Dec 08 2010 - Quiz

We had quiz on percentage composition, empirical formula and molecular formula.

Decemeber 3, 2010

Today we learned how to :

Calculate the Empirical Formula! (organic compounds)

REMINDER! QUIZ on Empirical Formula, Percentage Composition

-Empirical Formulas including organic compound

-burning the compound (react it with O2)

-collecting and weighing of the products resulting from the burning of the compound

-from the mass of the products, the moles of each element in the original organic compound can be calculated

Eg. What is the EF of a compound when 5.0g sample is burned producing 15.0g of CO2 and 8.18g of H20.

Mol CO2 = 15g x (1mol/44.0g) = 0.341 moles

Mol H2O = 8.18g x (1 mol/18.02g) = 0.454 moles

Mol C = 0.431 moles because there is only 1 C in ( CO2) = 0.341 moles | 1.0 | 3

| |
Mol H = O.454 moles x 2 because there is 2 H in (H2O) = 0.908 moles | 2.6 | 8

EF = C3H8

0.341 moles of C x ( 12.0g/1 mol ) = 4.092g of C

0.908 moles of H x ( 1.0g/ 1 mol ) = 0.908g of H

Total Mass = (C) + (H) should equal to 5

so if the final answer equals the amount given in the question, you can reassure that there are not O in the EF.

Another Perfect example and step by step procedures!

http://www.ausetute.com.au/empirical.html

http://www.tutorvista.com/content/chemistry/chemistry-iii/organic-compounds/molecular-formulae.php

A good video explaining how to calculate the Empirical Formula

December 1 2010 - Empirical and Molecular Formulas

Happy December ~ ! Only about 2 more weeks until it's winter break. (:

So we learned about the empirical formula and the molecular formula. What exactly are they?

The empirical formula is a formula used to shrink down the ration of atoms (or moles) in a formula. All ionic compounds are empirical formulas!

For example, C4H10, which is butane in its molecular formula, would be C2H5 in its empirical formula.

The molecular formula is the form of the empirical formula showing the actual number of atoms that combine to form a molecule.

To calculate the molecular formula, you use this equation :

n = molar mass of the compound / molar mass of the empirical formula