+1 Chemistry - Some Important Questions & Answers
SOME BASIC CONCEPTS OF CHEMISTRY
1. NO and NO2 are two oxides of nitrogen. Which law of chemical combination is
illustrated by these compounds? State the law. Who proposed this law?
Ans: Law of Multiple proportion. It states that when two elements combine to form more
than one compound, the different masses of one of the elements that combine with a fixed
mass of the other, is in a simple whole number ratio. This law was proposed by John
Dalton.
2. State Law of Definite (Constant) proportion. Who proposed this law?
Ans: It states that a given compound always contains exactly the same proportion of
elements by weight. This law was proposed by Joseph Proust.
3. State Law of conservation of mass (matter). Who proposed this law?
Ans: It states that matter can neither be created nor destroyed. Or, in a chemical reaction,
the total mass of reactants is equal to the total mass of products. This law was proposed by
Antoine Lavoisier.
4. Define a.m.u
Ans: 1/12th the mass of a C12 atom is called atomic mass unit (amu).
5. Define 1 mole.
Ans: 1 mole is the amount of substance that contains as many particles as there are atoms in
exactly 12 g C12 isotope.
6. Find the number of oxygen atoms present in 5 moles of glucose (C6H12O6).
Ans: 1 mol glucose contains 6 mol Oxygen atoms.
So, 5 mol glucose contain 6 x 5 = 30 mol Oxygen atoms
= 30 x 6.022 x 1023 Oxygen atoms
7. Write the number of significant figures in the following:
(i) 0.0205 (ii) 3.00 x 10–5 (iii) 1005
Ans: (i) 3 (ii) 3 (iii) 4
8. Define mass percentage.
Ans: It is the percentage of each element present in 100g of a substance.
i.e. percentage composition (mass percent) of an element
= Mass of that element in the compound x 100
Molar mass of the compound
9. What are empirical and molecular formulae?
Ans: Empirical formula is the simplest formula which gives only the ratio of different
elements present in the compound. But molecular formula is the actual formula that gives
the exact number of different elements present in the sample.
+1 CHEMISTRY_SOME IMPORTANT QUESTIONS & ANSWERS 1
,10. A compound contains 4.07% hydrogen, 24.27% carbon and 71.65% chlorine. Its
molecular mass is 98.96. What are the empirical and molecular formulae
Ans:
Element Percentage Atomic mass Percentage/Ato Simple ratio Simplest
mic mass whole no.
ratio
C 24.27 12 24.27/12 = 2.02 2.02/2.02 = 1 1
H 4.07 1 4.07/1 = 4.07 4.07/2.02 = 2 2
Cl 71.65 35.5 71.65/35.5 = 2.02 2.02/2.02 = 1 1
Empirical Formula = CH2Cl
Empirical Formula Mass (EFM) = 12+2+35.5 = 49.5
Molar mass (MM) = 98.96
n = MM/EFM = 98.96/49.5 = 2
Molecular formula = Empirical formula x n
= (CH2Cl) x 2 = C2H4Cl2
11. Find the number of moles and molecules present in 90 g water.
Ans: No. of moles(n) = Given mass in gram (w) = 90 = 5 moles
Molar mass (M) 18
No. of molecules = no. of moles x 6.022x 1023 = 5 x 6.022x 1023 molecules
12. What is limiting reagent?
Ans: It is the reagent which limits a reaction. OR, it is the reagent which is completely
consumed in a chemical reaction.
13. Differentiate between molarity and molality.
Ans: Molarity is defined as the number of moles of solute dissolved per litre of solution.
OR, Molarity (M) = Number of moles of solute (n)
Volume of solution in litre (V)
Molality is defined as the number of moles of the solute present per kilogram (kg) of the
solvent.
OR, Molality (m) = Number of moles of solute
Mass of solvent in kg
Molality is temperature independent, while molarity changes with temperature.
14. Find the molarity of a solution prepared by dissolving 4g of NaOH dissolves in 250 mL
solution.
Ans:
Molarity (M) = Number of moles of solute (n)
Volume of solution in litre (V)
No. of moles of NaOH = Given mass = 4 = 0.1 mol
Molar mass 40
Volume of solution in L = 250/1000 = 0.25 L
Molarity = 0.1 = 0.4M
0.25
+1 CHEMISTRY_SOME IMPORTANT QUESTIONS & ANSWERS 2
, STRUCTURE OF ATOM
1. Give any two characteristic properties of cathode rays.
Ans: (i) They are negatively charged particles.
