PROFESSOR SERIES
Professor easy notes for
CHAPTER NO 1
“Basic concepts”
Class 11th
“Solved Exercise + Old papers board"
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CHAPTER # 1
BASIC CONCEPTS
1
PROFESSOR EASY NOTES
Important Short questions (Exercise is also added)
(1) What is atomic mass unit (a.m.u)? Give its value in grams. (2008) (2009)
The unit used to express the relative atomic mass is called atomic mass unit. It is 1/12th of the mass
of one carbon atom. 1 amu = 1.661× 10-27 kg or 1 amu = 1.661× 10-24 g
(2) Law of conversation of mass has to be considered during stoichiometric calculations. (2008)
Stoichiometric calculations are based on balanced chemical equation. During this it is assumed that
matter is neither created nor destroyed but changes from one form to another. So Law of
conversation of mass has to be considered during stoichiometric calculations otherwise with
unbalanced chemical equations stoichiometric calculations will not be possible.
(3) One mole of N2, CO2 and H2 contains equal number of molecules. Give reason. (2008)
1 mole of CO2
= 6.023 × 1023 molecules
1 mole of N2
= 6.023 × 1023 molecules
1 mole H2
= 6.023 × 1023 molecules
Since all the gases has same number of moles i.e. N2, H2 and CO2 have their one mole so they
contains equal number of molecules.
(4) No individual neon atom in the sample of the element has a mass of 20.18 amu. (2017) (2018)
OR
Atomic masses may be expressed in fractions, why? (2009)
20
21
22
A sample of neon consists of 10Ne, 10Ne and 10Ne in the percentages of 90.92%, 0.26% and 8.82%
respectively. The average atomic mass of Ne can be calculated as
(20×90.92)+(21×0.26)+(22×8.82)
= 20.18 amu
Average atomic mass =
100
Hence 20.18 amu is the average atomic mass of neon and no individual neon in the sample that has a
mass of 20.18 amu.
(5) NaCl has 58.5 amu as formula mass and not the molecular mass, justify it? (2009)
NaCl is an ionic compound and does not exist in molecular form. Therefore NaCl is a formula unit
and has 58.5 amu as formula mass and not the molecular mass.
(6) Define molecular ion. How it is generated?
OR
What is molecular ion? Give one example. (2009) (2010) (2012) (2013)
When a molecule loses or gains an electron, molecular ion is formed. For example CH4+, CO+, N2+.
Cationic molecular, ions are more abundant than anionic ions.
These can be generated by passing high energy electron beam as α-particles or X-rays through a gas.
The breakdown of molecular ions obtained from the natural products can give important information
about their structure.
(7) Calculate the mass in grams of 2.74 moles of KMnO4. (2010)
No of moles of KMnO4
= 2.74 moles
Molar mass of KMnO4
= 158 g/mol
[(39) + (55) + (16×4) = 158]
Mass of KMnO4
= No. of moles × Molar mass of KMnO4
Muhammad Shahid
= 2.74 × 158 = 432.92gram
A-One Professors Academy of
(8) Define ions. Give two examples. (2011)
Sciences Jauharabad
OR
What are ions? Under what conditions they are produced? (2017)
Ions are those species which carry either positive or negative charge.
By ionization of an ionic compound in water.
e.g.
NaCl
Na+ + ClPositive ions are produced by passing high energy electron beam, α-particles or X-rays through a
gas.
e.g.
Na  Na+ + eFor 9th, 10th, FSs and ICs Notes, Test Papers, Paper Schemes, and other study realted stuff Visit taleemcity.com
CHAPTER # 1
BASIC CONCEPTS
2
PROFESSOR EASY NOTES
Negative ions are produced by the addition of an electron to a neutral species.
e.g.
