Basics of Mole Concept

Basics

O f

BASICS OF MOLE CONCEPT - Parishkrit Jain

1

Let us try to understand the mole concept with a simple example:

If you have ever visited in a bank then you might have observed that people working

there have large number of coins of various denominations. As you can imagine, it

would really be very tedious to count such large number of coins. Then how do these

people count them? Well, the simple method is to weigh the coins. Sounds strange! But

it is true. Think of simpler example related to your life. We use to have grains (wheat,

rice, etc.) or sugar in our houses. Do we really count each and every grain or sugar

particle? Surely no. We just weigh them. It is often convenient to do so, especially in the

case of grains and sugar. Let us go back to our example of banks. A simple question may

arise in your mind: Knowing the weight of some coins of given denomination how can

be count the total number of coins? The method is indeed very interesting and requires

some simple math. You know that a fixed number of coins (of same denomination) will

have the same mass. Let us, for an example, think that 10, ₹ 5 coins weigh 50 grams

then you can know the weight of a single coin easily. Yes, it would be 5 grams. Now they

put some coins on a weighing machine which shows their weight to be 550 grams. Can

you figure out the number of coins on the weighing machine? We have the following

relation:

Weight of 1 coin = 5 grams.

Let, Weight of coins = 550 grams

Therefore, =

= 110 coins

So, Number of coins = 110

This was rather simple but using this simple concept scientists count the ‘number’ of

atoms or molecules present in elements and compounds (i.e. from their mass). In fact

this ‘number’ is referred to as mole. But a simple question may arise in your mind:

What is the need of counting the number of atom or molecules?

Well, let us answer this question for you. Consider a simple chemical reaction, involved

in formation of water:

2H2 + O2 → 2H2O


2

You can observe from this equation that in a chemical equation the number of

molecules or atoms taking part in the reaction is indicated. Here, 2 molecules of

Hydrogen combine with a single molecule of Oxygen to form 2 molecules of water. Thus,

a chemical reaction directly indicates the number of atoms taking part in the reaction.

So, it is more convenient to refer to the quantity of a substance in terms of the number

of atoms taking part in the reaction, rather than their masses. Chemists need the

number of atoms and molecules while carrying out reactions, and for this they need to

relate the mass in grams to the number. Thus, a mole is the chemist’s counting unit. It

has the unit symbol mol. Now let us move back to our previous discussion to see how

they relate mass in grams to the number.

How do scientists count atoms and molecules?

The answer is simple: by weighing them. Experimentally it has been found that if we

weigh an element equal to its atomic mass in grams, then it contains 6.022 X 1023 atoms

of the element. Recall that mole is actually a number. For example, 1 dozen apples

always means only and only 12 apples, irrespective of their shape and size. Similarly:

1 mole (of anything) = 6.022 X 1023 in number

1 mole of atoms = 6.022 X 1023 number of atoms

1 mole of molecules = 6.022 X 1023 number of molecules

1 mole of particles (atoms, molecules, ions) = 6.022 X 1023 number of particles

From this discussion we have the following relation:

Gram atomic mass (of anything) = 1 mole (of anything) = 6.022 X 1023 in number

You can also observe the advantage of using mole rather than dozen or gross that mass

of 1 mole of a particular substance is always fixed. It is always equal to the relative

atomic mass or molecular mass in grams.

What is this 6.022 X 1023 actually called?

This 6.022 X 1023 is actually called the Avogadro number or Avogadro constant

(represented by NA or NO) in honour of Italian scientist Amadeo Avogadro.

How do we write the gram atomic mass of an element?


3

Before moving further let us first see what is gram atomic mass or molar mass. Mass of

1 mole of particles is called molar mass or gram atomic mass. To get it, we take the

numerical value of the atomic mass and simply write gram (g) after that or in other

words, we write the atomic mass but place ‘g’ instead of ‘u’. For example, atomic mass

of hydrogen=1u. So, gram atomic mass of hydrogen = 1g. So, can you tell now what the

gram atomic mass of Sodium is? (Remember that the atomic mass of Sodium is 23u).

Yes, it is 23g.

