Atoms And Molecules Class 10th Science Tamilnadu Board Solution

Class 10^th Science Tamilnadu Board Solution

Part-a

1. From the given examples, form the pair of isotopes and the pair of isobars: 18Ar^40 ,…
2. Molecular mass of Nitrogen is 28. Its atomic mass is 14. Find the atomicity of Nitrogen.…
3. Gram molecular mass of Oxygen is 32 g. Density of Oxygen is 1.429 g/litre. Find the gram…
4. ‘Cl’ represents Chlorine atom, ‘Cl2’ represents Chlorine molecule. List out any two…
5. Calculate the gram molecular mass of water from the values of gram atomic mass of Hydrogen…
6. One mole of any substance contains 6.023 x 10^23 particles. If 3.0115 x 10^23 particles…
7. _________ have equal number of neutrons. i) Isobars ii) Isotones iii) Isotopes iv) Mass…
8. Classify the following based on atomicity: i) Chlorine ii) Neon iii) Phosphorous iv) Ozone…
9. Identify and correct the mistake in each of the following: i) The molar volume of gas at…
10. Give a single term substitute for each of the following: i) 6.023 x 10^23 molecules ii)…

Part-b

1. Modern atomic theory takes up the wave concept, principle of uncertainty and other latest…
2. How will you establish the relation between vapour density and molecular mass of a gas by…
3. Calculate the number of moles in: i) 12.046 x 10^23 atoms of Copper ii) 27.95g of Iron…
4. Find the gram molecular mass of the following from the data given: i) H2O ii) CO2 iii)…
5. Complete the table given below:
6. Calculate the number of water molecules present in one drop of water which weighs 0.18 g.…
7. Fill in the blanks using the given data: The formula of Calcium oxide is CaO. The atomic…
8. How many grams are there in: i) 5 moles of water ii) 2 moles of Ammonia iii) 2 moles of…

Part-c

1. When ammonia reacts with hydrogen chloride gas, it produces white fumes of ammonium…
2. Nitro glycerine is used as an explosive. The equation for the explosive reaction is…
3. Sodium bi carbonate breaks down on heating: 2NaHCO3 Na2CO3 + H2O + CO2 (Atomic mass of Na…
4. 40 g of calcium was extracted from 56 g of calcium oxide (Atomic mass of Ca= 40, O=16) i)…
5. How many grams are there in the following? i) 1 mole of chlorine molecule, Cl2 ii) 2 moles…
6. Find how many moles of atoms are there in: i) 2 g of nitrogen. ii) 23 g of sodium iii) 40…

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Part-a

Question 1.

From the given examples, form the pair of isotopes and the pair of isobars:
₁₈Ar⁴⁰, ₁₇Cl³⁵, ₂₀Ca⁴⁰, ₁₇Cl³⁷

Answer:

● Isotopes are the atoms of same chemical element having different

atomic mass. This means they differ in neutron number. For ex- ₁₇Cl³⁵ and ₁₇Cl³⁷. Here both atoms are chlorine atoms and have atomic number 17. So, each atom has 17 electrons and 17 protons. But the former one has atomic mass 35 and the latter one has atomic mass 37. This implies that former one has 18 neutrons (35-17) and latter one has 20 neutrons (37-17). Hence, they are isotopes.

● Isobars are the atoms of different elements having same atomic mass.

This implies that the sum of protons and neutrons in each atom is same. For ex- ₁₈Ar⁴⁰ and ₂₀Ca⁴⁰. Here, the former one is argon atom and latter one is calcium. Their atomic numbers are different. But their atomic mass is same i.e. 40. This implies that the number of nucleons in both atoms is same, even though the proton, electron and neutron numbers are different.

Question 2.

Molecular mass of Nitrogen is 28. Its atomic mass is 14. Find the atomicity of Nitrogen.

