Question

class 7th
chapter- physical and chemical change.
Q1. fill in the blanks
a) when baking soda is added to vinegar ................... gas is produced.
b) the formula of rust ..................
c) when carbon dioxide is passed through lime water it turns........................
d) magnesium hydroxide turns red litmus ................... ( blue / red)
e) copper sulphate + iron = .................. +...................
​

Answer 1

Answer:

1 calcium carbonate

2 sodium hydrogen carbonate

3 galvanisation

4 physical

5 chemical

Answer 2

Answer:

A] carbon dioxide.

B] Most rust has the chemical formula FeO2H, also written as FeO (OH)

C] When carbon dioxide is passed through lime water, it turns milky due to formation of white precipitate in form of calcium carbonate.

D]Magnesium hydroxide is a base with the chemical formula Mg(OH)2. Hence, it will turn red litmus paper blue. because metallic oxides are basic in nature. Because oxides are basic in nature.So they turn red litmus to blue.

E] Iron being more reactive than copper will displace copper from its salt and form a subsequent salt of ferrous sulphate. During the reaction, the colour of copper sulphate [blue] will change to greenish-blue {ferrous sulphate}. This is an example of a Displacement reaction.

Explanation: