posted by Cool Dom on .
4.A compund is found to have(by mass)48.38% carbon,8.12% hydrogen and the rest oxygen.(What % is missing to make the sum 100 %?) That is,figure % oxygen.What is its empirical formula?
Take a 100 g sample which will give you
43.38 g Carbon
8.12 g hydrogen
and 100-43.38-8.12 = g oxygen.
Now convert each of the grams to moles.
43.38 g/atomic mass C = moles C.
8.12 g/atomic mass H = moles H.
g oxygen/atomic mass O = moles O.
Now find the ratio of these moles to each other. The easiest way to do this is to divide the smallest number by itself (which of course will give you 1.000), then divide the other number of moles of the other elements by that same small number. The result should be values that are very close to whole numbers. Round them to whole numbers and those are the subscripts for the molecule. Note: Do not round too much; e.g. round 1.05 to 1.00 and 2.15 to 2.00 but 1.5 or 1.4 or 1.6 are rounded to 1.5 (because then you multiply everything by 2 to get rid of the 1/2) and the other numbers become whole numbers, usually, too. Post your work if you get stuck.