Now, we know that 1u of hydrogen has 1 atom of hydrogen. So, 1g of hydrogen has 1

mole of atoms that is 6.022 X 1023 atoms of Hydrogen. Let us consider one more

example. 16u oxygen has only 1 atom of oxygen, 16 g oxygen has 1 mole atoms, that is,

6.022×1023 atoms of oxygen. Before moving on, there is a question for you:

Question. What is the molar mass of water?

Solution. Molecular formula of water is H2O.

Now, Atomic mass of Hydrogen = 1u

Atomic mass of Oxygen = 16u

Therefore, Molecular mass of water = (2 X 1u) + 16u = 18u

So, Molar mass of water = 18g

What do you understand from this? 18u water has only 1 molecule of water, 18g water

has 1 mole molecules of water, that is, 6.022×1023 molecules of water.

The word “mole” was introduced around

1896 by Wilhelm Ostwald who derived

the term from the Latin word moles

meaning a „heap‟ or „pile‟. A substance

may be considered as a heap of atoms

or molecules. The unit mole was

accepted in 1967 to provide a simple

way of reporting a large number- the

massive heap of atoms and molecules in

a sample.

Wilhelm Ostwald

FACT

TO

KNOW ???


4

The illustration given below shows the relationship between mole, Avogadro number

and mass:

Let us now try to define the important terms we have learnt so far:

‘Mole is the amount of substance that contains the same number of particles.’

‘1 mole of any species (atoms/molecules/ions/particles) is that quantity in number

having a mass equal to its atomic mass or molecular mass in grams.’

We can define Avogadro constant 6.022X1023 as ‘the number of atoms in exactly 12

grams of Carbon-12.’


5

Solving Problems Related To Mole Concept. Before moving further we need to know the following symbols used while solving

numerical problems: Number of moles = n

Given mass = m

Molar mass = M

Given number of particles = N

Avogadro number = NO

Let us now suppose that we need to find number of moles (i.e. n) in a given mass (m) of

element x, given that the molar mass of the element is M.

Now, Molar mass of x = 1 mole of element x

So,

=

Or, =

In other words, =

Let us understand this relation with a simple example:

Sample Problem 1. Calculate the number of mole in 52 g of Helium.

Solution. We know that, Atomic mass of He = 4u

So, its molar mass = 4 g

That is, 4 g of He contains 1 mole of He.

Or, 4 g of He = 1 mole of He

So, 52 grams of Helium =

X 52 mole

= 13 moles

Therefore, there are 13 moles in 52 g of He.

KEY CONCEPT


6

From the 5th step of this example you could have easily observed that 52 grams (i.e.

given mass) of Helium contains

number of moles. Thus, we verify

our relationship.

Now, Let us try to find number of moles (i.e. n) for given number of particles (N) of an

element x.

We know that, 1 mole (of anything) = 6.022 X 1023 in number

i.e., 1 mole of x = NO

=>

=

=> =

In other words, =

Now let us look at some sample problems to illustrate the use of above formulas.

Sample Problem 2. Calculate the number of moles for 12.044 X 1023 atoms of Helium.

Solution. We know that,

=

Or, =

=

= 2

Therefore, there are 2 moles in 12.044 X 1023 atoms of He.

Before moving further we have got a simple exercise for you to let you apply the

concepts you have learned so far.

KEY CONCEPT


7

WHAT HAVE YOU LEARNT?

1. In 1896, William Ostwald, introduced a term mole which

can be defined as…………………………...........……………..………………

………………………………………………………………………………………………

………………………………………………………………………………………………

2. What do the following symbols mean?

n ……………………………………………………

N …………………………………………………..

M ………………………………………………….

M ………………………………………………….

3. The Avogadro constant is ………………………………….. and is

represented as …………

4. How many moles are there in 5 grams of calcium?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………


8

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

5. How many moles there in 12.044 X 1023 atoms of phosphorous?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………


9

So, far we have learned the following important relations:

=

and, =

So, we can now easily find the number of moles in a given mass of element or given

number of particles. But have you ever thought how can we find the mass of an element

or the number of particles of an element that contains given number of moles?

That’s rather simple! In fact, we can do so and many other related things using just

these basic key concepts. Let us do so.

Suppose we need to find mass of an element x that contains given mole of atoms.

We know that, =

Or, =

Or,

Or, Mass = Number of moles X Molar mass.