(ii) They can produce x–rays
2. Write any two characteristic properties of canal rays (anode rays).
Ans: (i) They are positively charged particles.
(ii) Their properties depend on the nature of gas present in the cathode ray tube.
3. What are the important observations and conclusions made by Rutherford in his α–
particle scattering experiment ?
Ans: The important observations are:
i. Most of the α– particles passed through the gold foil without any deviation.
ii. A small fraction of the α–particles was deflected by small angles.
iii. A very few α– particles were rebounded (Or, deflected by nearly 180°).
Conclusions:
i. Since most of the α–particles passed through the foil without any deviation, most
space in the atom is empty.
ii. In an atom, there is a positively charged centre called nucleus.
iii. The volume of the nucleus is negligibly small as compared to the total volume of the
atom.
4. What are the postulates of Rutherford atom model (Planetary model of atom)?
Ans: The important postulates are:
i. All the positive charge and most of the mass of the atom are concentrated at the centre
called nucleus.
ii. Electrons are revolving round the nucleus with a very high speed in circular paths called
orbits.
iii. Electrons and the nucleus are held together by electrostatic forces of attraction.
5. What are the drawbacks of Rutherford atom model?
Ans: (i) He could not explain the stability of the atom.
(ii) He could not explain the electronic structure of atom.
6. What is photoelectric effect?
Ans: It is the phenomenon of ejection of electrons by certain metals (like potassium,
rubidium, caesium etc.) when light of suitable frequency incident on them. The electrons
ejected are called photoelectrons.
7. What are the important characteristics of photoelectric effect? [Write the important
results observed during photoelectric effect].
The important characteristics of photoelectric effect are:
i. The electrons are ejected from the metal surface as soon as the beam of light strikes the
surface.
ii. The number of electrons ejected is proportional to the intensity or brightness of light.
iii. For each metal, there is a minimum frequency (known as threshold frequency [ν0])
below which photoelectric effect is not observed.
+1 CHEMISTRY_SOME IMPORTANT QUESTIONS & ANSWERS 3
SOME BASIC CONCEPTS OF CHEMISTRY
1. NO and NO2 are two oxides of nitrogen. Which law of chemical combination is
illustrated by these compounds? State the law. Who proposed this law?
Ans: Law of Multiple proportion. It states that when two elements combine to form more
than one compound, the different masses of one of the elements that combine with a fixed
mass of the other, is in a simple whole number ratio. This law was proposed by John
Dalton.
2. State Law of Definite (Constant) proportion. Who proposed this law?
Ans: It states that a given compound always contains exactly the same proportion of
elements by weight. This law was proposed by Joseph Proust.
3. State Law of conservation of mass (matter). Who proposed this law?
Ans: It states that matter can neither be created nor destroyed. Or, in a chemical reaction,
the total mass of reactants is equal to the total mass of products. This law was proposed by
Antoine Lavoisier.
4. Define a.m.u
Ans: 1/12th the mass of a C12 atom is called atomic mass unit (amu).
5. Define 1 mole.
Ans: 1 mole is the amount of substance that contains as many particles as there are atoms in
exactly 12 g C12 isotope.
6. Find the number of oxygen atoms present in 5 moles of glucose (C6H12O6).
Ans: 1 mol glucose contains 6 mol Oxygen atoms.
So, 5 mol glucose contain 6 x 5 = 30 mol Oxygen atoms
= 30 x 6.022 x 1023 Oxygen atoms
7. Write the number of significant figures in the following:
(i) 0.0205 (ii) 3.00 x 10–5 (iii) 1005
Ans: (i) 3 (ii) 3 (iii) 4
8. Define mass percentage.
Ans: It is the percentage of each element present in 100g of a substance.
i.e. percentage composition (mass percent) of an element
= Mass of that element in the compound x 100
Molar mass of the compound
9. What are empirical and molecular formulae?
Ans: Empirical formula is the simplest formula which gives only the ratio of different
elements present in the compound. But molecular formula is the actual formula that gives
the exact number of different elements present in the sample.