Cl + e-  Cl(9) Write the formulas used for the determination of percentage of C & H. (2012)
The percentage of carbon can be calculated by using following formula:
12.00
Mass of CO2
% of carbon =
×
× 100
Mass of organic compund
44.00
The percentage of hydrogen can be calculated by using following formula:
Mass of H2 O
2.016
% of hydrogen =
×
× 100
Mass of organic compund
18
(10) What is limiting reactant? How it is identified?(2012) (2013) (2015)
The reactant which controls (limits) the amount of product formed during a chemical reaction is
called limiting reactant. It can be identified by following steps:
 Calculate the number of moles from the given amount of reactant.
 Find out the number of moles of the product with the help of a balanced chemical equation.
 Identify the reactant which produces the least amount of product as limiting reactant.
(11) What is stoichiometry? Give its assumptions. (2012) (2013) (2016)
Stoichiometry is a branch of chemistry which gives a quantitative relationship between reactants
and products in a balanced chemical equation. It has two assumptions:
 All the reactants are completely converted into the products.
 No side reaction occurs.
(12) What is Avogadro’s number? Give an example. (2012)
Avogadro’s number is the number of atoms, molecules and ions in one gram atom of an element,
one gram molecule of a compound and one gram ions of a substance, respectively. For example
1.008 g of Hydrogen = 1 mole of H
= 6.02 × 1023 atoms of H
18 g of H2O
= 1 mole of H2O
= 6.02 × 1023 molecules of H2O
22= 1 mole of SO4
= 6.02 × 1023 ions of SO4296 g of SO4
(13) Molecular formula is integral multiple of empirical formula. Give comments. (2012)
The empirical formula gives only the simplest whole number ratio of atoms of each element in a
compound, while molecular formula tells the actual number of atoms of each element in a molecule.
So empirical formula is multiplied with a suitable integer “n” to get the molecular formula. Where
“n” is the ratio molecular mass and empirical formula mass. For example benzene 6 × (CH) = C6H6
(14) Define (a) Limiting reactant (b) Atomicity. (2012)
Limiting reactant:
The reactant which controls (limits) the amount of product formed during a chemical reaction is
called limiting reactant. For example burning of coal to form CO2. Coal is limiting reactant.
Atomicity:
The number of atoms present in a molecule is called its atomicity. For example the atomicity of O2
is two.
(15) What is meant by atomicity? Explain with two examples. (2015) (2017)
The number of atoms present in a molecule is called its atomicity. The molecule can be
monoatomic, diatomic and triatomic etc. If the molecule contains one atom it is monoatomic, if it
contains two atoms it is diatomic, and if it contains three atoms it is triatomic. Molecules of
elements may contain one two or more same type of atoms. For example He, Cl2, O3, P4, S8. The
molecules of compounds consist of different kind of atoms. For example HCl, NH3, H2SO4,
C6H12O6.
(16) A compound may have same empirical and molecular formula. Justify it. (2015)
There are many compounds, which have same empirical formula and molecular formula. For
example H2O, CO2, NH3 and C12H22O11 have the same empirical and molecular formulas. Their
simple multiple “n” is unity. Actually value of “n” is the ratio of molecular mass and empirical
formula mass.
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CHAPTER # 1
BASIC CONCEPTS
3
PROFESSOR EASY NOTES
(17) Distinguish b/w actual yield and theoretical yield. (2015)
Actual Yield:
The amount of the products obtained as a result of a chemical reaction is called actual yield. It is
based on experiment.
Theoretical (Experiment) Yield:
The amount of the products calculated from the balanced chemical equation is called theoretical yield.
(18) What is percentage yield? Give its significance. (2015)
Percentage yield is actually the efficiency of a reaction. It tell us how much product we have
obtained after a chemical reaction.
It can be obtained by comparing theoretical and actual yield in the form of the percentage yield.
Actual Yield
% yield =
× 100
Theoretical yield
(19) Define mass spectrometer. (2016)
Mass spectrometer is an instrument which is used to measure the exact masses of different isotopes
of an element.
