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Combustion Analysis. P. Perkerson. A little reminder!.
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Combustion Analysis P. Perkerson
A little reminder! • You have learned previously that during combustion reactions some type of fuel is burned and water and carbon dioxide are the products. Sometimes the fuel is a hydrocarbon (contains only carbon and hydrogen) and sometimes there are other components to the fuel. • Ex. Methane combusts in the presence of oxygen • CH4 +2O2 CO2 + 2H2O • Methanol combusts in the presence of oxygen • 2CH3OH+3O2 2CO2+ 4H2O
Finding the empirical formula of a fuel • If given the components of the fuel, mass of original substance, mass of products (water and carbon dioxide) we can determine the empirical formula. If given the molecular mass of the original substance, we can also determine the molecular formula. However, this only works if combustion is complete – meaning that all of the fuel is consumed in the reaction.
Let’s do an example! • Combustion of 0.255 grams of isopropyl (a fuel composed of C,H, & O) produces 0.561 g CO2, 0.306 g H2O • Step 1: Find the grams of carbon • Step 2: Find the grams of hydrogen • Subtract the mass of the carbon & hydrogen from the original mass. That gives you the mass of the oxygen
Now that you have the masses for all three components, you can convert grams to moles, divide all by the small, etc.
Let’s try another! • What makes dirty socks so stinky? Caproic acid – composed of carbon, hydrogen and oxygen. A 0.225 g sample has 0.512 g CO2 and 0.209 g H2O • Find the mass of the carbon. • Find the mass of the hydrogen. • Find the mass of the oxygen.
Mass to moles: divide all by small to get the empirical formula
If the molecular mass of “stinky socks” is 116.01 grams per mole, what is the molecular formula?
You try this one on your own! • A 0.548 g sample of a fuel composed of carbon, hydrogen and nitrogen is completely combusted. 0.312 grams of water and 1.525 grams of carbon dioxide are produced. The molecular formula mass is 79.01 grams per mole. What are the empirical and molecular formulas?