SOME BASIC CONCEPTS OF CHEMISTRY
IMPORTANT QUESTIONS AND THEIR ANSWERS
LEVEL 1 QUESTIONS (Easy)
1. Define the term 'Mole' in chemistry.
Answer:
The mole is the SI unit of measurement used to express the amount of a substance. One mole
of a substance contains Avogadro's number of entities, which is approximately 6.022 x 10^23.
2. Explain the difference between molecular mass and molar mass.
Answer:
Molecular mass is the sum of the atomic masses of all the atoms in a molecule, while molar
mass is the mass of one mole of a substance. Molar mass is expressed in g/mol and is
numerically equal to the molecular mass but has units.
3. How do you calculate the number of moles in a given mass of a substance?
Answer:
The number of moles (n) can be calculated using the formula: n = (Given mass in grams) /
(Molar mass in g/mol).
4. Define empirical formula and molecular formula.
Answer:
The empirical formula represents the simplest whole-number ratio of different atoms in a
compound. The molecular formula represents the actual number of atoms of each element in
a molecule.
5. What is Avogadro's law?
Answer:
Avogadro's law states that equal volumes of gases, at the same temperature and pressure,
contain an equal number of molecules. This implies that the ratio of volumes of gases in a
chemical reaction corresponds to the ratio of small whole numbers.
6. Explain the concept of limiting reactant in a chemical reaction.
Answer:
The limiting reactant is the reactant that is completely consumed in a chemical reaction,
limiting the amount of product that can be formed. The other reactant is called the excess
reactant, as there is more of it than required for the reaction.
, 7. How does concentration differ from density in chemistry?
Answer: Concentration refers to the amount of solute present in a given amount of solution,
expressed as moles per unit volume (e.g., mol/L). Density, on the other hand, is the mass per
unit volume of a substance, typically expressed in g/cm³ or kg/m³.
8. Explain the concept of empirical and molecular formulas with an example.
Answer: The empirical formula represents the simplest whole-number ratio of elements in a
compound. The molecular formula gives the actual number of each type of atom in a
molecule. For example, the empirical formula of hydrogen peroxide is HO, while its
molecular formula is H2O2.
LEVEL 2 QUESTIONS (Intermediate)
1. Define the term 'Atomic Mass Unit' (AMU).
Answer:
Atomic Mass Unit (AMU) is a unit of mass used to express atomic and molecular weights. It
is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear
and electronic ground state, and it is approximately equal to 1.66 x 10^-27 kg.
2. Explain the difference between empirical formula and molecular formula with an example.
Answer:
The empirical formula shows the simplest whole-number ratio of different atoms in a
compound, while the molecular formula gives the actual number of each type of atom in a
molecule. For example, the empirical formula of glucose is CH2O, while its molecular
formula is C6H12O6.
3. Calculate the molecular mass of water (H2O) using the atomic masses: H = 1 g/mol, O =
16 g/mol.
Answer:
Molecular mass = (2 × atomic mass of H) + atomic mass of O
Molecular mass = (2 × 1 g/mol) + 16 g/mol = 18 g/mol
4. State Dalton's Atomic Theory.
Answer:
Dalton's Atomic Theory states that:
- All matter is composed of indivisible particles called atoms.
- Atoms of the same element are identical in size, mass, and chemical properties.
- Atoms of different elements have different properties.
- Atoms combine in simple, whole-number ratios to form compounds.
- In chemical reactions, atoms are rearranged, separated, or combined.
IMPORTANT QUESTIONS AND THEIR ANSWERS
LEVEL 1 QUESTIONS (Easy)
1. Define the term 'Mole' in chemistry.
Answer:
The mole is the SI unit of measurement used to express the amount of a substance. One mole
of a substance contains Avogadro's number of entities, which is approximately 6.022 x 10^23.
2. Explain the difference between molecular mass and molar mass.
Answer:
Molecular mass is the sum of the atomic masses of all the atoms in a molecule, while molar
mass is the mass of one mole of a substance. Molar mass is expressed in g/mol and is
numerically equal to the molecular mass but has units.
3. How do you calculate the number of moles in a given mass of a substance?
Answer:
The number of moles (n) can be calculated using the formula: n = (Given mass in grams) /
(Molar mass in g/mol).
4. Define empirical formula and molecular formula.
Answer:
The empirical formula represents the simplest whole-number ratio of different atoms in a
compound. The molecular formula represents the actual number of atoms of each element in
a molecule.
5. What is Avogadro's law?
Answer:
Avogadro's law states that equal volumes of gases, at the same temperature and pressure,
contain an equal number of molecules. This implies that the ratio of volumes of gases in a
chemical reaction corresponds to the ratio of small whole numbers.
6. Explain the concept of limiting reactant in a chemical reaction.
Answer:
The limiting reactant is the reactant that is completely consumed in a chemical reaction,
limiting the amount of product that can be formed. The other reactant is called the excess
reactant, as there is more of it than required for the reaction.
, 7. How does concentration differ from density in chemistry?
Answer: Concentration refers to the amount of solute present in a given amount of solution,
expressed as moles per unit volume (e.g., mol/L). Density, on the other hand, is the mass per
unit volume of a substance, typically expressed in g/cm³ or kg/m³.
8. Explain the concept of empirical and molecular formulas with an example.
Answer: The empirical formula represents the simplest whole-number ratio of elements in a
compound. The molecular formula gives the actual number of each type of atom in a
molecule. For example, the empirical formula of hydrogen peroxide is HO, while its
molecular formula is H2O2.
LEVEL 2 QUESTIONS (Intermediate)
1. Define the term 'Atomic Mass Unit' (AMU).
Answer:
Atomic Mass Unit (AMU) is a unit of mass used to express atomic and molecular weights. It
is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear
and electronic ground state, and it is approximately equal to 1.66 x 10^-27 kg.
2. Explain the difference between empirical formula and molecular formula with an example.
Answer:
The empirical formula shows the simplest whole-number ratio of different atoms in a
compound, while the molecular formula gives the actual number of each type of atom in a
molecule. For example, the empirical formula of glucose is CH2O, while its molecular
formula is C6H12O6.
3. Calculate the molecular mass of water (H2O) using the atomic masses: H = 1 g/mol, O =
16 g/mol.
Answer:
Molecular mass = (2 × atomic mass of H) + atomic mass of O
Molecular mass = (2 × 1 g/mol) + 16 g/mol = 18 g/mol
4. State Dalton's Atomic Theory.
Answer:
Dalton's Atomic Theory states that:
- All matter is composed of indivisible particles called atoms.
- Atoms of the same element are identical in size, mass, and chemical properties.
- Atoms of different elements have different properties.
- Atoms combine in simple, whole-number ratios to form compounds.
- In chemical reactions, atoms are rearranged, separated, or combined.