(20) How many molecules of water are there in 10 gram of ice? (2016)
Mass in gram
Number of molecules (Ice) =
× NA
Muhammad Shahid
Number of molecules (Ice) =
Molar mass
10
18
× 6.02 × 1023
A-one Professors Academy of
sciences Jauharabad
Number of molecules (Ice) = 3.34 × 1023 molecules
(21) What is the justification of two peaks in the mass spectrum of bromine, while for iodine only
one peak at 127 a.m.u is indicated? (2017)
(1) Bromine has two naturally occurring isotopes with almost equal relative abundance therefore;
its mass spectrum shows two strong peaks.
(2) While iodine has only one naturally occurring isotopes, therefore, its spectrum shows only one
peak.
(22) Why theoretical yield of a chemical reaction is greater than the actual yield? (2017)
Theoretical yield of a chemical reaction is greater than the actual yield because it is calculated
from a balanced chemical equation where we supposed that all the reactants are converted into
products and no side reaction occurred.
(23) Why the actual yield is always less than the theoretical yield? (2017) (2018)
The actual yield is always less than theoretical yield due to following reasons.
 Inexperience worker wastes a significant amount of product.
 The reversible reactions are never completed.
 Side reaction may occur.
 All the reactant may not be converted into products.
 Mechanical loss may occur like during e.g. Filtration, evaporation, crystallization, distillation etc.
(24) Write only four names of any four methods employed for the separation of isotopes. (2018)
The separation of isotopes can be done by using following methods.
 Gaseous diffusion
 Thermal diffusion
 Distillation
 Ultracentrifuge
 Electromagnetic separation
 Laser separation
(25) Define gram atom by giving an example. (2018)
The atomic mass of an element expressed in grams is called gram atom.
For example 1 gram atom of Hydrogen = 1.008 g
(26) Write down limitations of a chemical equation. (2018)
The chemical equation has following limitations
They don’t tell about the conditions of reactions.
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CHAPTER # 1
BASIC CONCEPTS
4
PROFESSOR EASY NOTES
They don’t tell us rate of reaction.
These can also be written for such reactions that does not occur.
These cannot tell about the time to complete the reaction.
(27) What is the function of ionization chamber in mass spectrometer? (2018)
In mass spectrometer the function of ionization chamber is to ionize the vapours of the substance.
For this purpose vapours are passed into ionization chamber. In this fast moving electrons are
thrown upon them. As a result gaseous atoms are ionized and positive ions are produced.
(28) Calculate the mass of 10-3 moles of water?
No of moles of water
= 10-3 moles
Molar mass of water
= 18 g/mol
Mass of water
= No. of moles × Molar mass of water
= 10-3 × 18 = 1.8 × 10-2 gram = 0.018 g.
(29) What are isotopes?
Atoms of the same element, having same atomic number but different mass number are called
isotopes.
The phenomenon of isotopy was discovered by Soddy.
Examples
12 13 14
Carbon has three isotopes written as 6C, 6C, 6C and expressed as C-12, C-13, C-14, having 6, 7 and
8 neutrons in their nuclei respectively.
Hydrogen has three isotopes:
1
1H
2
3
Protium
1H Deuterium
1H Tritium
(30) Which information we can get from mass spectrum?
In mass spectrometer, the result is recorded in the form of graph containing peaks. The relative
numbers of ions are present along y-axis (ordinate) and m/e values of ions are present along x-axis
(abscissa). This is called spectrum. It gives following information
(1) The number of peaks gives the number of isotopes of an element.
(2) The height of peaks gives the relative abundance of isotopes.
(3) The position of peak gives the mass of the isotopes.
(31) Justify the following statement:
 23 gram of sodium and 238 gram of uranium have equal number of atoms in them.
1 mole of Na = 23g
1 mole of U = 238g
Since one mole of each element contains Avogadro’s number of atoms and there is one mole of
each of Na and U. hence 23g of Na and 238g of U contains equal number of atoms i.e. 6.02 × 1023.
 Mg atom is twice heavier than that of carbon?
One atom of carbon contains 6 protons and 6 neutrons in its nucleus and its atomic mass on
atomic mass unit scale is 12 amu.
