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# Frank solutions for Class 10 Chemistry chapter 5 - Mole Concept And Stoichiometry

## Chapter 5: Mole Concept And Stoichiometry

Exercise

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Pages 115 - 117]

Exercise | Q 1.1 | Page 115

Prove the Following :
Oxygen is a diatomic molecule.

Exercise | Q 1.2 | Page 115

Prove the Following :
2 X V.D. = Molecular mass.

Exercise | Q 1.3 | Page 115

Prove the Following :
One mole of any gas contains th e same number of molecules.

Exercise | Q 2.1 | Page 115

State : Gay-Lussac's law of combining volumes.

Exercise | Q 2.1 | Page 115

Exercise | Q 3.1 | Page 115

Define atomicity of a gas.

Exercise | Q 3.2 | Page 115

Differentiate between 2H and H2

Exercise | Q 4 | Page 115

When stating the volume of a gas, the pressure and temperature should also be given. Why?

Exercise | Q 5.1 | Page 115

The relative atomic mass of Cl atom is 35.5 a.m.u. Explain this statement.

Exercise | Q 5.2 | Page 115

What is the value of Avogadro's number?

Exercise | Q 5.3 | Page 115

What is the value of molar volume of a gas at STP?

Exercise | Q 6.1 | Page 115

Define the term: Vapour density.

Exercise | Q 6.2 | Page 115

Define the term : Molar volume.

Exercise | Q 6.3 | Page 115

Define the term : Relative atomic mass.

Exercise | Q 6.4 | Page 115

Define the term : Avogadro's number

Exercise | Q 7.1 | Page 115

What are the main applications of Avogadro's law?

Exercise | Q 7.2 | Page 115

How does Avogadro's law explain Gay - lussac's law of combining volumes?

Exercise | Q 7.2 | Page 117

The empirical formula of a compound is C2H5. Its vapour density is 29. Determine the relative molecular mass of the compound and hence its molecular formula.

Exercise | Q 8.1 | Page 115

Explain the term : Gram atom

Exercise | Q 8.2 | Page 115

Explain the term : Gram mole

Exercise | Q 8.3 | Page 115

Explain the term : Mole

Exercise | Q 9.1 | Page 115

Calculate the relative molecular mass of Potassium chlorate.
(use K = 39, Cl = 35.5, O = 16, C = 12, H = 1, Na = 23, N = 14, S=32)

Exercise | Q 9.2 | Page 115

Calculate the relative molecular mass of Sodium acetate
(use K = 39, Cl = 35.5, O = 16, C = 12, H = 1, Na = 23, N = 14, S= 32)

Exercise | Q 9.3 | Page 115

Calculate the relative molecular mass of Ammonium sulphate.
(use K = 39, Cl = 35.5, O = 16, C = 12, H = 1, Na = 23, N = 14, S= 32)

Exercise | Q 9.3 | Page 115

Calculate the relative molecular mass of Chloroform.
(use K = 39, Cl = 35.5, O = 16, C = 12, H = 1, Na = 23, N = 14, S= 32)

Exercise | Q 10 | Page 115

Explain the terms empirical formula and molecular formula.

Exercise | Q 11.1 | Page 115

Give the empirical formula of : C6H6

Exercise | Q 11.2 | Page 115

Give the empirical formula of: C6H12O6

Exercise | Q 11.3 | Page 115

Give the empirical formula of : C2H2

Exercise | Q 11.4 | Page 115

Give the empirical formula of: CH3COOH

Exercise | Q 12 | Page 115

Give three pieces of information conveyed by the formula H2O.

Exercise | Q 13 | Page 115

What do you understand by the term mole? How many elementary units are in one mole of a substance?

Exercise | Q 14.1 | Page 115

Fill in the blank.
Molecular weight of a gas is twice its __________.

Exercise | Q 14.2 | Page 115

Fill in the blank
Mass of 22.4 litre of a gas at STP is __________.

Exercise | Q 14.3 | Page 115

Fill in the blank
One gram atom of an element contains ______ atoms.

Exercise | Q 14.4 | Page 115

Fill in the blank.
One a.m.u. is the mass of ______ atom of C12.

Exercise | Q 14.5 | Page 115

Fill in the blank
Avogadro's number is equal to ______

Exercise | Q 15.1 | Page 115

Give example of compound whose:
Empirical formula is the same as the molecular formula.

Exercise | Q 15.2 | Page 115

Give example of compound whose:
Empirical formula is different from the molecular formula.

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 116]

Exercise | Q 1 | Page 116

Nitrogen and oxygen gas react as illustrated by the equation given below: N2 + O2 → 2NO
Calculate the volume of each reacting gas required to produce 1400cm3 of nitric oxide.

