Free NCERT Solutions For Class 11 Chemistry Chapter 1 : Some Basic Concept Of Chemistry Free PDF Download

Question 1: Calculate the molecular mass of the following:
(i) HO2
(ii) CO2
(iii) CH4

Solution:1

Question 2:
Calculate the mass percent of different elements present in sodium sulphate (Na2SO4).

Question 3: Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1%
dioxygen by mass.

Question 4:
Calculate the amount of carbon dioxide that could be produced when
(i) 1 mole of carbon is burnt in air.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.

Question 5:
Calculate the mass of sodium acetate (CH3COONa) required to make 500 mL of 0.375 molar
aqueous solution. Molar mass of sodium acetate is 82.0245 g mol-1

Question 6:
Calculate the concentration of nitric acid in moles per litre in a sample which has a density,
1.41g mL-1 and the mass percent of nitric acid in it being 69%.

Solution 6:
Mass percent of nitric acid in the sample = 69% [Given]
Thus, 100 g of nitric acid contains 69 g of nitric acid by mass.
Molar mass of nitric acid (HNO3)

Question 7:
How much copper can be obtained from 100 g of copper sulphate (CuSO4)?

Question 8:
Determine the molecular formula of an oxide of iron in which the mass percent of iron and
oxygen are 69.9 and 30.1 respectively. Given that the molar mass of the oxide is 159.69g mol-1.

Question 9:
Calculate the atomic mass (average) of chlorine using the following data:

The average atomic mass of chlorine = 35.4527 u

The average atomic mass of chlorine = 35.4527 u

Question 10:
In three moles of ethane (C2H6), calculate the following:
(i) Number of moles of carbon atoms.
(ii) Number of moles of hydrogen atoms.
(iii)Number of molecules of ethane.

Question 12: If the density of methanol is 0.793 kg L-1, what is its volume needed for making 2.5 L of its
0.25 M solution.

Question 13:
Pressure is determined as force per unit area of surface. The SI unit of pressure,
Pascal is as shown below:
1Pa = 1N m-2
If mass of air at sea level is 1034 g cm-2
, calculate the pressure in Pascal

Question 14:
What is the SI unit of mass? How is it defined?

Solution14:
The SI unit of mass is kilogram (kg). 1 Kilogram is defined as the mass equal to the mass of
the international prototype of kilogram.

Question 15:
Match the following prefixes with their multiples:

Question 16:
What do you mean by significant figures?

Solution16:
Significant figures are those meaningful digits that are known with certainty.
They indicate uncertainty in an experiment or calculated value. For example, if 15.6 mL is the
result of an experiment, then 15 is certain while 6 is uncertain, and the total number of
significant figures are 3.
Hence, significant figures are defined as the total number of digits in a number including the
last digit that represents the uncertainty of the result

Question 17:
A sample of drinking water was found to be severely contaminated with chloroform, CHCl3,
supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass). (i) Express this in percent by mass.
(ii) Determine the molality of chloroform in the water sample.

Question 18:
Express the following in the scientific notation:
(i) 0.0048
(ii) 234,000
(iii)8008
(iv)500.0
(v) 6.0012

Question 19:
How many significant figures are present in the following?
(i) 0.0025
(ii) 208 (iii)5005
(iv)126,000
(v) 500.0
(vi)2.0034

Question 20:
Round up the following upto three significant figures.
(i) 34.216
(ii) 10.4107
(iii)0.04597
(iv)2808

Solution 20:
(i) 34.2
(ii) 10.4
(iii)0.0460
(iv)2810

Question 21:
The following data are obtained when dinitrogen and dioxygen react together to form different
compounds:
Mass of dinitrogen Mass of dioxygen
(i) 14 g 16 g
(ii) 14 g 32 g
(iii) 28 g 32 g (iv) 28 g 80 g
(a) Which law of chemical combination is obeyed by the above experimental data? Give its
statement.
(b) Fill in the blanks in the following conversions:
(i) 1 km = ……………………. mm ……………………. pm
(ii) 1 mg = ……………………. kg ……………………. ng
(iii)1 mL = ……………………. L ……………………. dm3

Question 22:
If the speed of light is 3.0*108 ms-1, calculate the distance covered by light in 2.00 ns.:

