CBSE Class 10 Answered

Maam Can you please enlist all the important chemical reactions which are accompanied by a colour change

Asked by sreejuu | 17 May, 2019, 08:03: PM

Expert Answer

Change of colour

Certain chemical reactions are characterised by a change in colour of the reactants.

Examples:

i. When few pieces of iron are dropped into a blue-coloured copper sulphate solution, the blue colour of the solution fades and turns light green.

$Fe with Iron below space space plus stack stack space CuSO subscript 4 with Copper space sulphate below with Blue below space rightwards arrow with blank on top space stack stack FeSO subscript 4 space with Ferrous space sulphate below with Green below plus space Cu with Copper below$

ii. When blue-coloured copper sulphate reacts with hydrogen sulphide gas, black-coloured copper sulphide is formed.

$stack CuSO subscript 4 with Blue below space plus space straight H subscript 2 straight S space rightwards arrow with blank on top space CuS with Black below space plus space space straight H subscript 2 SO subscript 4$

Formation of precipitates

Certain chemical reactions are characterised by the formation of insoluble solid substances called precipitates.

Examples:

i. When a solution of silver nitrate is added to a solution of sodium chloride, a white insoluble substance (precipitate) of silver chloride is formed.

$AgNO subscript 3 space plus space NaCl space rightwards arrow with blank on top space stack AgCl space space space downwards arrow with White space ppt. below space plus space NaNO subscript 3$

ii. When ferrous sulphate solution is added to sodium hydroxide, a dirty green precipitate of ferrous hydroxide is formed.

$stack FeSO subscript 4 with light space Green below space plus space 2 NaOH space rightwards arrow with blank on top stack space Fe left parenthesis OH right parenthesis subscript 2 downwards arrow with Dirty space green space ppt. below plus space Na subscript 2 SO subscript 4$

iii. Lead nitrate decomposes to give yellow lead monoxide, brown nitrogen dioxide and colourless oxygen.

$stack 2 Pb left parenthesis NO subscript 3 right parenthesis subscript 2 with White below space space rightwards arrow stack space 2 PbO with Yellow below space space plus space space 4 NO subscript 2 space space plus space space straight O subscript 2$