Question

Give one example each of a chemical reaction characterised by: evolution of gas, change in colour, formation of a precipitate, change in temperature and change in state
(class 10 CBSE SAMPLE PAPER 2017-18 SCIENCE)

Answer 1

Solution:

1.Evolution of gas:

The chemical reaction between zinc and dilute sulphuric acid is characterized by the evolution of hydrogen gas.
Zn(s) + H2SO4(aq) -------->ZnSO4(aq) + H2(g)

2.Change in colour:

Reaction between lead nitrate solution and potassium iodide solution.
Pb(NO3)2(aq) +2KI -------> PbI2(s) + 2KNO3(aq)
In this reaction colour changes from colourless to yellow.


3.Formation of precipitate:

Action of Barium Chloride on sodium sulphate.
BaCl2 (aq) + Na2SO4 (aq) ------> BaSO4(s)+2NaCl(aq)


4.Change in temperature change in temperature:

Action of dilute sulphuric acid on zinc
Zn(s) + H2SO4(aq) -------->ZnSO4(aq) + H2(g)
In this reaction heat is evolved.


5.Change in state:
When wax is burnt in the form of wax candle then Water and carbon dioxide are formed. Wax is a solid water is a liquid whereas carbon dioxide gas.


HOPE THIS WILL HELP YOU....

Answer 2

Answer:

1. Change in colour :

The reaction between lead nitrate solution and poassium iodide solution.

Chemical equation as follow :

Pb ( NO₃ )₂ + 2 KI  ⇒  PbI₂ + 2 KNO₃

In above reaction colour change from colourless to yellow.

2. Change in temperature :

The reaction between dil. sulphuric acid on zinc.

Chemically :

Zn + H₂SO₄  ⇒  ZnSO₄ + H₂

Heat evolved in the above reaction.

3. Formation of precipitation​ :

The reaction between barium chloride on sodium sulphate.

Chemically :

BaCl₂ + Na₂SO₄  ⇒  BaSO₄ + 2 NaCl

In the above reaction white ppt. of BaSO₄ will form.