Solution 22:
According to the question:

Question 23:
In a reaction
A + B2->AB2
Identify the limiting reagent, if any in the following reaction mixtures.
(i) 300 atoms of A + 200 molecules of B
(ii) 2 mol A + 3 mol B
(iii)100 atoms of A + 100 molecules of B
(iv)5 mol A+ 2.5 mol B
(v) 2.5 mol A + 5 mol B

Solution 23:
A limiting reagent determines the extent of a reaction. It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed.
(i) According to the given reaction, 1 atom of A reacts with 1 molecule of B. thus, 200 molecules of B will react with 200 atoms of A, thereby leaving 100 atoms of A unused. Hence, B is the limiting reagent.
(ii) According to the reaction, 1 mol of A reacts with 1 mol of B. thus, 2 mol of A will react with only 2 mol of B. As a result, 1 mol of A will not be consumed. Hence, A is the limiting reagent.
(iii)According of the given reaction, 1 atom of A combines with 1 molecule of B. the mixture is stoichiometric where no limiting reagent is present.
(iv)1 mol of atom A combines with 1 mol of molecule B. Thus, 2.5 mol of B will combine
with only 2.5 mol of A. As a result, 2.5 mol of A will be left as such. Hence, B is the limiting reagent.
(v) According to the reaction, 1 mol of atom A combines with 1 mol of molecule B. Thus, 2.5 mol of A will combine with only 2.5 mol of B and the remaining 2.5 mol of B will be left as such. Hence, A is the limiting reagent.

Question 24:
Dinitrogen and dihydrogen react with each other to produce ammonia according to the
following chemical equation: N 2(g)+ H 2(g ) ->2NH 3(g )
(i) Calculate the mass of ammonia produced if 2.00*103g dinitrogen reacts with 1.00*103gof dihydrogen.
(ii) Will any of the two reactants remain unreacted?
(iii)If yes, which one and what would be its mass?

Question 25: How are 0.50 mol Na2CO3 and 0.50 M Na2CO3different?

Question 26: If ten volumes of dihydrogen gas react with five volumes of dioxygen gas, how many volumes of water vapour would be produced?

Solution 26:
Reaction of dihydrogen with dioxygen can be written as:
2 H2(g) + O 2(g) ->2H 2O ( g)
Now, two volumes of dihydrogen react with one volume of dihydrogen to produce two
volumes of water Vapour.
Hence, ten volumes of dihydrogen will react with five volumes of dioxygen to produce ten
volumes of water Vapour.

Question 27:
Convert the following into basic units:
(i) 28.7 pm
(ii) 15.15 pm
(iii)25365 mg

Question 28: Which one of the following will have largest number of atoms?
(i) 1 g Au (s)
(ii) 1 g Na (s)
(iii)1 g Li (s)
(iv)1 g of CI2(g)

Question 29:
Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is
0.040 (assume the density of water to be one).

Question 30:
What will be the mass of one 12C atom in g?

Question 31:
How many significant figures should be present in the answer of the following calculations?

Question 32:
Use the data given in the following table to calculate the molar mass of naturally occurring
argon isotopes:

Question 33:
Calculate the number of atoms in each of the following
(i) 52 moles of Ar
(ii) 52 u of He
(iii) 52 g of He.

Question 34:
A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen
gives 3.38 g carbon dioxide, 0.690 g water and no other products. A volume of 10.0 L
(measured at STP) of this welding gas is found to weigh 11.6 g. Calculate
(i) empirical formula,
(ii) molar mass of the gas, and
(iii) molecular formula.

Question 35:
Calcium carbonate reacts with aqueous HCl to given CaCl2 and CO2 according to the reaction,
CaCO 3(s) +2HCl (aq)-> CaCl2(aq) + CO 2(g)2+H 2O(l) What mass of CaCO3 is required to react completely with 25 mL of 0.75 M HCl?

Solution 35:
0.75 M of HCI =0.75 mol of HCl are present in 1 L of water

Question 36:
Chlorine is prepared in the laboratory by treating manganese dioxide (MnO2) with aqueous
hydrochloric acid according to the reaction
4HCl(aq) + MnO2(l)-> MnCl2(aq) +cl2(g)
How many grams of HCl react with 5.0 g of manganese dioxide?