Chemistry
State the changes observed in the following chemical reactions.
(a) A small piece of sodium is dropped in water.
(b) Few iron filings are added to blue copper sulphate solution.
(c) Water is added to quick lime (CaO).
(d) Hydrochloric acid is added to metal sulphide.
Chemical Reaction
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Answer
(a) Sodium reacts vigorously, producing bubbles of hydrogen gas, moving rapidly on the water surface, and often melting into a small ball. The reaction is highly exothermic and may produce a flame.
2Na + 2H2O ⟶ 2NaOH + H2 ↑
(b) The blue colour of copper sulphate solution gradually changes to light green due to the formation of ferrous sulphate. A reddish-brown deposit of copper is formed on the iron filings.
Fe + CuSO4 ⟶ FeSO4 + Cu
(c) Quick lime reacts with water with the evolution of a large amount of heat. A hissing sound may be heard and a white, powdery/pasty substance called slaked lime, Ca(OH)2, is formed.
CaO + H2O ⟶ Ca(OH)2 + Δ
(d) A gas with a rotten egg smell is released, indicating the formation of hydrogen sulphide gas during the reaction.
FeS + 2HCl ⟶ FeCl2 + H2S ↑
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Related Questions
Write the chemical reaction where the following changes are observed.
(a) Gas is evolved
(b) Colour change is noticed
(c) Precipitate is formed
(d) Physical state of reactants is changed
Give a reason for the following :
(a) Silver nitrate solution is kept in coloured bottles.
(b) Molybdenum is used in the manufacture of ammonia.
(c) A blue solution of copper sulphate changes to green when a piece of iron is added to this solution.
(d) Colourless concentrated sulphuric acid in a test tube changes to blue on adding a small piece of copper to it.
State the type of reactions and give one equation in each case.
(a) Two or more reactants combine to form a single product.
(b) A single reactant breaks up into two or more products.
Give an example of each:
Combination reaction in which:
(i) An element of valency 3 combines with nitrogen.
(ii) A non-metal oxide reacting with water to form an acid.
(iii) A metal oxide reacting with water to form its hydroxide.