What mass of nitrogen, N₂, will contain the same number of molecules as 1.8 g of water, H₂O? (Atomic masses : N = 14 u ; H = 1 u ; O = 16 u)

Mass of water = 1.8g

Equal moles of all substances contain an equal number of molecules

(1 mole of all substances contains 6.022 × 10²³ molecules).

To convert 1.8g  water into moles.

1 mole of water = (2 × 1) + (1 × 16) = 18g

18g water = 1 mole

1.8g  water = 0.1 moles

As equal moles of all substances contain an equal number of molecules, 0.1 moles of water will have the same number of molecules as present in 0.1 moles of nitrogen.

To find the mass of 0.1 moles of nitrogen in grams.

1 mole of nitrogen = 28g

0.1 moles of nitrogen     = 28 × 0.1 = 2.8g