Let us now suppose that we need to find number of particles (N) of an element in a

given mole of atoms.

We know that,

=

Or, =

Or,

Or, Number of particles = Number of moles X Avogadro number.

Can you find the mass (m) of an element if the number of particles (N) is known? Or, can

you find the number of particles (N) in a given mass (m) of an element?


10

Let us now suppose that we need to determine mass (m) of an element when the

number of particles (N) is known.

We have, =

Or, =

………...……………… (i)

We also know that, Mass = Number of moles X Molar mass.

Or, m = M X n

Substituting for n from (i),

We get, m = M X

... Mass =

Let us now suppose that we need to determine the number of atoms (N) in a given mass

(m) of an element.

We have, =

Or, =

………...……………… (i)

We also know that, Number of particles = Number of moles X Avogadro number.

Or,

Substituting for n from (i),

We get, N =

... Number of particles =


11

So, we a seen a lot many number of derivations from two simple key formulas. Let us

now look at all of them for once.

a) Mass = Number of moles X Molar mass

b) Number of particles = Number of moles X Avogadro number

c) Mass =

d) Number of particles =

The following sample problems illustrate the use of all these formulas.

Sample Problem 3. Calculate the mass of 0.5 mole of Nitrogen atoms.


Mass = Number of moles X Molar mass

Or,

= 0.5 X 14

= 7 g

Therefore, mass of 0.5 mole of N atoms is 7 grams.

Sample Problem 4. What is the mass of 3.011 X 1023 number of Nitrogen atoms?


Mass =

Or, m = M X

= 14 X

= 7 g

Therefore, mass of 3.011 X 1023 number of N atoms is 7 grams.


12

Sample Problem 5. Calculate the number of particles in each of the following:

(i) 0.1 mole of Carbon atoms (ii) 46 grams of Sodium atoms.

Solution. (i) We know that,

Number of particles = Number of moles X Avogadro number

Or,

= 0.1 X 6.022 x 1023

= 6.022 X 1022

Therefore, 0.1 mole of C atoms have 6.022 X 1022 number of atoms.

(ii) We know that,

Number of particles =

Or, N =

= X

= 12.044 X 1023

Therefore, 46 g of Na atoms have 12.044 X 1023 number of atoms.

Thus we see the application of concepts we have learned in the chapter. Now we have

got some exercises for you to work on and learn the things with ease. But before that,

let us revise the key formulas once again:

=

and, =


13

WHAT HAVE YOU LEARNT?

1. One mole of any species is that quantity in number

………………………….…………………………...........……………..………………

………………………………………………………………………………………………

………………………………………………………………………………………………

2. State the formulas to find the number of atoms in a given mole and in a given mass of elements.

Formula 1 ……………………………………………………….....…………………

……………………………………………………….....………………………………….

Formula 2…………………………………….…………………………………………

………….....……………………………..………………………………………………..

3. What is the mass of 4 moles of Aluminum atoms?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………


14

4. Determine the number of iron atoms in a piece of iron weighing 2.8 grams.

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

5. If one mole of Carbon atoms weigh 12 grams, what is mass in grams of a single atom of Carbon?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

…………………………………………………………………………….…………………


15

Here we go looking at some more sample questions to get a better understanding of the

text.

Sample Problem 6. Calculate the mass of 0.5 mole of N2 gas.


Mass = Number of moles X Molar mass

Or,

= 0.5 X (14+14)

= 14 g

Therefore, mass of 0.5 mole of N2 atoms is 14 grams.

Sample Problem 7. Convert 12.044 X 1022 molecules of Sulphur dioxide into moles?


Number of moles =

Or, n =

=

= 0.2

Therefore, 12.044 X 1022 molecules of SO2 contains 0.2 mole.

Sample Problem 8. In which case the number of Hydrogen atoms is more- 2 mol of HCl or 1 mol of NH3?

Solution. We know that, HCl contains 2 moles of H atoms.

Also, NH3 contains 3 moles of H atoms.

Therefore, 1 mole of NH3 contains more number of atoms.


16

Sample Problem 9. An ornament of silver contains 20 gram silver. Calculate the moles of silver present.


=

Or, =

=

= 0.185

Therefore, there are 0.185 mol in 20 g of Ag.

