Give 2 examples of each of following occuring during a chemical reaction.
(i) Change of state
(ii) change of colour
(iii) evolution of gas
(iv) Formation of precipitate
Answers
1) Change of state.
When was is burnt in the form of wax candlethen water and carbon dioxide is formed. Wax is solid, water is a liquid whereas carbon dioxide is a gas.
2. Keeping water in less than 0° celcius that liquid water changes the state and converts into ice which is solid in state.
2) Change of colour.
1. The reaction between lead nitrate solution and potassium iodide. It changes the color of the reaction to yellow. The following reaction is,
Pb(NO3)2 + 2KI --------->PbI2 + 2KNO3
2. Green colour ferrous sulphate gives red- brown color ferric oxide.
2FeSO4(s) + heat ---------> Fe2O3(s) + SO2(g) + SO3(g).
3) Evolution of gas.
1. The chemical reaction between zinc and dilute sulphuric acid is characterised by the evolution of gas.
Zn(s) + H2SO4(aq) ---------> ZnSO4(aq) + H2(g)
2. When zinc reacts with dilute Hydrochloric acid the hydrogen gas is evolved.
Zn(s) + 2HCl(aq) ----------> ZnCl2(aq) + H2(g)
4) Formation of precipitate.
1. The reaction between barium chloride on sodium sulphate.
BaCl2(aq) + Na2SO4 -------> BaSO4(s) + 2KNaCl(aq)
2. The reaction between potassium chloride and silver nitrate and solid silver chloride is precipitate or insoluble salt is formed.
AgNO3(aq) + KCl(aq) ---------> AgCl (precipitate) KNO3(aq).
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Answer:
1.Evolution of gas:
The chemical reaction between zinc and dilute sulphuric acid is characterized by the evolution of hydrogen gas.
Zn(s)+H
2SO4(aq)→ZnSO
4(aq)+H
2
(g)
2.Change in colour:
The reaction between the lead nitrate solution and potassium iodide solution.
Pb(NO
3
)
2
(aq)+2KI→PbI
2
(s)+2KNO
3
(aq)
In this reaction colour changes from colourless to yellow.
3.Formation of precipitate:
The action of Barium Chloride on sodium sulphate.
BaCl
2
(aq)+Na
2
SO
4
(aq)→BaSO
4
(s)+2KNaCl(aq)
4.Change in temperature:
The action of dilute sulphuric acid on zinc:
Zn(s)+H
2
SO
4
(aq)→ZnSO
4
(s)+H
2
(g)
In this reaction, heat is evolved.
5.Change in the state:
When the wax is burnt in the form of the wax candle then water and carbon dioxide are formed. Wax is solid, water is a liquid whereas carbon dioxide is a gas.