##### Class 9^{th} Physics & Chemistry AP Board Solution

**Improve Your Learning**- Draw the diagram to show the experimental setup for the law of conservation of mass.…
- Explain the process and precautions in verifying law of conservation of mass.…
- 15.9g. of copper sulphate and 10.6g of sodium carbonate react together to give 14.2g of…
- Carbon dioxide is added to 112g of calcium oxide. The product formed is 200g of calcium…
- 0.24g sample of compound of oxygen and boron was found by analysis to contain 0.144g of…
- In a class, a teacher asked to write the molecular formula of oxygen Shamita wrote the…
- Imagine what would happen if we do not have standard symbols for elements?…
- Mohith said "H2 differs from 2H". Justify.
- Lakshmi gives a statement "CO and Co both represents element". Is it correct? State…
- The formula of the water molecule is H2O. What information you get from this formula.…
- How would you write 2 molecules of oxygen and 5 molecules of Nitrogen.…
- The formula of a metal oxide is MO. Then write the formula of its chloride.…
- Formula of calcium hydroxide is Ca (OH)2 and zinc phosphate is Zn3(PO4)2. Then write the…
- Find out the chemical names and formulae for the following common household substances. a)…
- 0.5 mole of N2 gas. Calculate the mass of the following
- 0.5 mole of N atoms. Calculate the mass of the following
- 3.011 × 10^23 number of N atoms. Calculate the mass of the following…
- 6.022 × 10^23 number of N2 molecules. Calculate the mass of the following…
- 46g of Na Calculate the number of particles in each of the following…
- 8g of O2 Calculate the number of particles in each of the following…
- 0.1 mole of hydrogen Calculate the number of particles in each of the following…
- 12g of O2 gas. Convert into mole
- 20g of water. Convert into mole
- 22g of carbon dioxide. Convert into mole
- Write the valencies of Fe in FeCl2 and FeCl3
- Calculate the molar mass of Sulphuric acid (H2SO4) and glucose (C6H12O6)…
- Which has more number of atoms - 100g of sodium or 100g of iron? Justify your answer.…
- Complete the following table.
- Fill the following table

**Improve Your Learning**

- Draw the diagram to show the experimental setup for the law of conservation of mass.…
- Explain the process and precautions in verifying law of conservation of mass.…
- 15.9g. of copper sulphate and 10.6g of sodium carbonate react together to give 14.2g of…
- Carbon dioxide is added to 112g of calcium oxide. The product formed is 200g of calcium…
- 0.24g sample of compound of oxygen and boron was found by analysis to contain 0.144g of…
- In a class, a teacher asked to write the molecular formula of oxygen Shamita wrote the…
- Imagine what would happen if we do not have standard symbols for elements?…
- Mohith said "H2 differs from 2H". Justify.
- Lakshmi gives a statement "CO and Co both represents element". Is it correct? State…
- The formula of the water molecule is H2O. What information you get from this formula.…
- How would you write 2 molecules of oxygen and 5 molecules of Nitrogen.…
- The formula of a metal oxide is MO. Then write the formula of its chloride.…
- Formula of calcium hydroxide is Ca (OH)2 and zinc phosphate is Zn3(PO4)2. Then write the…
- Find out the chemical names and formulae for the following common household substances. a)…
- 0.5 mole of N2 gas. Calculate the mass of the following
- 0.5 mole of N atoms. Calculate the mass of the following
- 3.011 × 10^23 number of N atoms. Calculate the mass of the following…
- 6.022 × 10^23 number of N2 molecules. Calculate the mass of the following…
- 46g of Na Calculate the number of particles in each of the following…
- 8g of O2 Calculate the number of particles in each of the following…
- 0.1 mole of hydrogen Calculate the number of particles in each of the following…
- 12g of O2 gas. Convert into mole
- 20g of water. Convert into mole
- 22g of carbon dioxide. Convert into mole
- Write the valencies of Fe in FeCl2 and FeCl3
- Calculate the molar mass of Sulphuric acid (H2SO4) and glucose (C6H12O6)…
- Which has more number of atoms - 100g of sodium or 100g of iron? Justify your answer.…
- Complete the following table.
- Fill the following table

###### Improve Your Learning

**Question 1.**Draw the diagram to show the experimental setup for the law of conservation of mass.

**Answer:**Step 1: Take a flask and take a mixture of sodium hydroxide solution and copper sulphate solution.

Step 2: Weight the flask and note it.

