A mixture of C3H8 and C2H2 has a mass of 2.8 g. It is burned in excess O2 to form a mixture of water and carbon dioxide that contains 1.6 times as many moles of CO2 as of water.

Find the mass of C2H2 in the original mixture. Express your answer to two significant figures and include the appropriate units.

The mass of C2H2 in the mixture is 0.56gram using the ratio of carbon in the products contributed by the C2H2.

Explanation:

The balanced equation for the reaction is: C3H8 + 2C2H2 + 10O2 >> 7CO2 + 6H2O.

From the reaction, we know that the oxygen was in excess, this will make the Carbon sources the limiting agents in the reaction. The details of the reaction showed that the ratio of water to the carbon dioxide is 1.6:1. This also means that the expected mole of carbon dioxide will be 7/1.6, which is 3.75moles.

The individual balanced equation of reaction is:

C3H3 + 5O2 >> 3CO2 + 4H2O

and 2C2H2 + 5O2 >>4CO2 + 2H2O. From this one can quickly tell that the propane is in sufficient supply as it produces 3 moles of CO2 out of the expected 3.75 moles obtained above. Leaving 0.75moles of CO2 to the ethyne.

The mass of ethyne in the mixture will therefore be: 0.75/3.75 X 2.8 = 0.56g.