Hydrogen burns in oxygen to make water: 2H2 + O2 gives 2H2O. What mass of water forms from 4 g of hydrogen? (H = 1, O = 16)

Answer and explanation

Correct answer: B. 36 g

  1. Step 1: Moles of H2 = 4 / 2 = 2 mol. The equation gives 2 mol of water for 2 mol of H2. Step 2. Mass of water = 2 x 18 = 36 g. Answer: 36 g. Why not the others: 18 g is one mole; 32 g is the oxygen mass; 72 g doubles the coefficient twice.

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