Step 3: Now mix the whole mixture thoroughly.

Step 4: Now, weight the flask.

We will observe that after mixing there is no change in the mass. This explains the law of conservation of mass.

**Question 2.**Explain the process and precautions in verifying law of conservation of mass.

**Answer:**Law of conservation of mass states that “Matter is neither created nor destroys in a chemical reaction. More simply, the mass of products is equal to the mass of reactants in a chemical reaction.

**Question 3.**15.9g. of copper sulphate and 10.6g of sodium carbonate react together to give 14.2g of sodium sulphate and 12.3g of copper carbonate. Which law of chemical combination is obeyed? How?

**Answer:**Law of conservation of mass is obeyed.

__Explanation:__

Total mass of reactants = 15.9g + 10.6g = 26.5g

Total mass of products = 14.2g + 12.3g = 26.5g

__As there is no change in the mass of reactants and products, hence law of conservation is obeyed.__

**Question 4.**Carbon dioxide is added to 112g of calcium oxide. The product formed is 200g of calcium carbonate. Calculate the mass carbon dioxide used. Which law of chemical combination will govern your answer.

**Answer:**The reaction taking place is:

Let the mass of CO_{2} is xg.

__According to the law of conservation of mass, the mass of reactants is equal to the mass of products.__

Therefore,

⇒ x + 112g = 220g

⇒ x = 220g – 112g

⇒ x = 108g

__Thus, the mass of carbon dioxide is 108g.__

**Question 5.**0.24g sample of compound of oxygen and boron was found by analysis to contain 0.144g of oxygen and 0.096g of boron. Calculate the percentage composition of the compound by weight.

**Answer:**Given: Mass of compound = 0.24g

Mass of oxygen = 0.144g

Mass of boron = 0.096g

__To calculate the percent of the composition of oxygen, we apply the formula:__

⇒

⇒ % composition of oxygen = 0.6g × 100

⇒ % composition of oxygen = 60%

__To calculate the percent of the composition of boron, we apply the formula:__

⇒

⇒ % composition of boron = 0.4g × 100

⇒ % composition of boron = 40%

__Total percentage composition of compound is 60% + 40% = 100%__

**Question 6.**In a class, a teacher asked to write the molecular formula of oxygen Shamita wrote the formula as O_{2} and Priyanka as O. which one is correct? State the reason.

**Answer:**Shamita wrote the correct formula of oxygen as O_{2} because:

i. A molecule of oxygen has two atoms.

ii. It is diatomic in nature (atomicity = 2)

iii. Thus, writing oxygen as O_{2} indicates two separate atoms of oxygen.

__Note: Atomicity is the number of atoms constituting a molecule.__

**Question 7.**Imagine what would happen if we do not have standard symbols for elements?

**Answer:**if we do not have standard symbols for elements, then it will take a lot of time to write the full name of the elements and compounds every time to describe a reaction.

**Question 8.**Mohith said "H_{2} differs from 2H". Justify.

**Answer:**

**Question 9.**Lakshmi gives a statement "CO and Co both represents element". Is it correct? State reason.

**Answer:**No, CO does not represent element whereas Co represents element because the first letter of the symbol is always the upper case and the second letter is always lower case.

In CO, the second letter is uppercase whereas in Co, the second letter is lowercase. Hence Co represents an element.

**Question 10.**The formula of the water molecule is H_{2}O. What information you get from this formula.

**Answer:**To get the information, first, we will see the elements present in a molecule of the compound.

Second, we will count the number of atoms of each element of that molecule.

__In H___{2}O:

i. 2 atoms of hydrogen and one atom of oxygen are present.

ii. There are total three atoms present in a molecule of water.

