Question

What mass of oxygen is needed for the complete combustion of 122 mL of

            C₆H₆  (molar mass = 78.1 g/mol) to produce carbon dioxide and water?

            Density of C₆H₆ = 0.88 g/mL

2C₆H₆(l) +   15O₂(g) 12CO₂(g)   +   6H₂O(l)

Answer 1

1.) 122 ml C6H6 * (0.88 g C6H6 / ml C6H6) = 138.6363 g C6H6 (approx. 139 g C6H6)

2.) Find Molecular weight of C6H6: Approx. 12*6+6=78g/mol

3.) 139 g C6H6 * (1 mol C6H6/78 g C6H6) = 1.7820 mol C6H6

4.) 1.7820 mol C6H6 * (15 mol O2 / 2 mol C6H6) = 13.365 mol O2

5.) Find molecular weight of O: approx. 32 g/mol

6.) 13.365 mol O2 * (32 g O2 / 1 mol O2) = 427.68 g oxygen

You should be able to combine ALL steps into one step using dimensional analysis.

427.68 grams oxygen is needed