Magnesium Oxide Lab

Hey everyone! Today was a really fun day in chemistry because we did the Magnesium Oxide Lab.

At the beginning of class, Mr Lieberman checked in our pre-labs (don't forget that means a data table as well) and we got started on the Magnesium Oxide Lab. We began by massing an empty crucible and lid, and then massing the crucible, lid, and a 25 cm magnesium ribbon together. We recorded these two values in our data tables and then proceeded to place the covered crucible on the clay triangle. We lit the burner and removed the lid every three minutes for a total of fifteen minutes. After the flame had been carefully turned off and the crucible cooled down, we massed the crucible, crucible lid, and magnesium oxide product.

For the post lab:
1. we are first asked to calculate the mass of the magnesium metal and the mass of the product, using the law of conservation of mass to calculate the mass of oxygen that combined with the magnesium. (Law of conservation mass: the mass of substances in a closed system will remain constant, no matter what processes are acting inside the system). This should be done by subtracting the mass of crucible, lid, and ribbon from the mass of the crucible, lid, and magnesium oxide.
2.Then, we are asked to calculate the percent composition of magnesium oxide. To do this, start by calculating the formula mass, and dividing each component mass by the formula mass and multiply by 100.
3. We are then asked to use molar mass to calculate the number of moles for each reactant. (see class notes)
4. calculate the ration between the number of moles of magnesium to the number of moles of oxygen and find the empirical formula of magnesium oxide. Look at Elim's post if you still need help with empirical formulas!
5. convert mass to moles to find theoretical yield (this shouldn't be too complicated)
6. calculate your percent yeild

Hope this helps! Tonight's homework is to complete Avagadro's Crash Activity. If you still need help on empirical formulas I found the following video very helpful http://www.youtube.com/watch?v=r2Log6-voWo! Also, work on the lab (due Thursday), and don't forget to begin studying for Thursday's test! Tomorrow's scribe is Katie I!

Empirical vs Molecular Formula

Today, we started class by getting back our quizes from last week.  I didn't take the quiz so I have no idea what happened in the beginning of the class.  I am sorry~  Anyway we went over the quiz about 15 minutes.
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 %.
 - 71.65% (Cl)
 - 24.27% (C)
 - 4.07% (H)
The molar mass is known to be 98.96g/moles

First, assume a 100g of the sample
 - 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

Hydrate Lab Day!

We started class with finishing the back sides of our quizzes for 10 minutes. Then we started the pre-lab for the Hydrate Lab we did in class. We first discussed three rules to follow when operating a Bunsen Burner. The first rule is to not leave it on unattended, do not touch it while hot, and keep all hair tied back and loose sleeves out of the way. The next question we discussed was to find:

a. The mass of the hydrate

b.the mass of the water lost during heating

c. the percent water in the hydrate

We were given the mass of:

Empty Test Tube: 18.42 grams

Test Tube and Hydrate (before heating): 20.75 grams

Test Tube and Anhydrous Salt (after heating): 20.41 grams

To calculate these you had to:

a. 20.75 g -18.42 g= 2.33 g

b. 20.75g- 20.41 g =.34g

c. .34g/2.33g=14.59% (round for significant figures)=15%

After this question you had to complete the table given on the Hydrate Lab sheet.After this, we got together with our lab groups and began the Hydrate Lab here are the steps:

1. We took the mass of the pyrex test tube.
2. We added around 2grams of blue hydrated (with water) copper (II) sulfate.
3. We then massed the test tube with the copper (II) sulfate in it.
4. We then set up the clamp and tilted the tube slightly down so the evaporating water can leave the test tube.
5. Then then focused the heat from the Bunsen burner on the copper (II) sulfate and heated it evenly until it turned white. We tried to avoid burning it. (turned brown if burned)
6. Then we wiped out the excess water droplets and massed the tube with the anhydrous salt.

So that was our Hydrate Lab! The next scribe is... Ellen Hirsch!!

This was Korri Hershenhouse! Don't forget to do your How Much Are You Worth Project for monday! Also don't forget to complete the webassign and do the post lab also for monday!