Hess's Law Lab

Hey everone! Friday was another interesting day in Chemistry. After everyone got seated, Mr. Lieberman talked to us about the days activity, which included a Hess's Law Lab. After going over the procedure, we got in our lab groups, put on our visorgogs, and got to work.

First, we made our date tables, which should ideally include two separate areas (for Equation A and Reaction #2) with spaces for two trials. We began Equation A by measureing two strips of magnesium ribbon and recording that in our data table. We then massed a clean dry calorimeter, and remassed it once we added 15 mL of HCl (recording both in the data table, of course). We took the initial temperature of the HCl, and then added a piece of magnesium to the calorimeter. We stirred the piece as it dissolved, and then retook the temperature once it was constant. Once that was over and we recorded all of those temperatures and masses in our data table, we repeated!

Then, it was on to Reaction #2. We remassed the calorimeter (once it was clean and dry), and remassed once we added 15 mL of HCl. To switch things up, we then added about .20 g of magnesium oxide. We recorded the masses of the calorimeter, as well as the actual mass of the magnesium oxide in our data table. Once we added the magnesium oxide in the calorimeter, we stirred until the temperature remained constant. We recorded this temperature and then repeated the whole process!

Once this lab was over, we left chemistry to go enjoy our weekends. Don't forget to work on this lab, though, it's due Tuesday! Good luck to Bobby S, our next scribe, on his first post for Period 6!

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!

Oleic Acid Lab and Bohr Notes

Today was another exciting day in chemistry! We started off by finishing off some of yesterday's notes.

Atomic history day #2 1

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We got even further into atoms this afternoon by learning about Niels Bohr. Bohr introduced the Bohr Model in 1913, that is still widely used today. He discovered that the neutrons and protons lie in the center of the atom, a dense region called the nucleus, while the electrons are free to orbit the nucleus. The electrons circle around the nucleus much like the planets revolve around the sun, yet they are not confined to a planar orbit.






After we finished the notes, Mr. Lieberman reviewed yesterday's Rutherford Experiment. He gave us the correct formulas for finding the area of the circles and squares on the sheet, which are

(% dots in circles) x 602 cm^2=area of six circles

(% dots in squares) x 602 cm^2= area of six squares



Then we began our Oleic Acid Lab. Prelabs were checked in, and then we got in our lab groups to begin this exciting lab. First, we filled a dropper with methonal and counted the drops it took to fill 1 mL. We used this information to calculate the volume of a single drop of methanol.



We than took a lunch tray, cleaned it with warm soap and water, and filled it with cool water about 0.3 cm deep. We applied a thin layer of lycopodium powder and added 2 drop of a .500% oleic acid solution. Once this is done, we were instructed to measure 8 different diameters of the cirlcle that was formed, and averaged the diameters.

We didn't get any farther in the lab, because of time constraints. Tonights homework is to work on the lab (which is due Friday), but Mr Leiberman warned us that the calculations are extremely difficult.

Don't forget to wear your togas tomorrow so the homecoming genie pays us a visit! And, tomorrow's scribe will be Katie I.

Learning About Rutherford

Yesterday was a very eventful day in Period 6 chemistry! We began class by once again summoning the homecoming genie (he didn't show up). Shortly after, we began with some notes on Ernest Rutherford.

A student of J.J. Thomson, Rutherford started noticing that "alpha" particles were sometimes deflected by something in the air, and he couldn't figure out why. So he began his gold-foil experiments. He fired alpha particles at an extremely thin sheet of gold foil, and discovered that they were deflected through large angles and could even be reflected strait back at the source. This showed that most of the atom was empty, and there was a dense positive area in the atom (the nucleus).

Atomic history day #2 1

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After the notes, we took part in an interesting Rutherford Simulation modeled after the experiments Rutherford did when he discovered the nucleus. We got into groups of two and received papers, marbles, and carbon paper. Each sheet of paper had six cirlces on it with a tiny square in the center of each circle. We laid a peice of carbon paper (face down) on top of this sheet and dropped a marble on the paper about 200 times. This left each group with a sheet with 200 black dots scattered throughout the circles, squares, and outside edges.

We were challenged to use this sheet (and the dots that marked it) it estimate measurements for the areas of the circles and squares. The correct way to do this was to do

(% dots in circles) x 602 cm^2=area of 6 circles, and the same for squares, just replacing the percentages.

The nights homework was to work on this expirement for Friday, Oleic Acid Prelab, and the Chemthink.