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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: DNAngel on March 14, 2011, 11:11:16 am

Title: Question about determining the empirical formula of a compound
Post by: DNAngel on March 14, 2011, 11:11:16 am

This is a question from the Heinemann Chemistry 2 textbook, and it goes like this:

When 0.100g of white phosphorus is burned in oxygen, 0.228g of an oxide of phosphorus is produced. The molar mass of the oxide is 284 gmol^-1.

a) Determine the empirical formula of the phosphorus oxide

b) Determine the molecular formula of the phosphorus oxide

Yeah, so my main trouble is writing out the equation and solving for the unknown mole ratios of the phosphorus oxide.

Title: Re: Question about determining the empirical formula of a compound
Post by: cltf on March 14, 2011, 11:50:52 am

first we set the equation out this way:

P_x + KO₂ --> P_xO_k2

Now we started off with 0.1g of phosphorus, and 0.228g of product was producted. That means that the unaccounted 0.128g must be the collective mass of the oxygen. therefore the ratio is:
0.100:0.128
then using the standard empirical formula methods divide by the respective molecular mass so P =30.97 and O₂ =32 (or 16 if you choose to ignore the "2" in the equation)

and you get 0.003228:0.004 or 0.008
divide by the smallest
1:1.24 (or 2.5) multiple the ratios till you get a whole number ratio in this case it is 4 (or 2)

4:5 (or 2:5)

so sub the values back into the questions

Title: Re: Question about determining the empirical formula of a compound
Post by: DNAngel on March 14, 2011, 01:20:57 pm

Thank you very much. It was a very helpful explanation and I managed to get the correct answer too  ;D