## Help with empirical and molecular formulas

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### Help with empirical and molecular formulas

1. An organic compound was found to contain 62.07% carbon, 10.34% hydrogen, and 27.59% oxygen. Determine its empirical formula and suggest a few possible molecular formulas. Name each of them. Do not consider ones that have more than 6 carbons.

2. A compound was found to have a molar mass of 245.8g and the following composition: 19.53% C, 2.44% H, 13.02%O, and 65.01% Br. Derive the empirical formula and its molecular formula.

3. A compound was found to contain 35.6% S, 11.1% H, and 53.3% C. Determine its empirical formula and suggest its molecular formula, knowing that it smells like rotten eggs when it becomes moist. Explain reasoning.
AmandaRayne123

Posts: 1
Joined: Tue Sep 01, 2009 7:58 pm

What math class generated these exercises? What mathematical methods are you supposed to use to answer these questions? (They read like chemistry questions, which is probably why I'm confused. )

When you reply, please include a clear listing of your work and reasoning so far. Thank you!

stapel_eliz

Posts: 1802
Joined: Mon Dec 08, 2008 4:22 pm

### Re: Help with empirical and molecular formulas

These are chemistry questions and not generally "math" questions. Assuming you already know about avagadro's constant (the mole) this information should help. I found it at http://www.ausetute.com.au/empirical.html

Calculating Empirical Formula from Percentage Composition

Assume 100g of sample

Convert all percentages to a mass in grams, eg, 21% = 21g, 9% = 9g

Find the relative atomic mass (r.a.m) of each element present using the Periodic Table

Calculate the moles of each element present: n = mass ÷ r.a.m

Divide the moles of each element by the smallest of these to get a mole ratio

If the numbers in the mole ratio are all whole numbers (integers) convert this to an empirical formula

If the numbers in the mole ratio are NOT whole numbers, you will need to further manipulate these until the mole ratio is a ratio of whole numbers (integers) .
more at http://www.ausetute.com.au/empirical.html.

good luck with finding your answers and I hope that this helps.
oonwa

Posts: 1
Joined: Tue Oct 13, 2009 12:29 am