**Question 11.**How would you write 2 molecules of oxygen and 5 molecules of Nitrogen.

**Answer:**__For oxygen:__

⇒ First, write the symbol of oxygen –

⇒ Now write 2 as a subscript after O –

__For nitrogen:__

⇒ First, write the symbol of nitrogen –

⇒ Now write 5 as a subscript after N –

**Question 12.**The formula of a metal oxide is MO. Then write the formula of its chloride.

**Answer:**The formula of its chloride is MOCl_{2}

**Question 13.**Formula of calcium hydroxide is Ca (OH)_{2} and zinc phosphate is Zn_{3}(PO_{4})_{2}. Then write the formula to calcium phosphate.

**Answer:**Valency of Ca = 2

Valency of PO_{4} = 3

__Now, apply the criss cross method__

So the formula will be Ca_{3}(PO_{4})_{2}

**Question 14.**Find out the chemical names and formulae for the following common household substances.

a) common salt

b) baking soda

c) washing soda

d) vinegar

**Answer:**a) __Common salt__

Chemical name – sodium chloride

Chemical formula – NaCl

b) __baking soda__

Chemical name – sodium bicarbonate

Chemical formula – NaHCO_{3}

c) __washing soda__

Chemical name – sodium carbonate

Chemical formula – Na_{2}CO_{3}

d) __vinegar__

Chemical name – acetic acid

Chemical formula – CH_{3}COOH

**Question 15.**Calculate the mass of the following

0.5 mole of N_{2} gas.

**Answer:**__0.5 mole of N___{2} gas

First, we apply the formula:

⇒ Mass of N_{2} = No. of moles × Molar mas of N_{2}

⇒ Mass of N_{2} = 0.5 mole × 2(atomic mass of nitrogen)

⇒ Mass of N_{2} = 0.5 × 2 × 14

⇒ Mass of N_{2} = 14g

__Thus, the mass of N___{2} gas is 14g.

**Question 16.**Calculate the mass of the following

0.5 mole of N atoms.

**Answer:**__0.5 mole of N____atoms__

First, we apply the formula:

⇒ Mass of Natoms = No. of moles × Molar mass of N

⇒ Mass of Natoms = 0.5 mole × (atomic mass of nitrogen)

⇒ Mass of Natoms = 0.5 × 14

⇒ Mass of N_{2} = 7g

__Thus, the mass of N atoms is 7g.__

**Question 17.**Calculate the mass of the following

3.011 × 10^{23} number of N atoms.

**Answer:**__3.011 X 10__^{23} number of N atoms.

As we know that 1 mole = 6.022 X 10^{23}atoms

⇒

⇒ 1/2 mole = 0.5 mole

__For 0.5 mole of N____atoms__

First, we apply the formula:

⇒ Mass of Natoms = No. of moles × Molar mass of N

⇒ Mass of Natoms = 0.5 mole × (atomic mass of nitrogen)

⇒ Mass of Natoms = 0.5 × 14

⇒ Mass of N atoms = 7g

__Thus, mass of____3.011 × 10__^{23} number of N atoms is 7g

**Question 18.**Calculate the mass of the following

6.022 × 10^{23} number of N_{2} molecules.

**Answer:**__6.022 X 10__^{23} number of N_{2} molecules.

As we know that 1 mole = 6.022 X 10^{23}atoms

__For 1 mole of N___{2}__molecules:__

First, we apply the formula:

⇒ Mass of N_{2} = No. of moles × Molar mass of N_{2}

⇒ Mass of N_{2} = 1 mole × 2(atomic mass of nitrogen)

⇒ Mass of N_{2} = 1mole × 28u

⇒ Mass of N_{2} = 28g

__Thus, mass of____6.022 × 10__^{23} number of N_{2} molecules is 28g.

**Question 19.**Calculate the number of particles in each of the following

46g of Na

**Answer:**The number of particles present in one mole of any substance is has a fixed value of 6.022 × 10^{23}. This number is called Avogadro constant(N_{A}).

Mass of Na = 46g

Molar mass of Na = 23u

__Apply the formula given below:__

Number of particles = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of particles = 2 × 6.022 × 10^{23}

^{⇒} Number of particles = 12.046 × 10^{23}

__Thus, 46g of Na contains 12.046 × 10__^{23} particles.

**Question 20.**Calculate the number of particles in each of the following

8g of O_{2}

**Answer:**The number of particles present in one mole of any substance is has a fixed value of 6.022 × 10^{23}. This number is called Avogadro constant(N_{A}).

