Then we started to learn what empirical formula is, and how this Empirical formula relates with Molecular formula.
Molecular formula = (Empirical formula)n
* n is an integer
Once you get Empirical formula, then easy to get Molecular formula.
The Empirical formula is the simplest form of the Molecular formula.
For example :
Molecular formula - C6H12
Empirical formula - Divide by 6 - CH2
Here is a sample we did in the class:
Determine the Empirical and Molecular formulas for a compound that gives the following %.First, assume a 100g of the sample
- 71.65% (Cl)
- 24.27% (C)
- 4.07% (H)
The molar mass is known to be 98.96g/moles
- 71.65g (Cl)
- 24.27g (C)
- 4.07g (H)
Second, Convert gram to moles
- 71.65g x 1moles / 35.5g = 2.018 moles of Cl
- 24.27g x 1moles / 12g = 2.02 moles of C
- 4.07g x 1moles / 1g = 4.07 moles of H
Third, divide each moles by smallest number of moles
- Cl : 2.018 moles / 2.018 moles = 1 mole
- C : 2.02 moles / 2.018 moles = 1 mole
- H : 4.07 moles / 2.018 moles = 2 moles
Finally we can get the Empirical formula like this : CClH2
Now, we can find the molecular formula by finding the mass of the Empirical formula and setting up a ratio:
CClH2 → C2Cl2H4
*If you want more information about Empirical formula
I recommend you to visit http://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm
After we had finished the note, Mr. Liberman introduced an activity. This activity is called Crash of Avogadro Airlines Flight 1023.
The goal of this activity is finding a murderer.
On the first and second side of the sheet, there are 3 tables which help to find the horrible murderer.
In this activity each chemical can be used once or no time.
Tonight's homework is to finish the hydrate lab, do a Magnesium Oxide pre-lab and Avogadro Airline activity which is due on Wednesday.
Just a reminder, the unit 3 test is on Thursday.
The next scribe is Ellen Hirsch
