Question in the description, can you please explain how you got the answer, thank you

Question

What is the empirical formula for the following molecular formulas?

1). C₆H₁₂O₂₂ ___________________ 2). Fe₂O₃ ___________________ 3). C₂H₂ ___________________

Answer 1

Hi, Aaron,

The empirical formula for any compound is the lowest whole number ratio of atoms in a given compound. So, let's look at your three molecular formulas:

1) C₆H₁₂O₂₂ - for any compound, to determine the empirical formula, start by dividing each elements "quantity" by the smallest formula value. In this case, that number is 6 (which is the smallest of 6, 12, and 22), so we obtain: C₆ ÷ 6 = C₁

H₁₂ ÷ 6 = H₂

and O₂₂ ÷ 6 = O_3.67

But, remember, an empirical formula is only valid with whole number ratios ... and 3.67 isn't a whole number!! To fix this, it is helpful to recognize that 3.67 is also 3 2/3, which is the same as 11/3. If we multiply each of those above values by 3, we'll obtain C₃H₆O₁₁, which is the empirical formula for this compound.

2) Fe₂O₃: if we even start to divide 2 by 2 and then 3 by 2, we'll quickly see that we have already violated our whole number rule for empirical formulas. In this example, the empirical formula for Fe₂O₃ is Fe₂O₃!

3) C₂H₂ ... now that you've seen the first examples, do you think you can do this one, Aaron? I'm thinking you can, so I'll leave this for you "to" work out (oh, major hint there!).

Good luck,

Chris