Mass of O_{2} = 8g

Molar mass of O_{2} = 32u

__Apply the formula given below:__

Number of particles = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of particles = 0.25 × 6.022 × 10^{23}

^{⇒} Number of particles = 1.5 × 10^{23}

__Thus, 8g of O___{2} contains 1.5 × 10^{23} particles.

**Question 21.**Calculate the number of particles in each of the following

0.1 mole of hydrogen

**Answer:**The number of particles present in one mole of any substance is has a fixed value of 6.022 × 10^{23}. This number is called Avogadro constant(N_{A}).

Number of mole of hydrogen = 0.1 mole

Molar mass of H_{2} = 2u

__Apply the formula given below:__

Number of particles = number of moles × 6.022 × 10^{23}

⇒ Number of particles = 0.1 mole × 6.022 × 10^{23}

^{⇒} Number of particles = 6.022 × 10^{24}

__Thus, 0.1 mole of hydrogen contains 6.022 × 10__^{24}particles.

**Question 22.**Convert into mole

12g of O_{2} gas.

**Answer:**Mass of O_{2} gas = 12g

Molar mass of O_{2} = 32u

Apply the formula:

⇒

⇒ No. of moles = 0.37

__Thus, the 12g of O___{2} gas is 0.37 mole

**Question 23.**Convert into mole

20g of water.

**Answer:**Mass of water(H_{2}O) = 20g

Molar mass of H_{2}O = 18u

Apply the formula:

⇒

⇒ No. of moles = 1.11

__Thus, the 20g of water is 1.11 mole__

**Question 24.**Convert into mole

22g of carbon dioxide.

**Answer:**Mass of CO_{2} gas = 22g

Molar mass of CO_{2} = 44u

Apply the formula:

⇒

⇒ No. of moles = 0.5

__Thus, the 22g of CO___{2} gas is 0.5 mole

**Question 25.**Write the valencies of Fe in FeCl_{2} and FeCl_{3}

**Answer:**In FeCl_{2}, the valency of Fe is + 2

In FeCl_{3}, the valency of Fe is + 3

**Question 26.**Calculate the molar mass of Sulphuric acid (H_{2}SO_{4}) and glucose (C_{6}H_{12}O_{6})

**Answer:**__Molar mass of sulphuric acid (H___{2}SO_{4}):

⇒ 2(atomic mass of hydrogen) + (atomic mass of Sulphur) + 4(atomic mass of oxygen)

⇒ 2 × 1 + 32 + 4 × 16

⇒ 2 + 32 + 64

⇒ 98 u

__Thus, the molar mass of H___{2}SO_{4} is 98 u.

__Molar mass of glucose (C___{6}H_{12}O_{6}):

⇒ 6(atomic mass of carbon) + 12(atomic mass of hydrogen) + 6(atomic mass of oxygen)

⇒ 6 × 12 + 12 × 1 + 6 × 16

⇒ 72 + 12 + 96

⇒ 108 u

__Thus, the molar mass of C___{6}H_{12}O_{6} is 108 u.

**Question 27.**Which has more number of atoms - 100g of sodium or 100g of iron? Justify your answer. (atomic mass of sodium = 23u, atomic mass of iron = 56u)

**Answer:**__For sodium__

Given: Mass of sodium = 100g

Molar mass of sodium = 23u

Number of atoms = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of atoms = 4.34 × 6.022 × 10^{23}

^{⇒} Number of atomss = 2.613 × 10^{24}

^{⇒}__Thus, 100g of sodium contains 2.613 × 10__^{24} atoms.

__For iron__

Given: Mass of iron = 100g

Molar mass of iron = 55.8u

Number of atoms = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of atoms = 1.79× 6.022 × 10^{23}

^{⇒} Number of atoms = 1.07× 10^{24}

^{⇒}__Thus, 100g of iron contains 1.07× 10__^{24}__atoms.__

Therefore, 100g of sodium has more number of atoms.

**Question 28.**Complete the following table.

**Answer:**

**Question 29.**Fill the following table

**Answer:**

**Question 1.**

Draw the diagram to show the experimental setup for the law of conservation of mass.

