Chapter 3: Atoms and Molecules- Exercise- 42

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Chapter 3: Atoms and Molecules

Class: IX

Exercise number 42

Question 1

If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?

Answer 1

Given, one mole of carbon atoms weighs 12g

i.e., mass of 1 mole of carbon atoms = 12g

Then, mass of 6.022× 10²³ carbon atoms = 12g

Therefore, mass of 1 atom of carbon = 12 / (6.022×1023 g)

= 1.9926 × 10^{– 23} g

Question 2

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23u, Fe =56 u)?

Answer 2

Given that, atomic mass of Na = 23u

Then, gram atomic mass of Na = 23g

Now, 23 g of Na contains = 6.022×10²³ atoms

Thus, 100g of Na contains = ( 6.022×10²³ ×100) / 23 atoms

= 2.6182 × 10²⁴ atoms

Again, given atomic mass of Fe = 56u

Then, gram atomic mass of Fe = 56g

Now, 56 g of Fe contains = 6.022×10²³atoms

Thus, 100 g of Fe (6.022×10²³ ×100) / 56 atoms

= 1.0753 × 1024 atoms

Therefore, number of atoms in 100 grams of sodium is more than 100 grams of iron.

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