Exercise | Q 2 | Page 116

Calculate the number of molecules in 12.8g of sulphur dioxide gas. Take Avogadro's number as 6 x 1023.
[S = 32, 0 = 16 ]

Exercise | Q 3 | Page 116

Calculate the weight of one molecule of oxygen .
[Avogadro's number = 6 x 1023, O = 16 ]

Exercise | Q 4 | Page 116

Calculate the percentage composition of oxygen in lead nitrate [Pb(NO3)2]. [Pb = 207, N= 14, O = 16]

Exercise | Q 5 | Page 116

The usefulness of a fertilizer depends upon percentage of nitrogen present in it. Find which of the following is a better fertilizer:
(a) Ammonium nitrate [NH4NO3]
(b) Ammonium phosphate [(NH4)3PO4 (N=14,H=1,O=16,P=31)

Exercise | Q 6 | Page 116

A compound of lead has following percentage composition, Pb = 90.66%, O = 9.34%. Calculate empirical formula of a compound. [Pb = 207, O = 16]

Exercise | Q 7 | Page 116

Empirical formula of a compound is CH2O. If its empirical formula is equal to its vapour density, calculate the molecular formula of the compound.

Exercise | Q 8.1 | Page 116

Potassium nitrate on strong heating decomposes as under :
2KNO3 → 2KNO2 + O2
Calculate : Weight of potassium nitrite formed.
(K = 39, 0 = 16, N = 14)

Exercise | Q 8.2 | Page 116

Potassium nitrate on strong heating decomposes as under :
2KNO3 → 2KNO2 + O2
Calculate : Weight of oxygen formed when 5.05g of potassium nitrate decomposes completely.
(K = 39, 0 = 16, N = 14)

Exercise | Q 9.1 | Page 116

What is the volume occupied by 16g of sulphur dioxide. gas at STP?

Exercise | Q 9.1 | Page 116

What is the volume occupied by 48g of oxygen gas at STP?

Exercise | Q 9.2 | Page 116

Determine the  molecular mass of a gas if 5g of it occupy a volume of 4 L at STP.

Exercise | Q 10 | Page 116

What weight of sulphuric acid will be required to dissolve 3g of magnesium carbonate?
[Mg = 24, C =12, 0 = 16 ]
MgCO3 + H2SO4 → MgSO4 + H2O+ CO2

Exercise | Q 11 | Page 116

Calculate the percentage of water in ferrous sulphate crystals.
[Fe = 56, S = 32, O =16, H = 1].

Exercise | Q 12 | Page 116

An organic compound has the following percentage composition: C = 12.76%, H = 2.13%, Br = 85.11%. The vapour density of the compound is 94. Find out its molecular formula.

Exercise | Q 13 | Page 116

Two oxides of a metal (M) have 20.12% and 11.19% oxygen. The formula of the first oxide is MO. Determine the formula of the second oxide.

Exercise | Q 14 | Page 116

Calculate the volume of air at STP, required to convert 300 mL of sulphur dioxide to sulphur trioxide. Air contains 21% of oxygen by volume.

Exercise | Q 15 | Page 116

10g of NaCl solution is mixed with 17g of silver nitrate solution. Calculate the weight of silver chloride precipitated.
AgNO3 + NaCl → AgCI + NaNO3

Exercise | Q 16 | Page 116

A student puts his signature with graphite pencil. If the mass of carbon in the signature is 10-12 g. Calculate the number of carbon atoms in the signature.

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 117]

Exercise | Q 1 | Page 117

Under the same conditions of temperature and pressure you collect 2L of carbon dioxide, 3L of chlorine, 5L of hydrogen, 4L of nitrogen and 1L of sulphur dioxide. In which gas sample will there be :
a. The greatest number of molecules.
b. The least number of molecules.

Exercise | Q 2.1 | Page 117

What volume of hydrogen sulphide at STP will burn in oxygen to yield 12.8g suIphurdioxide according to the equation?
2H2S + 3O2 → 2H2O + 2SO2

Exercise | Q 2.2 | Page 117

What volume of hydrogen sulphide at STP will burn in oxygen to yield 12.8g what volume of oxygen would be required for complete combustion?

Exercise | Q 3 | Page 117

Find the total percentage of oxygen in magnesium nitrate crystal Mg(NO3)2.6H2O.
[H = 1, N = 14, O = 16, Mg = 24]

Exercise | Q 4 | Page 117

A compound contains 87.5% by mass of nitrogen and 12.5% by mass of hydrogen. Determine the empirical formula of this compound.

Exercise | Q 5.1 | Page 117

Is it possible to change the temperature and pressure of a fixed mass of a gas without changing its volume? Explain your answer.

Exercise | Q 5.2 | Page 117

Define or explain the meaning of term 'molar volume'.