Answer:

Atomicity is the number of atoms in the molecule of an element. Molecular mass is calculated by adding up the masses of respective atoms present in the molecule. Nitrogen molecule contains only nitrogen atoms. Given -

Mass of molecule of nitrogen = 28

Mass of atom of nitrogen = 14

Let number of atoms in the molecule = x

So,

Hence, the atomicity of nitrogen is 2. 2 atoms of nitrogen make one

molecule of nitrogen.

Question 3.

Gram molecular mass of Oxygen is 32 g. Density of Oxygen is 1.429 g/litre. Find the gram molar volume of Oxygen.

Answer:

Given - Gram molecular mass of Oxygen = 32 g

Density of Oxygen = 1.429 g/litre

Gram molar volume of Oxygen = ?

Formula used is -

Question 4.

‘Cl’ represents Chlorine atom, ‘Cl₂’ represents Chlorine molecule.

List out any two differences between atoms and molecules.

Answer:

Note –

Atoms combine to form molecules.

Question 5.

Calculate the gram molecular mass of water from the values of gram atomic mass of Hydrogen and of Oxygen.

Gram atomic mass of Hydrogen = 1 g

Gram atomic mass of Oxygen = 16 g

Answer:

If the molecular mass of a given substance is expressed in grams, it is known as gram molecular mass of that substance. Molecular mass is the sum of the atomic masses of all the atoms present in one molecule of the substance.

One molecule of water is H₂O, which contains 2 hydrogen and one oxygen atoms. So, molecular mass is sum of atomic masses of hydrogen and oxygen atoms.

Gram molecular mass of water is 18g.

Question 6.

One mole of any substance contains 6.023 x 10²³particles.
If 3.0115 x 10²³ particles are present in CO₂, find the number of moles.

Answer:

Number of particles in one mole of any substance is 6.023 x 10²³

Note:

1. If a compound or molecular substance is taken, like CO₂, N₂ etc, then 1

mole of the substance contains Avogadro number of molecules. 1 mole contains the mass equal to molecular weight of substance.

2. If a element is taken like C, S, Fe, then 1 mole contains Avogadro

number of atoms. 1 mole contains the mass equal to atomic weight of substance.

Question 7.

_________ have equal number of neutrons.

i) Isobars ii) Isotones

iii) Isotopes iv) Mass Numbers

Answer:

isotones

These are the atoms of different elements with same number of neutrons. Example : ₆C¹³ and ₇N¹⁴

Number of neutrons is obtained by subtracting atomic number from atomic mass number.

Number of neutrons in ₆C¹³ is (13-6) 7.

Number of neutrons in ₇N¹⁴ is (14-7) 7.

● Isobars are the atoms of different elements having same mass number but different atomic numbers.

● Isotopes are the atoms of same element with same atomic number but

different mass number.

● Mass numbers is the sum of protons and neutrons.

Question 8.

Classify the following based on atomicity:

i) Chlorine ii) Neon

iii) Phosphorous iv) Ozone

Answer:

● chlorine is diatomic because its molecule contains 2 atoms of chlorine. Cl₂

● neon is monoatomic because its molecule contains 1 atom of neon. Ne

● Phosphorous is polyatomic because its molecule contains 4 atoms of

phosphorous. If a molecule contains more than 3 atoms in its molecule its polyatomic. P₄

● ozone is triatomic because its molecule contains 3 atoms of oxygen. O₃

Question 9.

Identify and correct the mistake in each of the following:
i) The molar volume of gas at STP is 22.4 cm³.

ii) 2 x R.M.M. = V.D.

iii) An atom cannot exist independently.

iv) The ratio of atoms in a molecule may be integral or simple or may not be fixed.

v) H₂O is a homo atomic molecule.

Answer:

(i) The molar volume of gas at STP is 22.4 litres (not cm³.)

(ii) 2 x V.D = R.M.M

(iii) An atom may or may not exist independently. Atoms like Fe, Na

can exist independently.

(iv) The ratio of atoms in a molecule may be fixed and integral but

may not be simple.

