Today we started off class by turning in our Solution Formation lab. (Mr. Lieberman also wants to know where his door stopper is...if anyone knows or finds it)
The rest of class was working on our new Solubility Curve lab (due Monday).
This took up the whole classtime and we even had to split up the work amongst our groups to get the job done faster. Essentially, we had two "series" to run, each with the same procedures but with different masses for the materials in the three test tubes.
In the first session, test tube A had to contain 0.45 to 0.50 grams of potassium nitrate (KNO3), test tube B had 0.70 to 0.80 grams, and C had to have 1.20 to 1.30 grams.
I massed each of these tubes and then with the KNO3. Then I massed each test tube with water added. From there, I placed each test tube into boiling water and stirred them gently (well actually, prodded at them more) to make the KNO3 dissolve faster. Once it was completely dissolved, I first took out test tube C and placed it in a beaker of iced water to make it crystallize. The temperature at which test tube C started turning white was recorded. This is the same as the saturation temperature. What was done to test tube C was then done for the other test tubes.
The second series (that was being tested at the same time) had test tube A massed at 0.35 to 0.40 grams, B with 0.90 to 1.00 grams and C with 1.50 to 1.60 grams. My partners then repeated the process I explained above.
<------(crystallized KNO3)
There are some calculations and a graph to do on the computer to go with this lab, along with the conclusion.
(There is also a Webassign due at 1:00 Friday.. just in case)
The next scribe will be.....Austin W.
Today, as we walked through the door, we picked up two sheets from Mr. Lieberman's desk:
A brand new notes sheet and a worksheet for homework to go with it.
The lesson for the day was all about ENERGY and where it gets distributed during a reaction. The reaction itself is called a system, which is what we look at for data. The surroundings are made up of everything else in the environment outside the system.
-There are then three types of systems that we went over quickly
-Open system: can exchange matter AND energy with the surroundings (ex: open beaker)
-Closed system: can exchange ONLY energy with the surroundings while matter remains fixed (ex: sealed flask) -Isolated system: can't exchange energy or matter with its surroundings (ex: thermos)
Then there's the exothermic and endothermic reactions. Exothermic is when energy flows OUT of a reaction due to temperature difference in the system and surrounding (negative q). Endothermic is when energy flows INTO a system from the surroundings (positive q).*Qsurroundings = -Qsystem* They are equal and opposite for distribution of heat/energy
these are graphs like the ones we made in class:
(the activation energy is the energy to start the reaction)
After notes, we did a mini lab called Heat of Fusion of Ice with our partners.Each group got a 100 ml beaker which we needed to mass before putting ice in it and massing it with the ice. My partner, Kathryn, then got warm water from Mr. Lieberman which measured to be about 71 ml with our data.
The initial water temperature was 50.6 degrees C and the final temperature with the water and melted ice was 22.6 degrees C.
After finishing the procedure, we were assigned to find the molar heat of fusion of ice using ratio. Before that, however, you need to determine the MOLES of ice that were melted.
(this will be due friday, while we have a webassign due tomorrow with a lab and another webassign due friday. whew..)
The next scribe will be...Rebecca N.
Well, maybe it's not exactly fun, but today class was all about the numbers in chemistry. More specifically, Sig Figs, or Significant Figures.
To start things off, we first went over the Metrics worksheet we had for homework. (Some new metric measurements that were not in the notes was hectogram (hg) which is equal to 100 grams, and cm^3 = 1 ml) One of the things we checked checked for was estimating past the last readable digit, meaning if the last digit of a measurements is in tens, then you would estimate to ones to leave room for error.
On a bit of a side note, the last problem on the worksheet showed an illustration of a buret, which appears to be measuring upside-down, but is in fact correctly labeled. Mr. Lieberman told the class that we would be using this instrument a lot in second semester.
(I added the picture simply because of the lack of color....and for a visual of course..)
For the rest of class, we got another worksheet (for homework) and went over notes for sig figs and scientific notation, which is, as most of us already know, something like 590000 to 5.9 x 10^5 to show the number of significant numbers.
However there are also some rules to sig figs that play into measurements and the scientific notation. For precision's sake, these rules are:
-nonzero integers count as sigfigs
-leading zeros are never significant (0.000757 has 3 sig figs)
-captive zeros always count as significant figures (such as in 16.07, there are 4 sig figs)
-trailing zeros are only significant if the number contains a decimal point (9.300 has 4 sig figs. If the number were 500, there is only one sig fig, unless it was written as 500.0.)
For mathematical operations, there are different rules for adding/subtracting and multiplying/dividing:
Adding/subtracting : the # of sig figs in the result equals the number of decimal places in the least precise measurement.
EX: 6.8 + 11.938 = 18.734, which turns into 18.7 (for 3 sig figs)
Multiplying/dividing : the # of sig figs in the result equals the number in the least precise measurement used in the calculation.
EX: 6.38 x 2.0 = 12.76, which becomes 13 (2 sig figs)
(All of these notes can be found on the powerpoint)
And with a schedule that was shifted around, we ended class in 40.0 minutes.
As a reminder, we have a quiz on the measurements and sig figs we went over tomorrow. The quiz Mr. Lieberman assured would not be as easy as our first quiz.. Good luck to us all..
and the chosen one to be scribe tomorrow will be... Zoe S.
