Question

If 3.50 g of the unknown compound contained 0.117 mol of C and 0.233 mol of H, how many moles of oxygen, O, were in the sample? Express your answer to three significant figures and include the appropriate units.

Answer 1

Answer:

0.116 g.

Explanation:

• Firstly, we can find the mass of C and H in the unknown compound:

mass of C = (no. of moles of C)(atomic mass of C) = (0.117 mol)(12.01 g/mol) = 1.405 g.

mass of H = (no. of moles of H)(atomic mass of H) = (0.233 mol)(1.01 g/mol) = 0.235 g.

∴ mass of O = mass of unknown sample - (mass of C + mass of H) = 3.50 g - (1.405 g + 0.235) = 1.86 g.

∴ no. of moles of O = (mass of O)/(atomic mass of O) = (1.86 g)/(16.0 g/mol) = 0.116 g.