Question

Define the following terms
Galvanization, b. Valency c. Rusting
II. Fill in the blanks
1. A change in which the composition of a substance changes is called----------------
2. Salt obtained from sea water can be purified by the process of-------------------
3. Iron forms rust when it reacts with
a. hydrogen and oxygen b. oxygen and moisture( water)
c. carbon dioxide and hydrogen d. water and carbon dioxide
4.The steps involved in writing the chemical formula of a substance are given below:
i.write the symbols of the elements.
ii. if the valencies are identical, cancel the valencies.
iii. write the valency of the elements.
iv. if the valencies are different, criss- cross and place them with reference to the symbol.
which of these is the correct sequence of writing the chemical formula?
a. I,ii,iii,iv. B.i,iii,ii,iv. C.i,iv,ii,iii. D.i,iii,iv,ii.​

Answer 1

$\LARGE\underline{\red{\sf{Required\:answer:-}}}$

1. Galvanization : The process of applying layers like coating zinc , iron (or) steel to prevent rusting.

Valency : The combining capacity of an element is said to be valency.

Rusting : Metals when exposed to atmosphere they reactbeith the dirt and moisture and form compounds. Due to this reaction a layer is formed on the metal.

2. A change in which the composition of a substance changes is called a Chemical Change .

3. Salt obtained from sea water can be purified by the process of Crystallization

4. Iron forms rust when it reacts with

a. hydrogen and oxygen

b. oxygen and moisture( water)

c. carbon dioxide and hydrogen

d. water and carbon dioxide

Option(b) is the required answer.

5. The steps involved in writing the chemical formula of a substance are given below:

i. write the symbols of the elements.

ii. if the valencies are identical, cancel the valencies.

iii. write the valency of the elements.

iv. if the valencies are different, criss- cross and place them with reference to the symbol.

which of these is the correct sequence of writing the chemical formula?

a. I,ii,iii,iv.

B.i,iii,ii,iv.

C.i,iv,ii,iii.

D.i,iii,iv,ii.

Option(D) is the required answer.

Answer 2

Question

Define the following terms

Galvanization - Galvanization is the way to deposit a layer of a metal like chromium or zinc on iron . This process of depositing a layer of zinc on iron is called galvanisation .

like - The iron pipes we use in our homes to carry water are galvanised to prevent rusting.

Valency - The number of electrons gained or lost by an atom of an element for attaining stable octet is called valency.

Rusting - When the metal react with oxygen and water a brownish substance form in it which is rust and this process is known as rusting

• Fe + O2 → Fe2O3

• Fe2O3 + H2O → Fe2O3.xH2O

★ For rusting, the presence of both oxygen and water (or water vapour) is essential .

$\rule{300}{1}$

1. A change in which the composition of a substance changes is called a Chemical Change .

• A change in which one or more new substances are formed is called a chemical change chemical change.

• A chemical change is also called a chemical reaction .

$\rule{300}{1}$

2. Salt obtained from sea water can be purified by the process of Crystallization .

• Some substances can be obtained in pure state from their solutions by crystallisation.

$\rule{300}{1}$

3. Iron forms rust when it reacts with

a. hydrogen and oxygen

b. oxygen and moisture( water) ☑

c. carbon dioxide and hydrogen

d. water and carbon dioxide

★ For Rusting the presence of both oxygen and water (or water vapour) is essential .

$\rule{300}{1}$

4. The steps involved in writing the chemical formula of a substance are given below:

i. write the symbols of the elements.

ii. if the valencies are identical, cancel the valencies.

iii. write the valency of the elements.

iv. if the valencies are different, criss- cross and place them with reference to the symbol.

which of these is the correct sequence of writing the chemical formula?

a. I,ii,iii,iv.

B.i,iii,ii,iv.

C.i,iv,ii,iii.

D.i,iii,iv,ii. ☑

i. write the symbols of the elements.

iii. write the valency of the elements.

iv. if the valencies are different, criss- cross and place them with reference to the symbol.

ii. if the valencies are identical, cancel the valencies.

✔ Don' t get it... Never Mind ! I will explain.

Lets take an example ( we need to write chemical formula of calcium phosphate )

so , according to

⠀

1st step , write the symbols of the elements.

⠀⠀⠀⠀⠀⠀ Calcium⠀⠀⠀⠀phosphate

Symbols -⠀ Ca⠀⠀⠀⠀⠀⠀⠀⠀PO4

⠀

2nd step , write the valency of the elements.

⠀⠀⠀⠀⠀⠀ Calcium⠀⠀⠀⠀phosphate

Symbols -⠀ Ca⠀⠀⠀⠀⠀⠀⠀⠀PO4

valency -⠀⠀2⠀⠀⠀⠀⠀⠀⠀⠀⠀3

⠀

3rd step , if the valencies are different, criss- cross and place them with reference to the symbol.

⠀⠀⠀⠀⠀⠀ Calcium⠀⠀⠀⠀phosphate

Symbols -⠀ Ca⠀⠀⠀⠀⠀⠀⠀⠀PO4

valency -⠀⠀2⠀⠀⠀⠀↗↖⠀⠀⠀⠀3

⠀

4th step , if the valencies are identical, cancel the valencies.

⠀⠀⠀⠀⠀⠀ Calcium⠀⠀⠀⠀phosphate

Symbols -⠀ Ca⠀⠀⠀⠀⠀⠀⠀⠀PO4

valency -⠀⠀2⠀⠀⠀⠀↗↖⠀⠀⠀⠀3

Chemical formula - Ca3(PO4)2