**Answer:**

Step 1: Take a flask and take a mixture of sodium hydroxide solution and copper sulphate solution.

Step 2: Weight the flask and note it.

Step 3: Now mix the whole mixture thoroughly.

Step 4: Now, weight the flask.

We will observe that after mixing there is no change in the mass. This explains the law of conservation of mass.

**Question 2.**

Explain the process and precautions in verifying law of conservation of mass.

**Answer:**

Law of conservation of mass states that “Matter is neither created nor destroys in a chemical reaction. More simply, the mass of products is equal to the mass of reactants in a chemical reaction.

**Question 3.**

15.9g. of copper sulphate and 10.6g of sodium carbonate react together to give 14.2g of sodium sulphate and 12.3g of copper carbonate. Which law of chemical combination is obeyed? How?

**Answer:**

Law of conservation of mass is obeyed.

__Explanation:__

Total mass of reactants = 15.9g + 10.6g = 26.5g

Total mass of products = 14.2g + 12.3g = 26.5g

__As there is no change in the mass of reactants and products, hence law of conservation is obeyed.__

**Question 4.**

Carbon dioxide is added to 112g of calcium oxide. The product formed is 200g of calcium carbonate. Calculate the mass carbon dioxide used. Which law of chemical combination will govern your answer.

**Answer:**

The reaction taking place is:

Let the mass of CO_{2} is xg.

__According to the law of conservation of mass, the mass of reactants is equal to the mass of products.__

Therefore,

⇒ x + 112g = 220g

⇒ x = 220g – 112g

⇒ x = 108g

__Thus, the mass of carbon dioxide is 108g.__

**Question 5.**

0.24g sample of compound of oxygen and boron was found by analysis to contain 0.144g of oxygen and 0.096g of boron. Calculate the percentage composition of the compound by weight.

**Answer:**

Given: Mass of compound = 0.24g

Mass of oxygen = 0.144g

Mass of boron = 0.096g

__To calculate the percent of the composition of oxygen, we apply the formula:__

⇒

⇒ % composition of oxygen = 0.6g × 100

⇒ % composition of oxygen = 60%

__To calculate the percent of the composition of boron, we apply the formula:__

⇒

⇒ % composition of boron = 0.4g × 100

⇒ % composition of boron = 40%

__Total percentage composition of compound is 60% + 40% = 100%__

**Question 6.**

In a class, a teacher asked to write the molecular formula of oxygen Shamita wrote the formula as O_{2} and Priyanka as O. which one is correct? State the reason.

**Answer:**

Shamita wrote the correct formula of oxygen as O_{2} because:

i. A molecule of oxygen has two atoms.

ii. It is diatomic in nature (atomicity = 2)

iii. Thus, writing oxygen as O_{2} indicates two separate atoms of oxygen.

__Note: Atomicity is the number of atoms constituting a molecule.__

**Question 7.**

Imagine what would happen if we do not have standard symbols for elements?

**Answer:**

if we do not have standard symbols for elements, then it will take a lot of time to write the full name of the elements and compounds every time to describe a reaction.

**Question 8.**

Mohith said "H_{2} differs from 2H". Justify.

**Answer:**

**Question 9.**

Lakshmi gives a statement "CO and Co both represents element". Is it correct? State reason.

**Answer:**

No, CO does not represent element whereas Co represents element because the first letter of the symbol is always the upper case and the second letter is always lower case.

In CO, the second letter is uppercase whereas in Co, the second letter is lowercase. Hence Co represents an element.

**Question 10.**

The formula of the water molecule is H_{2}O. What information you get from this formula.

**Answer:**

To get the information, first, we will see the elements present in a molecule of the compound.

Second, we will count the number of atoms of each element of that molecule.

__In H _{2}O:__

i. 2 atoms of hydrogen and one atom of oxygen are present.

ii. There are total three atoms present in a molecule of water.

**Question 11.**

How would you write 2 molecules of oxygen and 5 molecules of Nitrogen.

**Answer:**

__For oxygen:__

⇒ First, write the symbol of oxygen –

⇒ Now write 2 as a subscript after O –

__For nitrogen:__

⇒ First, write the symbol of nitrogen –

⇒ Now write 5 as a subscript after N –

**Question 12.**

The formula of a metal oxide is MO. Then write the formula of its chloride.

