Question

Among the following, choose the ones with an equal number of atoms.

1. 212 g of Na₂CO₃ (s) [molar mass = 106 g]
2. 248 g of NaNO₃ (s) [molar mass = 62 g]
3. 240 g of NaOH (s) [molar mass = 40 g]
4. 12 g of H₂ (g) [molar mass = 2 g]
5. 220 g of CO₂ (g) [molar mass = 44 g]

Choose the correct answer from the options given below:

• A. A, B, and D only
• B. B, C, and D only
• C. B, D, and E only
• D. A, B, and C only

Hint:

When comparing number of atoms in different compounds, first calculate the number of moles and then multiply by the number of atoms per mole.

Answer 1

The Correct Option is A

• A. 212 g of Na₂CO₃ (molar mass = 106 g/mol)

  • Moles = 212 g / 106 g/mol = 2 mol
  • Atoms per molecule = 2 (Na) + 1 (C) + 3 (O) = 6 atoms
  • Total "atoms" = 2 mol * 6 atoms/mol = 12

• B. 248 g of Na₂O (molar mass = 62 g/mol)

  • Moles = 248 g / 62 g/mol = 4 mol
  • Atoms per molecule = 2 (Na) + 1 (O) = 3 atoms
  • Total "atoms" = 4 mol * 3 atoms/mol = 12

• C. 240 g of NaOH (molar mass = 40 g/mol)

  • Moles = 240 g / 40 g/mol = 6 mol
  • Atoms per molecule = 1 (Na) + 1 (O) + 1 (H) = 3 atoms
  • Total "atoms" = 6 mol * 3 atoms/mol = 18

• D. 12 g of H₂ (molar mass = 2 g/mol)

  • Moles = 12 g / 2 g/mol = 6 mol
  • Atoms per molecule = 2 (H) = 2 atoms
  • Total "atoms" = 6 mol * 2 atoms/mol = 12

• E. 220 g of CO₂ (molar mass = 44 g/mol)

  • Moles = 220 g / 44 g/mol = 5 mol
  • Atoms per molecule = 1 (C) + 2 (O) = 3 atoms
  • Total "atoms" = 5 mol * 3 atoms/mol = 15

Now, we compare the total "atoms":

A = 12

B = 12

C = 18

D = 12

E = 15

A, B, and D have the same number of atoms (12).