Sample Problem 10. If 1 g sulphur dioxide contains x molecules, what will be the number of molecules in 1 g of methane?

Solution. We have,

1 mol of SO2 = 32 + (16 X 2)

= 64 gram

... 1 g of SO2 =

mole

Now,

mole of SO2 contains x molecules.

...

mole of methane also contain x molecules.

Now, 1 mol of CH4 = 12 + (4 X 1)

= 16 gram

... 1 g of CH4 =

mole

But

mole of methane = x molecules.

...

mole of CH4 =

molecules

= 4x molecules

... If 1 g of SO2 contains x molecules, then 1 g of CH4 contains 4x molecules.

And now the time comes for you to test yourself.


17

WHAT HAVE YOU LEARNT? 1. One mole of oxygen atoms = ………………………….…… oxygen atoms in number

2. Choose the correct option in the following: Which of the following has maximum number of molecules?

(a) 4 g of H2 gas (b) 1 mole of H2O gas

(c) 3 mole of CO (d) 22 g of CO2

3. Choose the correct option in the following: What is the number of Sulphur atoms in one mole of S8?

(a) 4.818 X 1024 (b) 4.121 X 1024

(c) 4.022 X 1023 (d) 4.284 X 1022

4. Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.

……………………………………………………………………………………………...

……………………………………………………………………………………………...

……………………………………………………………………………………………...

……………………………………………………………………………………………...

……………………………………………………………………………………………...


18

5. How many grams of neon will have the same number of atoms as 4 g of calcium?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

6. Calculate the number of iron atoms in a piece of iron weighing 2.8 grams.

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………


19

7. What is the mass of 3 moles of Zinc?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

8. What is the ratio of molecules present in 6.6 grams of CO2 and 3.2 grams of SO2?

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………


20

And that is it! Now, we are in a position to solve a self-evaluation test. It is a question

paper of 50 marks to be solved in 1 hour and contains 20 questions. All the questions

are related to what we have learned in this chapter. It would be like an exam-type test.

It is advised to give the test only after completing the text and reading the summary

given at the end. In this test, as the name suggests, you are going to test yourself. If your

score is less than half the total score (i.e. less than 25), then you must attempt the

practice questions given below. Remember to go through these practice questions also.

PRACTISE QUESTIONS

1. Determine the mass of 6.022 X 1023 number of N2 molecules.

2. Calculate the number of particles in-

(i) 8 g of O2 molecules (ii) 2.5 mol of calcium atoms.

3. What is the mass of 2.5 mol of Methane?

4. Find the mass of one molecule of water.

5. Calculate the number of water molecules and number of oxygen and

hydrogen atoms in a drop of water containing 0.03 mol of water.

6. Calculate the actual mass of one atom of carbon if 12 grams of Carbon

contain one mole of Carbon.

7. Calculate mass of Nitrogen (N2) which contains same number of molecules

as are present in 4.4 grams of Carbon-di-oxide (CO2).

8. Atomic mass of gold is 197 u. How many moles of gold are present in an

ornament containing 88.65 grams of gold?

9. How many moles of SO2 have same mass as 3 moles of oxygen?

10. A glass of water contains 5 mol of water. How many molecules of water are

present?

11. What is the mass of a formula unit of Na+Cl-?

12. How many atoms of Silver are present in a silver wire weighing 5.4 grams?

13. Calculate the ratio of molecules present in 16 g of methane and 16 g of

oxygen.

14. Convert into mole. (a) 12 g of oxygen gas (b) 20 g of water (c) 22 g of

carbon-dioxide.

15. Determine the number of bromide ion in 0.2 mole of MgBr2.


21

Series MOLE/1 Code No. 13/15/12/5

Name

This is a self-evaluation test and is to be solved only after understanding the

concepts mentioned in the text.

This question-paper contains questions regarding the concepts learned in the

text.

Please check that this question paper contains 20 questions.

Please write down the serial number of the question paper before attempting

it.

15 minutes time has been allotted to read this question paper.

It is required to fill candidate’s name in the space provided in this question

paper.

The question paper should be completed within the prescribed time limit.

While answering this question paper avoid referring to any text.

Before writing the answers please read the instructions carefully.

Be honest while evaluating yourself.