Exercise | Q 6 | Page 117

What is the mass of nitrogen in 1000Kg of urea [CO(NH2)2] ?
[H = 1, C= 12, N= 14, O = 16]

Exercise | Q 7.1 | Page 117

Calculate the empirical formula of the compound having 37.6% sodium, 23.1% silicon and 39.3% oxygen.(Answer correct to two decimal places) (O = 16, Na = 23, Si = 28)

Exercise | Q 8 | Page 117

(NH4)2Cr2O7 → N2 + Cr2O3 +4H2O.
What volume of nitrogen at STP, will be evolved when 63g of ammonium dichromate is decomposed?
(H= 1, N = 14, 0 = 16, Cr = 52)

Exercise | Q 9.1 | Page 117

Calculate the percentage of boron (B) in borax (Na2B4O7.10H2O). [H = 1, B = 11, O = 16, Na = 23],
answer correct to 1 decimal place.

Exercise | Q 9.2 | Page 117

The compound A has the following percentage composition by mass: C =26.7%, O = 71.1%, H = 2.2%.
Determine the empirical formula of A.(Answer to one decimal place)  (H=1,C=12,O=16)

Exercise | Q 9.2 | Page 117

If the relative molecular mass of A is 90, what is the molecular formula of A?

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 118]

Exercise | Q 1.1 | Page 118

Water can split into hydrogen and oxygen under suitable conditions. The equations representing the change is:  2H2O(I) → 2H2 (g) + O2(g)
If a given experiment results in 2500cm3 of hydrogen being produced, what volume of oxygen is liberated at the same time under the same conditions of temperature and pressure?

Exercise | Q 1.2 | Page 118

Water can split into hydrogen and oxygen under suitable conditions. The equations representing the change is:  2H2O(I) → 2H2 (g) + O2(g)
Ammonia burns in oxygen and the combustion in the presence of a catalyst may be represented as:
2NH3 (g) +21/2O2 (g) → 2NO (g) + 3H2O (I)
What mass of steam is produced when 1.5 g of nitrogen monoxide is formed?

Exercise | Q 2.1 | Page 118

Concentrated nitric acid oxidizes phosphorous to phosphoric acid according to the following equation :
P + 5HNO3 → H3PO4 + H2O + 5NO2
What mass of nitric acid will be consumed at the same time?

Exercise | Q 2.1 | Page 118

Concentrated nitric acid oxidizes phosphorous to phosphoric acid according to the following equation :
P + 5HNO3 → H3PO4 + H2O + 5NO2
What mass of phosphoric acid can be prepared from 6 .2 g of phosphorous?

Exercise | Q 2.1 | Page 118

Concentrated nitric acid oxidizes phosphorous to phosphoric acid according to the following equation :
P + 5HNO3 → H3PO4 + H2O + 5NO2
What will be the volume of steam at the same time measured at 760mm of Hg pressure and 273°C? [H=1, N=14, O=16, P=31]

Exercise | Q 2.2 | Page 118

Ammonia may be oxidized to ni trogen monoxide in the presence of a catalyst according to th e equation as:
4NH3 + 5O2 → 4NO + 6H2O
If 27L of reactants are consumed, what volume of ni trogen monoxide is produced at the same temperature and pressure?

Exercise | Q 3 | Page 118

If a crop of wheat removes 20 Kg of nitrogen per hectare of soil, what mass of the fertilizer calcium nitrate,Ca(NO3)2 would be required to replace nitrogen in 10 hectare field? (N = 14, O = 16, Ca = 40)

Exercise | Q 4.1 | Page 118

A vessel contains N molecules of oxygen at a certain temperature and pressure. How many molecules of sulphur dioxide can the vessel accommodate at the same temperature and pressure?

Exercise | Q 4.2 | Page 118

If the hydrogen sample contains N molecules, how many molecules are present in oxygen sample?

Exercise | Q 4.2 | Page 118

Each of the two flasks contains 2.0 g of gas at the same temperature and pressure. One flask contains oxygen and the other hydrogen. Which sample contains the greater number of molecules?

Exercise | Q 5.1 | Page 118

If 112 cm3 of hydrogen sulphide is mixed with 120 cm3 of chlorine at STP, what is the mass of sulphur formed?
H2S + Cl2 → 2HCI + S

Exercise | Q 5.2 | Page 118

Washing soda has the formula Na2CO3.10H2O.What is the mass of anhydrous sodium carbonate left when all the water of crystallization is expelled by heating 57.2 g of washing soda?

Exercise | Q 5.3 | Page 118

When excess lead nitrate solution was added to a solution of sodium sulphate, 15.1g of lead sulphate was precipitated. What mass of sodium sulphate was present in the original solution?
Na2SO4 + Pb(NO3)2 → PbSO4 + 2NaNO3
(H = 1, C = 12, O = 16, Na = 23, S = 32, Pb = 207)

Exercise | Q 6 | Page 118

Determine the empirical formula of the compound whose composition by mass is 42% nitrogen, 48% oxygen and 9% hydrogen.[N=14,O=16,H=1]

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 119]

Exercise | Q 1 | Page 119

When gases react their volumes bear a simple ratio to each other, under the same conditions of temperature and pressure. Who proposed this gas law?