While one atom of Mg contains 12 protons and 12 neutrons in its nucleus and its atomic mass on
24𝑎𝑚𝑢
atomic mass unit scale is 24amu. Thus,
= 2. Hence, one atom of Mg is twice heavier than
12𝑎𝑚𝑢
that of one atom of Carbon.
 180 gram of glucose and 342 gram of sucrose have same number of molecules but different
number of atoms.
180g of glucose = 1 mole
342g of sucrose = 1 mole
1 mole of each compound contains Avogadro’s number of molecules. Hence, 180 g of glucose
(1mole) and 342 g (1mole) of sucrose contain equal number of molecules i.e. 6.02 × 1023
Since one molecule of glucose (C6H12O6) contains 24 atoms. Whereas, one molecule of sucrose
(C12H22O11) contains 45 atoms, therefore, equal number of molecule of glucose and sucrose will
have different number of atoms.
 4.9 g of H2SO4 when completely ionized in water have equal number of positive and negative
charges but the number of positively charge ions is twice the number of negatively charge ions.
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CHAPTER # 1
BASIC CONCEPTS


(32)



5
PROFESSOR EASY NOTES
H2SO4 ionizes in solution as
H2SO4
2H+ + SO42Muhammad Shahid
This balance equation shows that
A-one Professors Academy of
sciences Jauharabad
One mole of H2SO4 produces
Number of positively charged ions (H+ ions) = 2
Number of negatively charged ions (SO42-) = 1
Number of positive charge = 2 (due to two H+ ions)
Number of negative charge = 2 (due to two negative charge on SO42-)
Hence whatever the amount of H2SO4, it will always produce equal number of positive and negative
charges but number of positively charged ions will be twice the number of the negative charged ions.
One mg of K2Cr2O7 has thrice the number of ions than the number of molecules when ionized
in water.
K2Cr2O7 ionizes as
K2Cr2O7
2K+ + Cr2O72This equation shows that 1 formula unit of K2Cr2O7 produces two K+ ions and one Cr2O72- ion in
solution. Thus a total of three ions are produced by the ionization of 1 formula unit of K2Cr2O7.
Hence whatever be the amount of K2Cr2O7. The number of ions in its solution will always be thrice
than the number of its formula units (molecules).
Two grams of H2, 16 g of CH4 and 44 g of CO2 occupy separately the volume of 22.414 dm3,
although the size and masses of molecules of these gases are very different from each other.
2 grams of H2
= 1 mole = 6.023 × 1023 molecules
16 grams of CH4
= 1 mole = 6.023 × 1023 molecules
44 grams of CO2
= 1 mole = 6.023 × 1023 molecules
Since 2 grams of H2, 16 grams of CH4 and 44 grams of CO2 contains equal numbers of molecules
and according to Avogadro’s law, equal molecules of all the gases at S.T.P. occupy the same volume
i.e. 22.414 dm3.
In gases distance between two molecules is approximately 300 times its own diameter. Thus, volume
occupied by gas molecule does not depends upon the size or mass of molecules and it only depends
upon the numbers of molecules.
Hence equal molecules of H2, CH4 and CO2 at STP will occupy same volume i.e. 22.414 dm3.
Explain the following with reasons
Many chemical reactions taking place in our surrounding involve the limiting reactant.
The reactant which controls (limits) the amount of product formed during a chemical reaction is
called limiting reactant. In our surrounding there are many chemical reactions take place which
involve limiting reactants some of these reactions are:
(i) Burning of coal to form CO2. Coal is limiting reactant.
(ii) Burning of natural gas to form CO2 and H2O. Here natural gas is our limiting reactant.
(iii) Rusting of iron, iron is limiting reactant.
In above reactions oxygen is always in excess, while other reactants are consumed earlier. So other
reactants are limiting reactants.
One mole of H2SO4 should completely react with two moles of NaOH. How does Avogadro’s
number help to explain it?
H2SO4 + 2NaOH  Na2SO4 + H2O
In the above chemical reaction
1 molecule of H2SO4 requires
= 2 formula units of NaOH.