SELF-EVALUATION TEST

BASICS OF MOLE CONCEPT

Time allowed: 1.15 hour] [Maximum marks: 45


22

General Instructions:

(i) The question paper comprises of two sections, A and B. You are to

attempt both the sections.

(ii) All questions are compulsory.

(iii) There is no overall choice. However, internal choice has been provided

in the last question of five marks category. Only one option in this

question is to be attempted.

(iv) All questions in Section A and all questions of Section B are to be

attempted separately.

(v) Question numbers 1 to 10 in Section A are MCQs. Of these, question

numbers 1 to 5 carry 1 mark each and question numbers 6 to 10 carry

two marks each.

(vi) Question numbers 11 and 12 in Section B are short answer type

questions of two marks each. The answer to these questions should not

exceed 30 words.

(vii) Question numbers 13 to 18 in Section B are also short answer type

questions but carry 3 marks each.

(viii) Question number 19 is a passage-based question and has 3 sub-questions

which are very short answer type and carry 1 mark each.

(ix) Question number 20 in Section B is a long answer type question and

carries five marks.

(x) There is no negative marking for the questions of Section B. However for

each wrong answer in Section A, 1 mark will be deducted.


23

SECTION A

1. Which one of the following statements is true regarding Sodium?

a) 1 g Sodium has 1 mole atoms

b) 1 g Sodium has 6.022 X 1023 atoms

c) 23 g Sodium has 1 mole of atoms

d) 23 g Sodium has 6.022 X 1022 atoms

2. The molar mas of Chloroform (CHCl3) is-

a) 119.5 grams

b) 118 grams

c) 49 grams

d) 50.5 grams

3. Which of the following correctly represents 360 g of water: (i) 2 moles of H2O (ii) 20 moles of water (iii) 6.022 × 1023 molecules of water (iv) 1.2044×1025 molecules of water

a) (i) only

b) (i) and (iv)

c) (ii) and (iii)

d) (ii) and (iv)

4. Mass of one atoms of Oxygen is

a)

grams

b)

grams

c)

grams

d) 8 u

5. Avogadro constant is called so in whose honour?

a) Wilhelm Ostwald

b) Amadeo Avogadro

P.T.O

.


24

c) Wilhelm Avogadro

d) Amadeo Ostwald

6. Which of the following would weigh the highest?

a) 0.2 mole of sucrose (C12 H22 O11)

b) 2 moles of CO2

c) 2 moles of CaCO3

d) 10 moles of H2O

7. Which of the following has maximum number of atoms?

a) 18 grams of H2O

b) 18 gram of O2

c) 18 gram of CO2

d) 18 grams of CH4

8. 3.42 g of sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are- a) 6.68 × 1023

b) 6.09 × 1022

c) 6.022 × 1023

d) 6.022 × 1021

9. Which of the following contains maximum number of molecules?

a) 1g CO2

b) 1g N2

c) 1g H2

d) 1g CH4

10. For the given reaction, H2O + Cl2 + H2S H2SO4 + HCl, the correct statement is:

a) The mole ratio between Cl2 and H2S is 2:1 in balanced reaction

b) The mole ratio between H2O and H2S is 4:1 in balanced reaction

c) 1 mole of H2SO4 is produced from 2 moles of Cl2

d) 4 moles of H2O are required to produce 4 moles of HCl

P.T.O

.


25

SECTION B

11. In a Science laboratory, there are two samples as follows:

SAMPLE A – 2 grams of Hydrogen gas

SAMPLE B – 2 grams of Helium gas

Find a relation between the number of moles of the given two samples.

12. Scientists use a unit called ‘mole’ to count the number of atoms or molecules. Why

don’t they use any other unit like, dozen or gross, to count the number of particles?

13. In the formation of CO, it is found that 2.445 g of carbon combines with 3.260 g of

oxygen. What is the atomic ratio of carbon and oxygen which combine?

14. Calculate number of atoms in 120 gram of Calcium and 120 gram of Iron. Which one

has more number of atoms and how much is the difference?

(Given atomic mass of Calcium = 40 u, Iron = 56 u)

15. If one gram of Sulphur contains x atoms, what will be the number of atoms in one

gram of oxygen? (atomic mass of S = 32u)

16. Calcium chloride when dissolved in water dissociates into its ions according to the

following equation.