**Answer:**

The formula of its chloride is MOCl_{2}

**Question 13.**

Formula of calcium hydroxide is Ca (OH)_{2} and zinc phosphate is Zn_{3}(PO_{4})_{2}. Then write the formula to calcium phosphate.

**Answer:**

Valency of Ca = 2

Valency of PO_{4} = 3

__Now, apply the criss cross method__

So the formula will be Ca_{3}(PO_{4})_{2}

**Question 14.**

Find out the chemical names and formulae for the following common household substances.

a) common salt

b) baking soda

c) washing soda

d) vinegar

**Answer:**

a) __Common salt__

Chemical name – sodium chloride

Chemical formula – NaCl

b) __baking soda__

Chemical name – sodium bicarbonate

Chemical formula – NaHCO_{3}

c) __washing soda__

Chemical name – sodium carbonate

Chemical formula – Na_{2}CO_{3}

d) __vinegar__

Chemical name – acetic acid

Chemical formula – CH_{3}COOH

**Question 15.**

Calculate the mass of the following

0.5 mole of N_{2} gas.

**Answer:**

__0.5 mole of N _{2} gas__

First, we apply the formula:

⇒ Mass of N_{2} = No. of moles × Molar mas of N_{2}

⇒ Mass of N_{2} = 0.5 mole × 2(atomic mass of nitrogen)

⇒ Mass of N_{2} = 0.5 × 2 × 14

⇒ Mass of N_{2} = 14g

__Thus, the mass of N _{2} gas is 14g.__

**Question 16.**

Calculate the mass of the following

0.5 mole of N atoms.

**Answer:**

__0.5 mole of N____atoms__

First, we apply the formula:

⇒ Mass of Natoms = No. of moles × Molar mass of N

⇒ Mass of Natoms = 0.5 mole × (atomic mass of nitrogen)

⇒ Mass of Natoms = 0.5 × 14

⇒ Mass of N_{2} = 7g

__Thus, the mass of N atoms is 7g.__

**Question 17.**

Calculate the mass of the following

3.011 × 10^{23} number of N atoms.

**Answer:**

__3.011 X 10 ^{23} number of N atoms.__

As we know that 1 mole = 6.022 X 10^{23}atoms

⇒

⇒ 1/2 mole = 0.5 mole

__For 0.5 mole of N____atoms__

First, we apply the formula:

⇒ Mass of Natoms = No. of moles × Molar mass of N

⇒ Mass of Natoms = 0.5 mole × (atomic mass of nitrogen)

⇒ Mass of Natoms = 0.5 × 14

⇒ Mass of N atoms = 7g

__Thus, mass of____3.011 × 10 ^{23} number of N atoms is 7g__

**Question 18.**

Calculate the mass of the following

6.022 × 10^{23} number of N_{2} molecules.

**Answer:**

__6.022 X 10 ^{23} number of N_{2} molecules.__

As we know that 1 mole = 6.022 X 10^{23}atoms

__For 1 mole of N _{2}__

__molecules:__

First, we apply the formula:

⇒ Mass of N_{2} = No. of moles × Molar mass of N_{2}

⇒ Mass of N_{2} = 1 mole × 2(atomic mass of nitrogen)

⇒ Mass of N_{2} = 1mole × 28u

⇒ Mass of N_{2} = 28g

__Thus, mass of____6.022 × 10 ^{23} number of N_{2} molecules is 28g.__

**Question 19.**

Calculate the number of particles in each of the following

46g of Na

**Answer:**

The number of particles present in one mole of any substance is has a fixed value of 6.022 × 10^{23}. This number is called Avogadro constant(N_{A}).

Mass of Na = 46g

Molar mass of Na = 23u

__Apply the formula given below:__

Number of particles = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of particles = 2 × 6.022 × 10^{23}

^{⇒} Number of particles = 12.046 × 10^{23}

__Thus, 46g of Na contains 12.046 × 10 ^{23} particles.__

**Question 20.**

Calculate the number of particles in each of the following

8g of O_{2}

**Answer:**

The number of particles present in one mole of any substance is has a fixed value of 6.022 × 10^{23}. This number is called Avogadro constant(N_{A}).