23
1 × 6.02 × 10 molecules of H2SO4 requires
= 2 × 6.02 × 1023 formula units of NaOH or
1 mole of H2SO4 requires
= 2 moles of NaOH
Hence, One mole of H2SO4 should completely react with two moles of NaOH.
One mole of H2O has two moles of bond, three moles of atoms, ten moles of electrons and
twenty eight moles of total fundamental particles present in it.
One molecule of H2O has two bonds therefore one mole of H2O has 2 moles of bonds.
One molecule of H2O has three atoms (Two Hydrogen atoms and one Oxygen atom) therefore one
mole of H2O has three moles of atoms.
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CHAPTER # 1
BASIC CONCEPTS
6
PROFESSOR EASY NOTES
One molecule of H2O has 10 electrons (2 electrons of 2 H and 8 electrons of 1 Oxygen atom)
therefore one mole of H2O has 10 moles of electrons.
One molecule of H2O has twenty eight fundamental particles i.e.10 electrons (2 e- of H + 8 e- of O) +
10 protons (2 protons of H + 8 protons of O) & 8 neutrons. Therefore one mole of H2O has 28 moles
of total fundamental particles present in it.
 N2 and CO has same number of electrons, protons and neutrons.
Both N2 and CO have same number of electrons, protons and neutrons as it is clear from the
following explanation.
For N2
Muhammad Shahid
No. of electrons in N2
= 7 + 7 = 14
A-one Professors Academy of
No. of protons in N2
= 7 + 7 = 14
sciences Jauharabad
No. of neutrons
= 7 + 7 = 14
For CO
Number of electrons in C = 6
No. of electrons in O
=8
Total no. of electrons
= 6 + 8 = 14
No. of protons in C
=6
No. of protons in O
=8
Total no. of protons
= 6 + 8 = 14
No. of neutrons in C
=6
No. of neutrons in O
=8
Total no. of neutrons
= 6 + 8 = 14
Hence N2 and CO has same number of electrons, protons and neutrons.
(33) Write down briefly the principle of mass spectrometry.
In mass spectrometry a substance is first volatilized and then ionized with the help of high energy beam
of electrons. The gaseous positive ions, thus formed, are separated on the basis of their mass to charge
ratio (m/e) and then recorded in the form of peaks.
Important Long questions of previous board papers
(1) What is limiting reactant? How can you determine it? Explain with a chemical reaction.
(2008)
OR
(2) Define limiting reactant. How it controls the amount of products? Give example.
(2009)
(3) What is mass spectrometer? How it is used to determine the relative atomic masses?
(2009)
(4) Calculate the number of grams of K2SO4 and water produced when 14 g of KOH are reacted with
excess of H2SO4, also calculate the number of molecules of water produced.
(2010)
(5) Write steps involved in determination of empirical formula of a compound?
(2012)
(6) NH3 gas can be prepared by heating together two solids NH4Cl and Ca(OH)2. If a mixture containing
100 gram of each solid is heated then, calculate the number of grams of NH3 produced. (2011) (2015)
2NH4Cl + Ca(OH)2  CaCl2 + 2NH3 + 2H2O
(7) What is empirical formula? Discuss how empirical formula is determined by combustion analysis? (2014)
(8) A sample of liquid consisting of carbon, hydrogen and oxygen was subjected to combustion analysis,
0.5439 g of the compound gave 1.039 g of CO2, 0.6369 g of H2O. Determine the empirical formula of
the compound.
(2016)
(9) A well-known gas is enclosed in a container having volume 500 cm3 at S.T.P. its mass comes out to be
0.72 g. What is the molar mass of this gas?
(2017)
(10) When lime (CaCO3) is roasted, quick lime (CaO) is produced according to the following equation.
The actual yield of CaO is 2.5 kg, when 4.5 kg of lime stone is roasted. What is the percentage yield
of this reaction?
(2017)
CaCO3  CaO + CO2
(11) Ethylene glycol is used as automobile antifreeze. It has 38.7% carbon, 9.7% hydrogen and 51.6%
oxygen. Determine its empirical formula.
(2018) (2018)
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