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Some basic concepts of Chemistry Questions

Chemistry tell us about the structure, composition and property of substances. It also tells us about the transformations substances undergo and the energy released or absorbed during these operations.

Definition: Chemistry is the branch of science that deals with molecules and their transformations. It tells us about the properties, composition, and structure of substances.

Some basic concepts of Chemistry Questions with Solutions

Q1. Which carbon isotope is used in obtaining relative atomic masses?

  1. Carbon-12
  2. Carbon-13
  3. Carbon-14
  4. None of the above

Answer: (a), The carbon-12 isotope is used to obtain relative atomic masses.

Q2. What is the relation between the molar mass and the vapour density of a gas?

  1. Molar mass = Vapour density / 2
  2. Molar mass = 2 × Vapour density
  3. Molar mass = Vapour density
  4. No relation

Answer: (b), Molar mass = 2 × Vapour density.

Q3. How many significant figures are there in 7070 × 107?

  1. Two
  2. Four
  3. Seven
  4. Can’t be determined

Answer: There are four significant figures in 7070 × 107.

Q4. What do you mean by the term significant figure?

Answer: Significant figures refers to the digits that carry a meaning towards the resolution of the measurement.

For example, 3600 has two significant figures. In contrast, 36.00 has four significant figures.

Q5. What is gay lussac’s law of combining volumes?

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?

  1. 22.4 litres
  2. 11.2 litres
  3. 1 litre
  4. 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?

Click the PDF to check the answers for Practice Questions.
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