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ICSE Class 9 Answered

Give 2 examples of each of the following changes occurring during a chemical reaction : 1) Change of state of the reactants  2)Change of colour  3)Evolution of gas  4) Formation of precipitate 
Asked by 05sumanlata | 19 May, 2019, 11:27: AM
answered-by-expert Expert Answer
Characteristics of chemical reaction:
 
1) Change of state of the reactants:
 
     Example:
 
Ammonia gas reacts with hydrogen chloride gas to produce solid ammonium chloride.
 
NH subscript 3 subscript open parentheses straight g close parentheses end subscript end subscript space plus space HCl subscript open parentheses straight g close parentheses end subscript space space space rightwards arrow with space space space space space space on top space space NH subscript 4 Cl subscript open parentheses straight s close parentheses end subscript
 
2)Change of colour 
 
Example:
 
Wehne few pices of Fe are added to the blue copper sulphate solution, the colour of the solution fades
and turns into light green due to the formation of ferrous sulphate.
 
Fe subscript open parentheses straight s close parentheses end subscript space space plus space CuSO subscript 4 subscript open parentheses aq close parentheses end subscript end subscript space rightwards arrow with space space space on top space space FeSO subscript 4 subscript open parentheses aq close parentheses end subscript end subscript space space space plus space space Cu subscript open parentheses straight s close parentheses end subscript
 
3)Evolution of gas 
 
Example:
 
Zn space plus space space straight H subscript 2 SO subscript 4 space space end subscript space rightwards arrow with space space space space on top space ZnSO subscript 4 space space space plus space space straight H subscript 2 space upwards arrow
 
4) Formation of precipitate

  Example:

When silver nitrate is added to sodium chloride, white insoluble precipitate of silver chloride is formed.

AgNO subscript 3 subscript open parentheses aq close parentheses end subscript space plus space space NaCl subscript aq space space space space rightwards arrow with space space space space on top space space space AgCl subscript open parentheses ppt close parentheses end subscript space downwards arrow space plus space NaNO subscript 3 subscript open parentheses aq close parentheses end subscript end subscript
 
When ferrous sulphate solution is added to the sodium hydroxide, a dirty green precipitate ferrous hydroxide is formed.
 
FeSO subscript 4 subscript open parentheses aq close parentheses end subscript end subscript space space plus space space 2 NaOH subscript open parentheses aq close parentheses end subscript space space rightwards arrow with space space on top space space space Fe open parentheses OH close parentheses subscript 2 space downwards arrow space space plus space Na subscript 2 SO subscript 4 subscript open parentheses aq close parentheses end subscript
 

Answered by Varsha | 20 May, 2019, 09:40: AM
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