# Chemistry

What is the empirical formula of a hydrocarbon that contains 89.94% C by mass?

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1. 89.94%C, then
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.)

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2. c7h10

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3. C7H10 is not an option.

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So basically what you would do is you world take the 89.94 and divide that by the mass of carbon (and I am just going to round) and that would be 89.94/12=7.495 (I'll round that to 7.5). Then you would subtract 100-89.94 and you're going to subtract by 100 because we are dealing with percent, and percent is ALWAYS out of 100%. So after subtracting you're going to get 10.06 for hydrogen. The mass for hydrogen is 1, so then you'll divide 10.06/1 and the answer is going to be 10.06.
Example: C= 89.94/12 = 7.495----> 7.5
H= 10.06/1 = 10.06 ----> 10.1

You then take the smallest ANSWER you got out of Carbon and Hydrogen. Which is 7.5 from carbon and divide EACH answer.
Example: C= 89.94/12 = 7.495----> 7.5 7.5/7.5 =1
H= 10.06/1 = 10.06 ----> 10.1 10.1/7.5 =1.34---> round to 1.3

Like what one of the previous people stated. You can only round the answer for the empirical formula if its like 3.9 to 4, 5.01 to 5, 2.1 to 2. So, our answer is 1.3 and we can't round it and you can't leave the answer as a decimal.
Example:
Our answer is going to be from 1.3 to 1 1/3 (a mixed fraction).

To get rid of the mixed fraction you're going to multiply 3 (denominator of fraction) from each side.
Example:
(3)1 1/3(3) now the 3 is going to cross out each other from the denominator and you're going to multiply the 3 to the 1 (WHOLE NUMBER of the fraction)

so then, you'll get 3x1= 3, and since the 3 from the denominator of the fraction cancelled out you're only going to get a 1 from the numerator. After, you'll add the number you multiplied and the numerator together.
Example:
product of the 3x1 =3 and what's left of the fraction a.k.a the numerator =1
3+1=4
Since, now we have a whole number 4 will be the answer for hydrogen. H4!

Now, go back to when we had the mixed fraction

1 1/3 and we had to multiply by 3 on each side.
Remember we had to multiply by 3 to cancel out the denominator

The 3 (a.k.a the multiplier) is now going to be your NEW answer for 3.

C3H4

*I hope you could understand everything, I know the notes are long, but its hard to type this instead of writing it. I also hope that everything was actually useful and helpful.
Goodluck!

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