Mass of O_{2} = 8g

Molar mass of O_{2} = 32u

__Apply the formula given below:__

Number of particles = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of particles = 0.25 × 6.022 × 10^{23}

^{⇒} Number of particles = 1.5 × 10^{23}

__Thus, 8g of O _{2} contains 1.5 × 10^{23} particles.__

**Question 21.**

Calculate the number of particles in each of the following

0.1 mole of hydrogen

**Answer:**

The number of particles present in one mole of any substance is has a fixed value of 6.022 × 10^{23}. This number is called Avogadro constant(N_{A}).

Number of mole of hydrogen = 0.1 mole

Molar mass of H_{2} = 2u

__Apply the formula given below:__

Number of particles = number of moles × 6.022 × 10^{23}

⇒ Number of particles = 0.1 mole × 6.022 × 10^{23}

^{⇒} Number of particles = 6.022 × 10^{24}

__Thus, 0.1 mole of hydrogen contains 6.022 × 10 ^{24}particles.__

**Question 22.**

Convert into mole

12g of O_{2} gas.

**Answer:**

Mass of O_{2} gas = 12g

Molar mass of O_{2} = 32u

Apply the formula:

⇒

⇒ No. of moles = 0.37

__Thus, the 12g of O _{2} gas is 0.37 mole__

**Question 23.**

Convert into mole

20g of water.

**Answer:**

Mass of water(H_{2}O) = 20g

Molar mass of H_{2}O = 18u

Apply the formula:

⇒

⇒ No. of moles = 1.11

__Thus, the 20g of water is 1.11 mole__

**Question 24.**

Convert into mole

22g of carbon dioxide.

**Answer:**

Mass of CO_{2} gas = 22g

Molar mass of CO_{2} = 44u

Apply the formula:

⇒

⇒ No. of moles = 0.5

__Thus, the 22g of CO _{2} gas is 0.5 mole__

**Question 25.**

Write the valencies of Fe in FeCl_{2} and FeCl_{3}

**Answer:**

In FeCl_{2}, the valency of Fe is + 2

In FeCl_{3}, the valency of Fe is + 3

**Question 26.**

Calculate the molar mass of Sulphuric acid (H_{2}SO_{4}) and glucose (C_{6}H_{12}O_{6})

**Answer:**

__Molar mass of sulphuric acid (H _{2}SO_{4}):__

⇒ 2(atomic mass of hydrogen) + (atomic mass of Sulphur) + 4(atomic mass of oxygen)

⇒ 2 × 1 + 32 + 4 × 16

⇒ 2 + 32 + 64

⇒ 98 u

__Thus, the molar mass of H _{2}SO_{4} is 98 u.__

__Molar mass of glucose (C _{6}H_{12}O_{6}):__

⇒ 6(atomic mass of carbon) + 12(atomic mass of hydrogen) + 6(atomic mass of oxygen)

⇒ 6 × 12 + 12 × 1 + 6 × 16

⇒ 72 + 12 + 96

⇒ 108 u

__Thus, the molar mass of C _{6}H_{12}O_{6} is 108 u.__

**Question 27.**

Which has more number of atoms - 100g of sodium or 100g of iron? Justify your answer. (atomic mass of sodium = 23u, atomic mass of iron = 56u)

**Answer:**

__For sodium__

Given: Mass of sodium = 100g

Molar mass of sodium = 23u

Number of atoms = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of atoms = 4.34 × 6.022 × 10^{23}

^{⇒} Number of atomss = 2.613 × 10^{24}

^{⇒}__Thus, 100g of sodium contains 2.613 × 10 ^{24} atoms.__

__For iron__

Given: Mass of iron = 100g

Molar mass of iron = 55.8u

Number of atoms = number of moles × 6.022 × 10^{23}

⇒

⇒

⇒ Number of atoms = 1.79× 6.022 × 10^{23}

^{⇒} Number of atoms = 1.07× 10^{24}

^{⇒}__Thus, 100g of iron contains 1.07× 10 ^{24}__

__atoms.__

Therefore, 100g of sodium has more number of atoms.

**Question 28.**

Complete the following table.

**Answer:**

**Question 29.**

Fill the following table

**Answer:**