Exercise | Q 2 | Page 119

What volume of oxygen would be required for complete combustion of 100L of ethane according to the following equation?
2C2H6 + 7O2 → 4CO2 + 6H2O

Exercise | Q 3 | Page 119

Chlorine, nitrogen, ammonia and sulphur dioxide gases are collected under the same conditions of temperature and pressure.
Copy the following table which gives the volumes of the gases collected, and the number of molecules (X) in 20L of nitrogen.You are to complete the table by giving the number of molecules in th e other gases, in terms of X.

 Gas Volume(litres) Number of molecules Chlorine 10 Nitrogen 20 X Ammonia 20 Sulphur dioxide 5
Exercise | Q 4 | Page 119

Mention the term defined by the following sentence:
The mass of a given volume of gas compared to the mass of an equal volume of hydrogen.

Exercise | Q 5 | Page 119

The reaction 4N2O + CH4 → CO2 + 2H2O + 4N2 takes place in the gaseous state. If the volumes of all the gases are measured at the same temperature, and pressure, calculate the volume of dinitrogen oxide (N2O), required to give 150cm3 of steam.

Exercise | Q 6 | Page 119

Calculate the percentage of phosphorous in the fertilizer superphosphate, Ca(H2PO4)2. [Ca = 40, H =1, P =31, O = 16] (Correct to 1 decimal place)

Exercise | Q 7 | Page 119

A metal M, forms a volatile chloride containing 65.5% Chlorine. If the density of the chloride relative to hydrogen is 162.5, find the molecular formula of the chloride. [M = 56, Cl = 35.5]

Exercise | Q 8.1 | Page 119

Samples of the gases O2, N2, CO2 and CO under the same conditions of temperature and pressure contain the same number of molecules represented by X. The molecules of Oxygen, occupy V litres and have a mass of 8 g. Under the same conditions of temperature and pressure :
What is the volume occupied by : X molecules of N2.

Exercise | Q 8.1 | Page 119

Samples of the gases O2, N2, CO2 and CO under the same conditions of temperature and pressure contain the same number of molecules represented by X. The molecules of Oxygen, occupy V litres and have a mass of 8 g. Under the same conditions of temperature and pressure :
What is the volume occupied by : 3X molecules of CO? [C=12,N=14,O=16]

Exercise | Q 8.2 | Page 119

Samples of the gases O2, N2, CO2 and CO under the same conditions of temperature and pressure contain the same number of molecules represented by X. The molecules of Oxygen, occupy V litres and have a mass of 8 g. Under the same conditions of temperature and pressure :
What is the mass of CO2 in g?

Exercise | Q 8.3 | Page 119

Samples of the gases O2, N2, CO2 and CO under the same conditions of temperature and pressure contain the same number of molecules represented by X. The molecules of Oxygen, occupy V litres and have a mass of 8 g. Under the same conditions of temperature and pressure:
In answering the above questions, which law have you used?

Exercise | Q 9 | Page 119

Calculate the percentage of platinum in ammonium chloroplatinate (NH4)2PtCl6.
[N = 14, H = 1, Pt = 195, Cl =35.5]

Exercise | Q 10 | Page 119

The percentage composition of sodium phosphate, as determined by analysis is : 42.1% Na, 18.9% P, 39% of O. Find the empirical formula of the compound.
[H =1, N =14, Na = 23, P = 31, Cl = 35.5, Pt = 195]

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 120]

Exercise | Q 1.1 | Page 120

What volume of oxygen is required to burn completely a mixture of 22.4 dm3 of methane and 11 .2 dm3 of hydrogen in to carbon dioxide and steam? Equations of the reactions are given below:
CH4 + 2O2 → CO2 + 2H2O
2H2 + O2 → 2H2O

Exercise | Q 1.2 | Page 120

The gases hydrogen, oxygen, carbon dioxide, sulphur dioxide and chlorine are arranged in order of their increasing relative molecular mass. Given 8 g of each gas at STP, which gas will contain the least number of molecules and which gas the
most?

Exercise | Q 2.1 | Page 120

A flask contains 3.2g of sulphur dioxide.Calculate the following : The moles of sulphur dioxide present in the flask.

Exercise | Q 2.1 | Page 120

A flask contains 3.2g of sulphur dioxide. Calculate the following : The volume occupied by 3.2g of sulphur dioxide at STP.

Exercise | Q 2.1 | Page 120

A flask contains 3.2g of sulphur dioxide. Calculate the following: The number of molecules of sulphur dioxide present in the flask.

