The number of atoms in 8g of sodium is x × 10²³. The value of x is ____________. (Nearest integer)
[Given : N A = 6.02 × 10²³ mol⁻¹
Atomic mass of Na = 23.0 u]

Solution

Chemistry ma’am · 3 steps

Grams to moles first, then moles to atoms: divide by 23, then multiply by Avogadro's number.

1. Moles of sodium. The molar mass of Na is 23.0 g mol⁻¹, so 8 g is 8/23 = 0.348 mol.

   N = m/M × N_A = 8/23 × 6.02 × 10²³

2. Put in numbers. 8 × 6.02 = 48.16, and 48.16/23 = 2.09. So N = 2.09 × 10²³ atoms.
3. So. x = 2.09, which rounds to 2.

The common slip: 48. Multiplying 8 by 6.02 × 10²³ without dividing by the molar mass treats 8 g as 8 mol and gives 48, not 2.

The idea to keep. Mass never goes straight to particles. Always pass through moles: divide by molar mass, then multiply by N_A.

Answer from the NTA final answer key. Solution by PrepWiser.