+1 CHEMISTRY_SOME IMPORTANT QUESTIONS & ANSWERS 1
,10. A compound contains 4.07% hydrogen, 24.27% carbon and 71.65% chlorine. Its
molecular mass is 98.96. What are the empirical and molecular formulae
Ans:
Element Percentage Atomic mass Percentage/Ato Simple ratio Simplest
mic mass whole no.
ratio
C 24.27 12 24.27/12 = 2.02 2.02/2.02 = 1 1
H 4.07 1 4.07/1 = 4.07 4.07/2.02 = 2 2
Cl 71.65 35.5 71.65/35.5 = 2.02 2.02/2.02 = 1 1
Empirical Formula = CH2Cl
Empirical Formula Mass (EFM) = 12+2+35.5 = 49.5
Molar mass (MM) = 98.96
n = MM/EFM = 98.96/49.5 = 2
Molecular formula = Empirical formula x n
= (CH2Cl) x 2 = C2H4Cl2
11. Find the number of moles and molecules present in 90 g water.
Ans: No. of moles(n) = Given mass in gram (w) = 90 = 5 moles
Molar mass (M) 18
No. of molecules = no. of moles x 6.022x 1023 = 5 x 6.022x 1023 molecules
12. What is limiting reagent?
Ans: It is the reagent which limits a reaction. OR, it is the reagent which is completely
consumed in a chemical reaction.
13. Differentiate between molarity and molality.
Ans: Molarity is defined as the number of moles of solute dissolved per litre of solution.
OR, Molarity (M) = Number of moles of solute (n)
Volume of solution in litre (V)
Molality is defined as the number of moles of the solute present per kilogram (kg) of the
solvent.
OR, Molality (m) = Number of moles of solute
Mass of solvent in kg
Molality is temperature independent, while molarity changes with temperature.
14. Find the molarity of a solution prepared by dissolving 4g of NaOH dissolves in 250 mL
solution.
Ans:
Molarity (M) = Number of moles of solute (n)
Volume of solution in litre (V)
No. of moles of NaOH = Given mass = 4 = 0.1 mol
Molar mass 40
Volume of solution in L = 250/1000 = 0.25 L
Molarity = 0.1 = 0.4M
0.25
+1 CHEMISTRY_SOME IMPORTANT QUESTIONS & ANSWERS 2
, STRUCTURE OF ATOM
1. Give any two characteristic properties of cathode rays.
Ans: (i) They are negatively charged particles.
(ii) They can produce x–rays
2. Write any two characteristic properties of canal rays (anode rays).
Ans: (i) They are positively charged particles.
(ii) Their properties depend on the nature of gas present in the cathode ray tube.
3. What are the important observations and conclusions made by Rutherford in his α–
particle scattering experiment ?
Ans: The important observations are:
i. Most of the α– particles passed through the gold foil without any deviation.
ii. A small fraction of the α–particles was deflected by small angles.
iii. A very few α– particles were rebounded (Or, deflected by nearly 180°).
Conclusions:
i. Since most of the α–particles passed through the foil without any deviation, most
space in the atom is empty.
ii. In an atom, there is a positively charged centre called nucleus.
iii. The volume of the nucleus is negligibly small as compared to the total volume of the
atom.
4. What are the postulates of Rutherford atom model (Planetary model of atom)?
Ans: The important postulates are:
i. All the positive charge and most of the mass of the atom are concentrated at the centre
called nucleus.
ii. Electrons are revolving round the nucleus with a very high speed in circular paths called
orbits.
iii. Electrons and the nucleus are held together by electrostatic forces of attraction.
5. What are the drawbacks of Rutherford atom model?
Ans: (i) He could not explain the stability of the atom.
(ii) He could not explain the electronic structure of atom.
6. What is photoelectric effect?
Ans: It is the phenomenon of ejection of electrons by certain metals (like potassium,
rubidium, caesium etc.) when light of suitable frequency incident on them. The electrons
ejected are called photoelectrons.
7. What are the important characteristics of photoelectric effect? [Write the important
results observed during photoelectric effect].
The important characteristics of photoelectric effect are:
i. The electrons are ejected from the metal surface as soon as the beam of light strikes the
surface.
ii. The number of electrons ejected is proportional to the intensity or brightness of light.
iii. For each metal, there is a minimum frequency (known as threshold frequency [ν0])
below which photoelectric effect is not observed.
+1 CHEMISTRY_SOME IMPORTANT QUESTIONS & ANSWERS 3
