Questions Based on Mole Concept
CBSE Class 9 Chemistry
Q1: Fill in the blank.
The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly ________ of C₁₂
Answer: 12g or 12 grams.
Q2: I owe you 1 mole of rupees. How many rupees do I have to pay for you?
Answer: 6.022 × 10²³ rupees.
Q3: Is mole a unit?
Answer: No, it is a large constant number called Avagadro's constant (N) = 6.022 × 10²³
Q4: Atomic mass of Na is 23u. What is the mass of 1 mole of Na atoms? Is there any name for this?
Answer: 23g. It is also called the molar mass of Na atoms.
Q5: Atomic mass of oxygen(O) is 16u. What's its molar mass?
Answer: 16g.
Q6: What is the molecular mass of Water molecule (H₂O)?
Answer: Atomic mass of H = 1u
The atomic mass of O = 16u
The molecular mass of H₂O = mass of 2 atoms of H + mass of 1 atom of O
= 2 × 1u + 16u
= 18u
Q7: What is the molar or gram molecular mass of water?
Answer: Molecular mass of Water (H₂O) = 18u
Gram molecular mass = 18g or 18 grams
Q8: How many moles will be in 45g of water(H₂O)?
Answer: Molecular mass of H₂O = 18u
Mass of 1 mole of H₂O = 18g
No. of moles in 45g of H₂O = 45 ÷ 18 = 2.5 moles
Q9: How many atoms of Hydrogen are there in 2 moles of water?
Answer: 1 molecule of H₂O has H-atoms = 2 atoms
1 mole of H₂O has H-atoms = 2-mole atoms
2 moles of H₂O has H-atoms = 2 × 2 = 4 moles of atoms
= 4 × 6.022 × 10²³
= 24.088 × 10²³
= 2.4088 × 10²⁴ H-atoms
Q10: How many grams of SiO₂ are present in 0.8 mol? (molecular mass of SiO₂ = 60.1u)
Answer: Molecular mass of SiO₂ = 60.1u
1 mole of SiO₂ = 60.1g
0.8 mol of SiO₂ = 60.1 × 0.8 = 48.1g
Q11: Under standard temperature pressure conditions, what is the volume of 1 mol of gas?
Answer: 22.4 litres or 22.4l
Q12: How many mol of CO₂ (carbon dioxide) are present in 55.5 L ?
Answer: 1 mol of CO₂ = 22.4 l
55.5 litres contains = 55.5/22.4
= 2.48 mol of CO₂
Q13: What will be the mass of 12.044 × 10²³ molecules of O₂?
Answer: Molecular mass of O₂ = 2 × 16u = 32u
∴ 1 mol of O₂ = 32g
⇒ 6.022 × 10²³ O₂ molecules have mass = 32g
12.044 × 10²³ molecules of O₂ = 32 × 12.044 × 10²³ / (6.022 × 10²³)
= 32 × 2
= 64g
Q14: Calculate the mass of glucose in 2 × 10²⁴ molecules. Molecular mass glucouse is 180u
Answer: Molecular mass of glucouse = 180u
Gram molecular mass of glucouse = 180g
⇒ 1 mole (6.022 × 10²³) molecules = 180g
2 × 10²⁴ molecules will have mass = 180 × 2 × 10²⁴ / (6.022 × 10²³)
= 180 × 2 × 10 / 6.022 = 597.7 g
Q15: Write formula to calculate Number of moles
(a) of monoatomic substance, if its mass is given
(b) of a molecular substance, if its mass is given
(c) of a monoatomic substance, if number of atoms are given
(d) of a molecular substance, if number of molecules are given
Answer:
(a)
| No. of moles = | mass |
| atomic mass |
(b)
| No. of moles = | mass |
| molecular mass |
(c)
| No. of moles = | no. of atoms |
| 6.022 × 10²³ |
(d)
| No. of moles = | no. of molecules |
| 6.022 × 10²³ |
