Question

An unknown compound contains only carbon, hydrogen, and oxygen (CxHyOz). Combustion of 7.00 g of this compound produced 10.3 g of carbon dioxide and 4.20 g of water.

Part A

How many moles of carbon, C, were in the original sample?

Express your answer to three significant figures and include the appropriate units.

Part B

How many moles of hydrogen, H, were in the original sample?

Express your answer to three significant figures and include the appropriate units.

Answer 1

PART A

The reaction would then be CxHyOz + ?O2 -----> ?CO2 + ? H2O

You know the mass of the compound = 7.00g

You know the mass of the CO2 = 10.3 g

You know the mass of the H2O = 4.20 g

Using the conservation of mass law you should have 10.3+4.20-7.00 g of O2 as a reactant. That is

7.5 g of O2.

moles=mass/molar mass.

moles C in the original sample = 10.3/44.009 g/mol=0.234

PART B

The reaction would then be CxHyOz + ?O2 -----> ?CO2 + ? H2O

You know the mass of the compound = 7.00g

You know the mass of the CO2 = 10.3 g

You know the mass of the H2O = 4.20 g

Using the conservation of mass law you should have 10.3+4.20-7.00 g of O2 as a reactant. That is

7.5 g of O2.

moles H = 2 x 4.20/18.02 g/mol= 0.466