Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: What is the empirical formula of this compound thanks?

  1. Mar 25, 2008 #1
    A hydrated substance was found to have the following percentages composition:

    Na = 16.1%
    C = 4.2%
    O = 16.8%
    H2O = 62.9%

    What is the empirical formula of this compound?


    im really confused and dont know where to start so if someone could help itd be very much appreciated!

    thank you :)
  2. jcsd
  3. Mar 25, 2008 #2
    There's a post further down on the board that addresses a problem like this. I'll copy and paste MichealXY's poem that should help:

    Percent to mass,
    Mass to mole,
    Divide by small,
    Multiply 'til whole.

    Assume 100g of compound. Change % to g. Divide these masses by their molar masses to get moles. Divide each mole amount by the smallest mole quantity of the group. You'll get numbers that are either close to a whole number or close to half (such as 1.5, 2.5, etc.) multiply all of the numbers by a common factor until they are all whole numbers, and this will be the empirical formula.
  4. Mar 29, 2008 #3
    Yes what juicy said is correct. This is obviously going to be a hydrate so it might be a little tricky figuring it out for that part. Make sure that once you "think" you have the right answer, that you check it to make sure the percentages check out correctly.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook