
2
2
Some more examples are listed here.
Heat
• ZnO + C Zn + CO
Zinc oxide Carbon Zinc Carbon monoxide

• SO 2 + 2H S 2H O + 3S
2
2
Sulphur dioxide Hydrogen sulphide Water Sulphur

Take a Break!

Fill in the blanks.
1. A combina on reac on is also called ______________ reac on.

2. The decomposi on brought about by heat is called ______________________.
3. A more reac ve metal displaces a less reac ve metal during a ________________ reac on.
4. The chemical reac on in which an insoluble part called _____________ separates from the solu on
is called ________________ reac on.

5. ________________ or ________________ is applied on the aff ected area to neutralise the eff ect
of an ant or a bee s ng.
6. The addi on of oxygen or the removal of hydrogen from a substance is called _____________.

7. An atom or a group of atoms which loses electrons during a chemical reac on is called
______________.
8. Chlorine reacts with hydrogen sulphide to form _____________ and _____________.

REACTIVITY OR ACTIVITY SERIES OF METALS

Some metals are chemically very reac ve whereas others are less reac ve or unreac ve. On the basis of
vigour of reac on of various metals with oxygen, water and acids, metals have been arranged in a group
or series.

The arrangement of metals in a ver cal column in the order of their decreasing reac vity is called reac vity
or ac vity series of metals. In reac vity series, the most reac ve metal is placed at the top whereas the
least reac ve metal is placed at the bo om.

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