Exercise | Q 2.2 | Page 120

The reaction of potassium permanganate (VII) with acidified iron (II) sulphate is given below:
2KMno4 + 10FeSO4 + 8H2O → K2SO4 + 2MnSO4 + 5Fe2(SO4)3 + 8H2O
If 15.8g of potassium permanganate (VII) was used in the reaction, calculate the mass of iron (II) sulphate used in the above reaction.

Exercise | Q 3.1 | Page 120

When heated, potassium permanganate decomposes according to the following equation :
2KMnO4 → K2MnO4 + MnO2 + O2
Some potassium permanganate was heated in test tube. After collecting one litre of oxygen at room temperature, it was found that the test tube had undergone a loss in mass of 1.32g . If one litre of hydrogen under the same conditions of temperature and pressure has a mass of 0.0825g, calculate the relative molecular mass of oxygen.

Exercise | Q 3.2 | Page 120

When heated, potassium permanganate decomposes according to the following equation :
2KMnO4 → K2MnO4 + MnO2 + O2
Given that the molecular mass of potassium permanganate is 158g, what volume of oxygen (measured at room temperature) would be obtained by the complete decomposi tion of 15.8g of potassium permanganate?
(Molar volume at room temperature is 24 litres). [K = 39, Mn = 55, 0 = 16 ]

Exercise | Q 4.1 | Page 120

The equations given below relate to the manufacture of sodium carbonate (Molecular weight of Na2CO3 = 106).
NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl

2NaHCO3 → Na2CO3 + H2O + CO2
What mass of sodium hydrogen carbonate must be heated to give 21.2g of sodium carbonate? based on the production of 21.2g of sodium carbonate.

Exercise | Q 4.2 | Page 120

The equations given below relate to the manufacture of sodium carbonate (Molecular weight of Na2CO3 = 106).
NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl

2NaHCO3 → Na2CO3 + H2O + CO2
To produce the mass of sodium hydrogen carbonate what volume of carbon dioxide, measured at STP would be required?based on the production of 21.2 g of sodium carbonate.

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 121]

Exercise | Q 1.1 | Page 121

The volumes of gases A, B, C and D are in the ratio, 1:2:2:4 under the same conditions of temperature and pressure.
If the volume of A is actually 5.6 dm3 at STP, calculate the number of molecules in the actual volume of D at STP.

Exercise | Q 1.1 | Page 121

The volumes of gases A, B, C and D are in the ratio, 1:2:2:4 under the same conditions of temperature and pressure.
The number of molecules in the actual volume of D at STP is 6 x 1023 molecules. state, the mass of D if the gas is dinitrogen oxide (N2O)

Exercise | Q 1.1 | Page 121

The volumes of gases A, B, C and D are in the ratio, 1:2:2:4 under the same conditions of temperature and pressure.
Which sample of gas contains the maximum number of molecules?

Exercise | Q 1.1 | Page 121

The volumes of gases A, B, C and D are in the ratio, 1:2:2:4 under the same conditions of temperature and pressure.
If the temperature and the pressure of gas A are kept constant then what will happen to the volume of A when the number of molecules is doubled?

Exercise | Q 1.1 | Page 121

The volumes of gases A, B, C and D are in the ratio, 1:2:2:4 under the same conditions of temperature and pressure.
If this ratio of gas volumes refers to the reactants and products of a reaction, which gas law is being observed?

Exercise | Q 1.2 | Page 121

Calculate the percentage of nitrogen in aluminium nitride. [Al = 27, N = 14]

Exercise | Q 2.1 | Page 121

Determine the empirical formula of a compound containing 47.9‰ K, 5.5‰ beryllium and 46.6‰ fluorine by mass.

Exercise | Q 2.2 | Page 121

Given that the relative molecular mass of copper oxide is 80, what volume of ammonia (measured at STP) is required to completely reduce 120g of copper oxide? The equation for the reaction is :
3CuO + 2NH→ 3Cu + 3H2O + N2

Exercise | Q 3.1 | Page 121

Calculate the number of moles and number of molecules present in 1.4 g of ethylene gas. What is the volume occupied by the same amount of ethylene?

Exercise | Q 3.2 | Page 121

What is the vapour density of ethylene? (Avogadro's number = 6 x 1023; Atomic weight of C = 12, H = 1; Molar volume = 22.4 litres at STP)

Exercise | Q 4.1 | Page 121

Calculate the percentage of sodium in sodium aluminium fluoride (Na3AIF6).
[F = 19, Na = 23, Al = 27]

Exercise | Q 4.2 | Page 121

560ml of carbon monoxide is mixed with 500ml of oxygen and ignited. The chemicaI equation for the reaction is as folIows:
2CO + O2 → 2CO2
Calculate the volume of oxygen used and carbon dioxide formed in the above reaction.

Exercise | Q 5.1 | Page 121

A sample of ammonium nitrate when heated yields 8.96 litres of steam (measured at STP)
NH4NO3 → N2O + 2H2O
What volume of dinitrogen oxide is produced at the same time as 8.96 L of steam?