CaCl2 (aq) → Ca2+ (aq) + 2Cl– (aq)

Calculate the number of ions obtained from CaCl2 when 222 g of it is dissolved in

water.

17. The mass of one steel screw is 4.11 g. Find the mass of one mole of these steel

screws. Compare this value with the mass of the Earth (5.98 × 1024 kg). Which one of

the two is heavier and by how many times?

18. A currency counting machine counts 6 lakh notes per day. A bank has as many notes

as number of Hydrogen atoms in 24.8 grams of Na2S2O3.5H2O. How many days would

be required to count these notes? Give an approximate answer in terms of power of

ten.

19. Read the following passage carefully and answer the questions that follow: Moles measure quantity of substance. There is a subtle ambiguity about treating “moles” – whether as “mass” or “number”. We take the position that it measures “amount of substance”, which can be either be expressed in terms of mass or in terms of numbers. The two approaches are equivalent and need not be a source of ambiguity any further. We only need to interpret the meaning as appropriate in a particular context.

P.T.O

.


26

a) How is mole related to ‘mass’? b) How is mole related to ‘number’? c) What does mole actually measure?

20. A sample of ethane (C2H6) gas has the same mass as 1.5 × 1020 molecules of

methane (CH4). How many C2H6 molecules does the sample of gas contain?

OR

In photosynthesis, 6 molecules of carbon dioxide combine with an equal number of

water molecules through a complex series of reactions to give a molecule of glucose

having a molecular formula C6H12O6. How many grams of water would be required to

produce 18 g of glucose? Compute the volume of water so consumed assuming the

density of water to be 1 g cm–3.

* * * * *


27

Series MOLE/1 Code No. 13/15/12/5

SOLUTION TO SELF-EVALUATION TEST

BASICS OF MOLE CONCEPT

SECTION A

1. c)

2. a)

3. d)

4. a)

5. b)

6. c)

7. d)

8. a)

9. c)

10. b)

SECTION B

11. Number of moles of Sample A (Hydrogen) is double that of Sample B (Helium).

12. Relative advantage of using mole is that not only number but also mass of 1 mole of a particular substance is always fixed.

13. 1:1

14. Calcium- 1.8066 X 1024; Iron- 1.2904 X 1024 ; Calcium has 5.162 X 1023 more atoms

15. 2x atoms

16. 3.6 132 X 1024 ions

17. Mass of 1 mole of steel screws- 2.475 X 1021 kg; Earth is 2400 times heavier.


28

18. 1018 days

19. a) Mass of 1 mole of a substance is fixed and equals molar mass of the substance. b) 1 mole of a substance always contain Avogadro number of particles. c) Amount of substance- either in terms of mass or number

20. 0.8 X 1020 molecules OR

10.8 grams; Volume- 10.8 cm3.

* * * * *


29

Summary of Mole Concept.

The Avogadro constant, 6.022 X 1023

is defined as the number of atoms in

exactly 12 g of Carbon.

Mole is the amount of substance that contains the same number of particles

(atoms / ions / molecules/ formula units etc.).

1 mole of any species (atoms / ions / molecules/ particles) is that quantity in

number having a mass equal to its atomic mass molecular mass in grams.

Mass of 1 mole of a substance is called its molar mass.

Number of moles = n

Given mass = m

Molar mass = M

Given number of particles = N

Avogadro number = NO

Key formula-

i) =

ii) =

Other formula-

iii) Mass = Number of moles X Molar mass

iv) Number of particles = Number of moles X Avogadro number

v) Mass =

vi) Number of particles =


30

Did you enjoy reading this?

REQUEST FOR FEEDBACK

How did you like the document? How would you grade this document? Is this document

enough with required details? Is there any scope for improvement? Do write to us your

comments and suggestions at [email protected] . Your comments and suggestions are most

welcome. We respect each and every feedback.

© This a document has no copyright because knowledge has got no copyright.

Every effort has been made to avoid errors or omissions in this document. However, some unintentional errors might have crept in for which the

author shall not be held responsible. Any mistake, error or discrepancy brought to Author’s notice shall be taken care of.

mailto:[email protected]

Documents

Basics of Mole Concept