(v) H₂O is a hetero atomic molecule. It contains more than one type

of atoms i.e hydrogen and oxygen. So, it’s a hetero atomic molecule , not homo atomic molecule.

Question 10.

Give a single term substitute for each of the following:

i) 6.023 x 10²³ molecules ii) 22.4 litres of gas at STP

iii) 1/12th part of the mass of one atom of carbon

iv) The half of relative molecular mass

v) Molecular mass / atomic mass

Answer:

(i) 1 mole of a compound or molecular substance / Avogadro number of molecules.

(ii) Molar volume

(iii) One atomic mass unit

(iv) Vapour density

(v) atomicity

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Part-b

Question 1.

Modern atomic theory takes up the wave concept, principle of uncertainty and other latest discoveries to give a clear-cut picture about an atom. State the findings of modern atomic theory.

Answer:

● An atom is the smallest particle which takes part in chemical reaction.

● An atom is considered to be a divisible particle.

● The atoms of the same element may not be similar in all respects.

ex: Isotopes (₁₇Cl³⁵, ₁₇Cl³⁷ )

● The atoms of different elements may be similar in some respects.

ex. Isobars ( ₁₈Ar⁴⁰ , ₂₀Ca⁴⁰ )

● The ratio of atoms in a molecule may be fixed and integral but may not be simple. Ex.C₁₂H₂₂O₁₁ is not a simple ratio. (Sucrose)

● The atoms of one element can be changed into the atoms of another element by transmutation.

● The mass of an atom can be converted into energy. This is in accordance with Einstein’s equation E = mc² where E = energy, m = mass and c = velocity of light

Question 2.

How will you establish the relation between vapour density and molecular mass of a gas by applying Avogadro’s law?

Answer:

Relative Molecular Mass: It is defined as the ratio of the mass of 1 molecule of the gas or vapour to the mass of 1 atom of hydrogen.

Vapour Density (V.D): It is defined as the ratio of the mass of a certain volume of the gas or vapour to the mass of the same volume of hydrogen at the same temperature and pressure.

Applying Avogadro’s Law,

Since hydrogen is diatomic,

2 x V.D = relative molecular mass of a gas or vapour

2 x Vapour density = Relative molecular mass

Question 3.

Calculate the number of moles in:
i) 12.046 x 10²³ atoms of Copper

ii) 27.95g of Iron

iii) 1.51 x 10²³molecules of CO₂

Answer:

we know that to find the number of moles, the following formulae are used:

(i) Using formula 3,

So, 2 moles of copper contain 12.046 x 10²³ atoms of copper.

(ii) Using formula 1,

So, 0.5 moles consist of 27.95 grams of iron.

(iii) Using formula 4,

So, 0.25 moles of CO₂ consists of 1.51 x 10²³ molecules.

Note:

1. If a compound or molecular substance is taken, like CO₂, N₂ etc, then 1

a mole of the substance contains Avogadro number of molecules. 1 mole contains the mass equal to the molecular weight of the substance.

2. If an element is taken like C, S, Fe, then 1 mole contains Avogadro

number of atoms. 1 mole contains the mass equal to the atomic weight of the substance.

Question 4.

Find the gram molecular mass of the following from the data given:

i) H₂O ii) CO₂ iii) NaOH iv) NO₂ v) H₂SO₄

Answer:

Molecular mass is the sum of the atomic masses of all the atoms present in one molecule of the substance.

1. H₂O = (1gX2) + 16g = 18g

2. CO₂ = 12g + (2 x16g) = 12 + 32 = 44g

3. NaOH = 23g + 16g + 1g = 40g

4. NO₂ = 14 + (2 x 16) = 46g

5. H₂SO₄ = (1gx2) + 32g + (4x16g) = 98g

Question 5.

Complete the table given below:

Answer:

Formula used is

So, the complete table is

Question 6.

Calculate the number of water molecules present in one drop of water which weighs 0.18 g.

