A sample of mercury with a mass of 114.0g was combined with 12.8g of oxygen gas, and the resulting reaction gave 123.1g of mercury(II) oxide.

How much oxygen was left over after the reaction was complete?

Expert Answers

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The reaction can be written as,

                                  2Hg + O2 --> 2HgO

For the calculation the following molecular weights are considered.

Hg - 200.6 g/mol, O - 16 g/mol

according to the stoichiometric reaction, 401.2 g of Hg reacts with 32 g of O2 and produces 433.2 g of HgO

Hence the amount of O2 that will react with 114.0 g of Hg can be calculated as,

=> (114/401.2)x32

=> 9.1 g

Therefore the amount of excess O2 is = 12.8 g - 9.1 g

                                                       = 3.7 g

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