posted by Mark .
What is the empirical formula of a hydrocarbon that contains 89.94% C by mass?
100-89.94 = %H.
Take a 100 g sample which will give you the percent in grams.
Convert grams to moles. moles = g/atomic mass.
Then find the ratio of the elements to each other with 1.00 being the lowest. The easy way to do that is to divide the smaller number by itself (which assures that number of being 1.000), then divide the other number by the same small number and round to whole numbers (but don't round too much. See note:) This is the empirical formula.
Note: If the number is close to q whole number (1.06 2.1 2.9, etc round it. If it is further away, such as 1.24 1.33, etc, multiply by whole numbers until you find values for both that can be rounded to whole numbers. For example, 1.00 and 1.33 could be multiplied by 3 to obtain 3 and 3.99 which can be rounded to 3 and 4.)
C7H10 is not an option.