Answer:

According to mole concept we know that gram molecular weight of any compound consists of Avogadro number of molecules.

This implies that 18 grams of water consists 6.023 x 10²³ molecules of water.

18 grams  6.023 x 10²³ molecules

0.18 grams ?

Question 7.

Fill in the blanks using the given data:
The formula of Calcium oxide is CaO. The atomic mass of Ca is 40, Oxygen is 16 and Carbon is 12.

i) 1 mole of Ca ( ____g) and 1 mole of Oxygen atom ( ___g) combine to form _____mole of CaO ( ____g).

ii) 1 mole of Ca ( ___g) and 1 mole of C ( ___g) and 3 moles of Oxygen atom ( ___g) combine to form 1 mole of CaCO₃ ( ___g)

Answer:

i) 1 mole of Ca ( 40 g) and 1 mole of an Oxygen atom ( 16 g) combine to form 1 mole of CaO ( 56 g).

ii) 1 mole of Ca ( 40 g) and 1 mole of C ( 12 g) and 3 moles of an Oxygen atom ( 3x16 = 48 g) combine to form 1 mole of CaCO₃ ( 100 g)

Note:

1. If a compound or molecular substance is taken, like CO₂, N₂ etc, then 1

a mole of the substance contains Avogadro number of molecules. 1 mole contains the mass equal to the molecular weight of the substance.

2. If an element is taken like C, S, Fe, then 1 mole contains Avogadro

number of atoms. 1 mole contains the mass equal to the atomic weight of the substance.

So, 1 mole of Ca is 40 grams, 1 mole of O atom is 16 grams and 1 mole of C is 12 grams of C. 1 mole of CaO is 56 grams (40+16) of CaO and 1 mole of CaCO₃ is 100 grams ( 40+12+48).

Question 8.

How many grams are there in:

i) 5 moles of water

ii) 2 moles of Ammonia

iii) 2 moles of Glucose

Answer:

we know that in the case of compounds –

Molecular mass of water (H₂O) = (2 + 16 ) = 18 grams

Molecular mass of ammonia (NH₃) = ( 14+3) = 17 grams

Molecular mass of glucose ( C₆H₁₂O₆) = ( 72 + 12+ 96) = 180 grams

Applying the above formula to all 3 cases-

(i) Mass = 5 x 18 = 90 grams

(ii) Mass = 2 x 17 = 34 grams

(iii) Mass = 2 x 180 = 360 grams

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Part-c

Question 1.

When ammonia reacts with hydrogen chloride gas, it produces white fumes of ammonium chloride. The volume occupied by NH₃ in glass bulb A is three times more than the volume occupied by HCl in glass bulb B at STP.



i) How many moles of ammonia are present in glass bulb A?

ii) How many grams of NH₄Cl will be formed when the stopper is opened?

(Atomic mass of N = 14, H = 1, Cl = 35.5)

iii) Which gas will remain after completion of the reaction?

iv) Write the chemical reaction involved in this process.

Answer:

(i) 3 moles

(ii) 53.5 grams (14 + 4 + 35.5)

(iii) Ammonia ( 2 moles will be remaining )

(iv) NH₃ + HCl  NH₄Cl

Explanation -1 mole of any gas at STP occupies 22.4 litres of volume. So, 1 mole of ammonia occupies 22.4 litres of volume. 67.2 litres (22.4 x 3) of volume is 3 moles of ammonia. 22.4 litres of HCl is 1 mole of HCl. According to reaction ,1 mole of ammonia reacts with 1 mole of HCl to form 1 mole of NH₄Cl, which comes out as white fumes.

NH₃ + HCl  NH₄Cl

Even though 3 moles of ammonia is present in bulb, only one 1 mole undergoes reaction with 1 mole of HCl. The other 2 moles of ammonia remain unreacted.

Question 2.

