Calculate the number of molecules in one kg of NaOH.
Mass of 1 mole of NaOH = Na + O + H = 23 + 16 + 1 = 40 g
40 g of NaOH contains 6.022 × 1023 molecules
∴ 1000 g of NaOH contains = 6.022×1023×100040\dfrac{6.022 \times 10^{23} \times 1000}{40}406.022×1023×1000
= 1.5 × 1025 molecules