First chapter solved MCQs with explanation
1: Isotopes differ in
a) Properties that depends upon mass
b) Arrangement of electrons in orbitals
c) Chemical properties
d) The extent to which they may be affected in the electromagnetic field
Explanation
a is the correct answer
Because by definition the isotopes differ in the number of neutrons and so their masses are different.
Hence The answer a is satisfied
2: Which of the following statements is not true?
a) Isotopes with even atomic masses are comparatively abundant
b) Isotopes with odd atomic masses are comparatively abundant
c) Isotopes with even atomic masses are comparatively abundant
d) Isotopes with even atomic masses and odd atomic numbers are comparatively abundant
Explanation
The correct answer is C
Because the isotopes with even atomic masses and even atomic numbers are comparatively abundant like 8O16, 12Mg24, 14Si28, 20Ca40, and 26Fe56 and make 50% of the earth’s crust.
Hence The answer c is satisfied
3: Many elements have fractional atomic masses. This is because
a) The mass of the atom is itself fractional
b) Atomic masses are average masses of isobars
c) Atomic masses area average masses of isotopes
d) Atomic masses are average masses of isotopes proportional to their relative abundance
Explanation
The correct answer is d
Because the atomic mass depends upon the number of isotopes and their relative % abundance. It is obtained by multiplying the isotopic mass by a fraction of atoms having that mass with percent abundance and dividing by 100.
Hence The answer d is satisfied
4: The mass of one mole of electrons is
a) 1.008 mg
b) 0.55 mg
c) 0.184 mg
d) 1.673 mg
Explanation
The correct answer is b
Mass of electron= 9.1 x10-32 kg
We know that 1 kg = 106
Therefore, mass of one electron= 9.1×10-31 x 106 mg = 9.1 x 10-25 mg
Since 1 mole of electrons = 6.02 x 1023 electrons
Mass of 6.02 x1023 electrons = 9.1 x 10-25 x 6.02 x 1023 = 0.55 mg
Hence The answer b is satisfied
5: 27 g of Al will react completely with how much mass of O2, to produce Al2O3.
a) 8 g of oxygen
b) 16 g of oxygen
c) 32 g of oxygen
d) 24 g of oxygen
Explanation
The correct answer is d
As
27 g of Al = 1 mole of Al
The balanced chemical equation in this case is
4Al + 3O2 —2Al2O3
According to the mole ratio
Al : O2
4 moles : 3 moles
1 : ¾
Mass of O2 = ¾ x32 = 24 g
So the answer d is satisfied
6: The number of moles of CO2 which contain 8.0 g of oxygen
a) 0.25
b) 0.50
c) 1.0
d) 1.50
Explanation
The correct answer is a
As moles of oxygen = 8/16 = 0.5
For 2 moles of oxygen, CO2 = 1 mole
For 1 mole of oxygen, CO2= ½ mole
For 0.5 moles of oxygen, CO2 = ½ x 0.5 = 0.25 moles
Hence The answer a is satisfied
7: The largest number of molecules are present in
a) 3.6 g of H2O
b) 4.8 g of C2H5OH
c) 2.8 g of CO
d) 5.4 g of N2O5
Explanation
The correct answer is a
As by calculating the number of moles of each it becomes clear
Mass of H2O = 3.6 g
Moles of H2O = 3.6g/18 g mol-1 = 0.2
Mass of C2H5OH = 4.6 g
Moles of C2H5OH = 4.6g/46 g mol-1 = 0.1
Mass of CO = 2.8 g
Moles of CO = 2.8g/28 g mol-1 = 0.1
Mass of N2O5 = 5.4 g
Moles of N2O5 = 5.4g/108 g mol-1 = 0.05
We know that the greater the number of moles of a compound greater the number of molecules. So in this case the largest number of molecules are present in water.
Hence The answer a is satisfied
8: One mole of SO2 contains
a) 6.02 x 1023 atoms of oxygen
b) 18.1 x 1023 molecules of SO2
c) 6.02 x 1023atoms of sulfur
d) 4 g of atoms of SO2
Explanation
The correct answer is c
As we know that
One mole of SO2 = 32 + 32 = 64 g
One mole of SO2 results in 2 moles of oxygen and one mole of sulfur.
Therefore,
Number of oxygen atoms = 2 x 6.02 x 1023
Number of sulfur atoms = 6.02 x 1023
Hence the answer c is satisfied
9: The volume occupied by 1.4 g of N2 at S.T.P is
a) 2.24 dm3
b) 22.4 dm3
c) 1.12 dm3
d) 112 dm3
Explanation
The correct answer is c
Because after calculating the moles of nitrogen and using the idea of molar volume it becomes clear
Mass of N2 = 1.4 g
Moles of N2 = 1.4 g / 28 g mol-1 = 0.05
1 mole of N2 at S.T.P has volume = 22.414 dm3
0.05 mole of N2 at S.T.P has volume = 22.414 x 0.05 = 1.12 dm3
Hence the answer c is satisfied
10: A limiting reactant is the one which
a) Is taken in lesser quantity in grams as compared to another reactant
b) is taken in lesser quantity in volume as compared to the other
c) Carries the maximum amount of the product which is required
d) Gives the minimum amount of the product under consideration
Explanation
The correct answer is d
Because according to the definition of limiting reactant it is the reagent that gives the minimum amount of the product and is finished earlier.
Hence the answer d is satisfied