Nitro glycerine is used as an explosive. The equation for the explosive reaction is

4C₃H₅((NO₃))₃12CO₂ + 10H₂O + 6N₂ + O₂

(l) (g) (l) (g) (g)

(Atomic mass of C = 12, H = 1, N = 14, O=16)

1. How many moles does the equation show for i) Nitroglycerine ii) gas molecules produced?

2. How many moles of gas molecules are obtained from 1 mole of nitroglycerine?

3. What is the mass of 1 mole of nitroglycerine?

Answer:

1. 4 moles of nitroglycerine ; CO₂ (12) + N₂(6) + O₂(1) = 19 moles of

gas molecules are formed.

2. 4 moles of nitroglycerine gives 19 moles of gas molecules. So, 1 mole

of nitroglycerine gives (19/4) 4.75 moles of gas molecules.

3. Gram molecular mass of nitroglycerine is 1 mole of nitroglycerine.

So, mass of 1 mole of nitroglycerine is 227 grams.

[(3x12)C + (5x1)H + (3x14)N + (9x16)O]

Question 3.

Sodium bi carbonate breaks down on heating:

2NaHCO₃ Na₂CO₃ + H₂O + CO₂

(Atomic mass of Na = 23, C = 12, H = 1, O=16)

i) How many moles of sodium bi carbonate are there in the equation?

ii) What is the mass of sodium bicarbonate used in this equation?

iii) How many moles of carbon dioxide are there in this equation?

Answer:

(i) Two (coefficient of sodium bi carbonate)

(ii) 1 mole of sodium bi carbonate contains 84 grams. Two moles of

sodium bi carbonate contains 168 grams. So, 168 grams of sodium bi carbonate is used in the equation.

(iii) 1 mole (coefficient of CO₂ )

Question 4.

40 g of calcium was extracted from 56 g of calcium oxide

(Atomic mass of Ca= 40, O=16)

i) What mass of oxygen is there in 56 g of calcium oxide?

ii) How many moles of oxygen atoms are there in this?

iii) How many moles of calcium atoms are there in 40 g of calcium?

iv) What mass of calcium will be obtained from 1000 g of calcium oxide?

Answer:

(i) 16 grams of O

(ii) 1 mole of oxygen atoms

(iii) 1 mole

(iv) 714.38 grams.

56 grams of CaO gives 40 grams of Ca. 1000 grams of CaO gives (1000x40)/56 = 714.28 grams of calcium

Explanation –

CaO  Ca + O

56 40 16

1 mole of any compound (or gas in molecular form) contains the mass equal to its gram molecular mass. 1 mole of any element contains the mass equal to its gram atomic mass. So,

1 mole of CaO = 40 + 16 = 56 grams

1 mole of Ca = 40 grams

1 mole of oxygen atoms = 16 grams

1 mole of calcium oxide dissociates to form 1 mole of Ca and 1 mole of O atoms.

Question 5.

How many grams are there in the following?

i) 1 mole of chlorine molecule, Cl₂

ii) 2 moles of sulphur molecules, S₈

iii) 4 moles of ozone molecules, O₃

iv) 2 moles of nitrogen molecules, N₂

Answer:

we know that when gases are present in the molecular form, 1 mole of any gas is equal to 6.023 x 10²³ molecules of that gas, which is equal to the gram molecular weight of gas in the combined state.

(i) 1 mole of chlorine molecules contains 71 grams of Cl₂. (2×35.5)

(ii) 2 moles of sulphur molecules contain 512 grams of S₈. (2×32×8)

(iii) 4 moles of ozone molecules contain 192 grams of O₃. (4× 16× 3)

(iv) 2 moles of nitrogen molecules contain 56 grams of N₂. (2× 14× 2)

Question 6.

Find how many moles of atoms are there in:

i) 2 g of nitrogen.

ii) 23 g of sodium

iii) 40 g of calcium.

iv) 1.4 g of lithium

v) 32 g of sulphur.

Answer: 

We know the formula that

Applying the above formula for all cases.

(i) 

(ii) 

(iii) 

(iv) 

(v)