Exercise | Q 5.2 | Page 121

A sample of ammonium nitrate when heated yields 8.96 litres of steam (measured at STP)
NH4NO3 → N2O + 2H2O
What mass of ammonium nitrate should be heated to produce 8.96L of steam?

Exercise | Q 5.3 | Page 121

A sample of ammonium nitrate when heated yields 8.96 litres of steam (measured at STP)
NH4NO3 → N2O + 2H2O
Determine the percentage of oxygen in the ammonium nitrate?

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 122]

Exercise | Q 1.1 | Page 122

A compound 'X' consists of 4.8% of C and 95.2% of Br by mass.
Determine the empirical formula of this compound.
[C = 12, Br = 80]

Exercise | Q 1.2 | Page 122

A compound 'X' consists of 4.8% of C and 95.2% of Br by mass.
If the vapour density of the compound is 252, what is the molecular formula of the compound?

Exercise | Q 1.3 | Page 122

A compound 'X' consists of 4.8% of C and 95.2% of Br by mass.
Name the type of chemical reaction by which X can be prepared from ethane.

Exercise | Q 2 | Page 122

Choose the correct alternative :
The gas laws which relates the volume of a gas to the number of molecules of the gas is :

• Gay-Lussac's law

• Boyle's law

• Charle's law

Exercise | Q 3.1 | Page 122

The equation for the burning of octane is :
2C8H18 + 25O→ 16CO2 + 18H2O
How many moles of carbon dioxide are produced when one mole of octane burns ?

Exercise | Q 3.2 | Page 122

The equation for the burning of octane is :
2C8H18 + 25O2 → 16CO2 + 18H2O
What volume, at STP, is occupied by 8 moles ?

Exercise | Q 3.3 | Page 122

The equation for the burning of octane is :
2C8H18 + 25O→ 16CO2 + 18H2O
If the relative molecular mass of carbon dioxide is 44, what is the mass of carbon dioxide produced by burning two moles of octane?

Exercise | Q 3.5 | Page 122

What is the empirical formula of octane?

Exercise | Q 4.1 | Page 122

(i) A compound has the following percentage composition by mass : C is 14.4‰, H is 1.2‰ and Cl is 84.5‰
Determine the empirical formula of this compound.
(ii ) The relative molecular mass of this compound is 168, so what is its molecular formula?
(iii ) By what type of reaction could this compound be obtained from ethylene?

Exercise | Q 4.2 | Page 122

From the equation :
C + 2H2SO4 → CO2 + 2H2O + 2SO2
Calculate:
(i) The mass of carbon oxidized by 49g of sulphuric acid (C = 12, relative molecular mass of sulphuric acid = 98)
(ii ) The volume of sulphur dioxide measured at STP, liberated at the same time.

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 123]

Exercise | Q 1 | Page 123

A gas cylinder of capacity of 20dm3 is filled with gas X the mass of which is 10g. When the same cylinder is filled with hydrogen gas at the same temperature and pressure the mass of the hydrogen is 2g, hence the relative molecular mass of the gas is :

• 5

• 10

• 15

• 20

Exercise | Q 2.1 | Page 123

Calcium carbide is used for the artificial ripening of fruits. Actually the fruit ripens because of the heat evolved while calcium carbide reacts with the moisture. During this reaction calcium hydroxide and acetylene gas is formed.
If 200cm3 of acetylene is formed from a certain mass of calcium carbide, find the volume of oxygen required and carbon dioxide formed during the complete combustion . The combustion reaction can be represented as below:
2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g).

Exercise | Q 2.2 | Page 123

A gaseous compound of nitrogen and hydrogen contains 12.5‰  hydrogen by mass. Find the molecular formula of the compound if its relative molecular mass is 37.

Exercise | Q 3 | Page 123

Correct the following statement :
Equal masses of all gases under identical conditions contain the same number of molecules.

Exercise | Q 3.2 | Page 123

Commercial sodium hydroxide weighing 30g has some sodium chloride in it. The mixture on dissolving in water and subsequent treatment with excess silver nitrate solution formed a precipitate weighing 14.3g. What is the percentage of sodium chloride in the commercial sample of sodium hydroxide? The equation for the reaction is:
NaCl + AgNO3 → AgCI + NaNO3
[Relative molecular mass = 58, AgCI = 143]

Exercise | Q 4.1 | Page 123

A gas cylinder contains 24 x 1024 molecules of nitrogen gas. If Avogadro's number is 6 x 1023 and the relative atomic mass of nitrogen is 14,
Calculate : Volume of nitrogen at STP in dm3.

Exercise | Q 4.1 | Page 123

A gas cylinder contains 24 x 1024 molecules of nitrogen gas. If Avogadro's number is 6 x 1023 and the relative atomic mass of nitrogen is 14,
Calculate : Mass of nitrogen gas in the cylinder.

