Answer: The gay lussac’s law of combining volumes states that the relative volumes of gases are in the ratio of small whole numbers at constant temperature and pressure.
Q6. What is the volume of 6.022 X 1023 molecules of hydrogen at NTP?
22.4 litres
11.2 litres
1 litre
2 litres
Answer: (a), 6.022 X 1023 molecules of hydrogen contain 22.4 litres of hydrogen.
Q7. What is the molarity of a solution containing 5.85 g of NaCl(s) in a 500 mL solution?
Answer: Given
Mass of solute = 5.85 g
Volume of solution 500 ml
Molar mass of NaCl = 23 + 35.5 = 58.5
No. of moles of solute = Mass of solute / Molar mass of solute
No. of moles of solute = 5.85 / 58.5
No. of moles of solute = 0.1
Molarity = No. of the mole of solute / Volume of solution
Molarity = 0.1 / 0.5 = 0.2 mol / L
Q8. What is the mass of one atom of C-12 (in grams)?
Answer: Mass of 1 mole of C-12 atoms = 12 g
1 mole of C-12 atoms contains 6.022 × 1023 atoms.
Thus, the mass of one atom of C-12 will be = 12 / (6.022 × 1023).
Mass of one atom of C-12 = 1.99 X 10-23 g
Q9. What is the law of multiple proportions?
Answer: Law of multiple proportions was given by English chemist John Dalton. He states that when two elements combine to form one or more compounds. Then the weight of one element that combines with the fixed weight of other elements is in the small whole-number ratio.
Q10. What are the postulates of dalton’s atomic theory?
Answer: The postulates of dalton’s atomic theory are mentioned below.
He states that the atom is indivisible, i.e. we can not further subdivide it.
He states that all atoms of the same element are identical.
He states that different elements have different types of atoms.
Compounds are formed when atoms of different elements join in a simple whole-number ratio.
Q11. What are the demerits of dalton’s atomic theory?
Answer: The demerits of dalton’s atomic theory are mentioned below.
He states that an atom is indivisible, but we can further sub-divide the atom into electron protons and neutrons.
He states that atoms of different elements combine in a simple whole-number ratio, but this concept failed to explain sugar molecule combination (C12H22O11).
He failed to explain the existence of isotopes, isobars and allotropes.
Q12. Match the following.
Column I
Column II
1 mol of any gas
3 mol
88 g of CO₂
1 mol
5.6 litres of O2 at STP
0.25 mol
6.022 x 1023 molecules of H2O
2 mol
96 g of O
6.022 X 1023 molecules
Answer:
Column I
Column II
1 mol of any gas
6.022 X 1023 molecules
88 g of CO₂
2 mol
5.6 litres of O2 at STP
0.25 mol
6.022 x 1023 molecules of H2O
1 mol
96 g of O
3 mol
Q13. What are the differences between molarity and molality?
Answer:
S. No.
Molarity
Normality
1.
Molarity is the number of moles of compound present in 1 litre of solution.
Molality is the number of moles of solute present in 1 kilogram of a solvent.
2.
Its unit is mol / L.
Its unit is mol / kg.
3.
It is dependent on the temperature, volume and solubility of the solute.
It depends on the mass and is independent of temperature and volume.
Q14. What are the differences between molarity and normality?
Answer:
S. No.
Molarity
Normality
1.
Molarity is the number of moles of compound present in 1 litre of solution.
Normality is the gram equivalent of solute present in 1 litre of solution.
2.
Its unit is mol / L.
Its unit is eq / L or meq / L.
3.
It does not depend on the type of reaction the solute undergoes.
It depends on the kind of reaction the solute undergoes.
4.
It is dependent on the temperature, volume and solubility of the solute.
It is dependent on reactive species present in the solution.
Q15. Match the following physical quantities with their corresponding units.
Column I
Column II
Luminous intensity
mol / L
Mole
kg
Pressure
Unitless
Mole fraction
Pascal
Mass
mol
Molarity
Candela
Answer:
Column I
Column II
Luminous intensity
Candela
Mole
mol
Pressure
Pascal
Mole fraction
Unitless
Mass
kg
Molarity
mol / L
Practise Questions on Some basic concepts of Chemistry
Q1. What are the rules for writing significant figures?
Q2. If 4 litres of water are added to 2 litres of 6M hydrochloric acid solution. What will be the change in the molarity of the solution?
Q3. How much lime would be obtained by heating 200 kg of 95% limestone?
Q4. If a 500 mL 5 M solution is diluted to 1500 mL, what will be the molarity of the final solution?
Q5. The molar mass and empirical formula of a compound are CH2O and 180g. What will be its molecular formula?
