Question
Sometimes, instead of percentages compostion, you will have the composition of a sample by mass. Using the actual mass of the sample, determine the empirical formula for compounds that have the following analyses.
A.
a .858g sample of an unkown substance is composed of .537g of Copper, and .321g of Florine
How would you do this problem? When doing empirical formula, I only know how to do it if its a percentage. Should I divide the amount of copper over the total of the unknown substance to get a percentage and then convert to moles? Help.
A.
a .858g sample of an unkown substance is composed of .537g of Copper, and .321g of Florine
How would you do this problem? When doing empirical formula, I only know how to do it if its a percentage. Should I divide the amount of copper over the total of the unknown substance to get a percentage and then convert to moles? Help.
Answers
DrBob222
That's exactly how you do it. First determine percent Cu, then percent fluorine. Let's just suppose these come out to be 70% and 30% (made up numbers). Then take a 100 g sample which will give you 70 g Cu and 30 g F. Find moles from that and convert to ratios.
Chopsticks
Hey, but how far should I round the percentage to?
DrBob222
You have three significant figures in each of the masses; I like to carry one extra place and round at the end when I do the ratios. That means carry the percentages to the hundredths place or two places to the right of the decimal.