Exercise | Q 4.3 | Page 123

A certain gas 'X' occupies a volume of 100 cm3 at STP and weights 0.5g. Find its relative molecular mass.

Exercise | Q 5.1 | Page 123

LPG stands for liquefied petroleum gas. Varieties of LPG are marketed including a mixture of propane (60%) and butane (40%). If 10 litre of this mixture is burnt, find the total volume of carbon dioxide gas added to the atmosphere. Combustion reaction can be presented as :
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)

Exercise | Q 5.2 | Page 123

Calculate the percentage of nitrogen and oxygen in ammonium nitrate.[Relative molecular mass of ammonium nitrate is 80, H=1, N=14, O = 16].

Exercise | Q 6.1 | Page 123

4.5 moles of calcium carbonate are reacted with dilute hydrochloric acid.Write the equation for the reaction.

Exercise | Q 6.2 | Page 123

4.5 moles of calcium carbonate are reacted with dilute hydrochloric acid.What is the mass of 4.5 moles of calcium carbonate? Relative molecular mass of calcium carbonate is 100)

Exercise | Q 6.3 | Page 123

4.5 moles of calcium carbonate are reacted with dilute hydrochloric acid. What is the volume of carbon dioxide liberated at STP?

Exercise | Q 6.4 | Page 123

4.5 moles of calcium carbonate are reacted with dilute hydrochloric acid. What mass of calcium chloride is formed? (Relative molecular mass of calcium chloride is 111)

Exercise | Q 6.5 | Page 123

4.5 moles of calcium carbonate are reacted with dilute hydrochloric acid.How many moles of HCl are used in this reaction

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 124]

Exercise | Q 1.1 | Page 124

Calculate the volume of 320g of SO2 at STP .
(Atomic mass : S = 32 and O = 16)

Exercise | Q 1.2 | Page 124

State Gay-Lussac's Law of combining volumes.

Exercise | Q 1.3 | Page 124

Calculate the volume of oxygen required for the complete combustion of 8.8 of propane (C3H5).
(Atomic mass : C = 14, O = 16, H = 1, Molar Volume = 22.4 dm3 at STP)

Exercise | Q 2 | Page 124

An organic compound with vapour density = 94 contains C = 12.67%, H = 2.13% and Br = 85.11%. Find the molecule formula.
[Atomic mass C = 12, H = 1, Br = 80]

Exercise | Q 3.1 | Page 124

Calculate the mass of : 1022 atoms of sulphur
[Atomic mass : S = 32,C=12, and O = 16 and Avogadro's number = 6 × 1023]

Exercise | Q 3.2 | Page 124

Calculate the mass of : 0.1 mole of carbon dioxide
[Atomic mass : S = 32,C=12, and O = 16 and Avogadro's number = 6 × 1023]

Exercise | Q 4.1 | Page 124

O2 is evolved by heating KCIO3 using MnO2 as a catalyst.
$\ce{2KCI3 ->[Mno2] 2KCl + 3O2}$
(i) Calculate the mass of KClO3 required to produce 6.72 litre of O2 at STP.
(ii) Calculate the number of moles of oxygen present in the above volume and also the number of molecules
(iii) Calculate the volume occupied by 0.01 mole of CO2at STP

Exercise | Q 5.1 | Page 124

Solve the following :
What volume of oxygen is required to burn completely 90dm3 of butane under similar conditions of temperature and pressure?
2C4H15 + 13O2 → 8CO2 + 10H2O

Exercise | Q 5.2 | Page 124

Solve the following :
The vapour density of a gas is 8. What would be the volume occupied by 24.0 of the gas at STP?

Exercise | Q 5.3 | Page 124

Solve the following :
A vessel contains X number of molecules of hydrogen gas at a certain temperature and pressure. How many molecules of nitrogen gas would be present in the same vessel under the same conditions of temperature and pressure?

Exercise | Q 6.1 | Page 124

Oxygen oxidase ethyne to carbon dioxide and water as shown by the equation :
2C2H+ 5O→ 4CO+ 2H2O
What volume of ethylene gas at STP is required to produce 8.4 dm3 of carbon dioxide at STP?

Exercise | Q 6.2 | Page 124

A compound made up of two elements X and Y has an empirical formula X2Y. if the atomic weight of X is 10 and that Y is 5 and the compound has a vapour density 25, find its molecular formula.

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 125]

Exercise | Q 1.1 | Page 125

Give one word or phrase for the following :
The ratio of the mass of a certain volume of gas to the mass of an equal volume of hydrogen under the same conditions of temperature and pressure.

Exercise | Q 1.2 | Page 125

Give one word or phrase for the following:
Formation of ions from molecules.

Exercise | Q 2.1 | Page 125

Exercise | Q 2.2 | Page 125

A cylinder contains 68g of ammonia gas at STP
(1) What is the volume occupied by this gas?
(2) How many moles of ammonia are present in the cylinder?
(3) How many molecules of ammonia are present in the cylinder? [N-14,H-1]

Exercise | Q 3 | Page 125

Which of the following would weight the least?
[Atomic masses : Ag = 108, N - 14, O = 16,C = 12]

• 2 gram atoms of Nitrogen

• 1 mole of Silver

• 22.4 litres of oxygen gas at 1 atmospheric pressure and 273K

• 6.02 × 1023 atoms of carbon

Exercise | Q 4.1 | Page 125

Complete the following calculations. Show working for complete credit :
Calculate the mass of calcium that will contain the same number of atoms as are present in 3.2 gm of Sulphur. [Atomic masses : S = 32, Ca = 40]

Exercise | Q 4.2 | Page 125

Complete the following calculations. Show working for complete credit :
If 6 litres of hydrogen and 4 litres of chlorine are mixed and exploded and if water is added to the gases formed, find the volume of the residual gas.

Exercise | Q 4.3 | Page 125

Complete the following calculations. Show working for complete credit :
If the empirical formula of a compound is CH and it has a vapour density of 13, find the molecular formula of the compound.

Exercise | Q 5 | Page 125

Consider the following reaction and based on the reaction answer the questions that follow :
$\ce{(NH4)2Cr2O7 ->[heat] N2(g) + 4H2O(g) + Cr2O3}$
Calculate :
(i) The quantity in moles of (NH4)2Cr2O7 if 63 gm of (NH4)2Cr2O7 is heated.
(ii) The quantity in moles of nitrogen formed.
(iii) The volume in litres or dm3 of N2evolved at STP.
(iv) The mass in grams of Cr2O3 formed at the same time
[Atomic masses : H = 1, Cr=52, N=14]

Exercise | Q 6 | Page 125

A gas cylinder contain 12 × 1024 molecules of oxygen gas
If Avogadro's number is 6 × 1023,
calculate :
(i) The mass of oxygen present in the cylinder.
(ii) The volume of oxygen at STP present in the Cylinder[O=16]

Exercise | Q 7 | Page 125

A gaseous hydrocarbon contains 82.76% of carbon. Given that its vapour density is 29, find its molecular formula.
[C = 12, H = 1]

#### Chapter 5: Mole Concept And Stoichiometry Exercise Exercise solutions [Page 126]

Exercise | Q 1 | Page 126

The equation 4NH35O→ 4NO + 6H2O represents the catalytic oxidation of ammonia. If 100 cm3of ammonia is used, calculate the volume of oxygen required to oxidise the ammonia completely.

Exercise | Q 2 | Page 126

A gas of 32 g mass has a volume of 20 litres at STP. Calculate the gram molecular weight of the gas.

Exercise | Q 3 | Page 126

How much calcium oxide is formed when 82g of calcium nitrate is heated? Also find the volume of nitrogen dioxide evolved:
2Ca(NO3)2→ 2CaO + 4NO2 + O2 (Ca = 40,N = 14, O = 16)

Exercise | Q 4 | Page 126

The ratio between the number of molecules in 2g of hydrogen and 32 g of oxygen is
[Given that H=1,O=16]

• 1:2

• 1:0:01

• 1:1

• 0.01:1

Exercise | Q 5.1 | Page 126

Calculate the number of gram atoms in 4.6 grams of sodium (Na = 23)

Exercise | Q 5.2 | Page 126

Calculate the percentage of water of crystallization in CuSO4. 5H2O
(H = 1, O = 16, S = 32, Cu = 64)

Exercise | Q 5.3 | Page 126

A compound of X and Y has the empirical formula XY2. Its vapour density is equal to its empirical formula weight. Determine its molecular formula.

Exercise | Q 6.1 | Page 126

Propane burns in air according to the following equation :
C3H+ 5O→ 3CO2 + 4H2O
What volume of propane is consumed on using 1000 cm3of air, considering only 20% of air contains oxygen?

Exercise | Q 6.2 | Page 126

The mass of 11.2 litres of a certain gas at s.t.p is 24 g. Find gram molecular mass of the gas

Exercise | Q 7 | Page 126

A gas cylinder can hold 1 kg of hydrogen at room temperature and pressure.
(a) Find the number of moles of hydrogen present
(b) What weight of CO2can the cylinder hold under similar conditions of temperature and pressure? (H = 1 C = 12, O = 16)
(c) If the number of molecules of hydrogen in the cylinder is X, calculate the number of CO2 molecules in the cylinder with the same conditions of temperature and pressure.
(d) State the law that helped you to arrive at the above result.

Exercise

## Frank solutions for Class 10 Chemistry chapter 5 - Mole Concept And Stoichiometry

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