Heating Curve Lab

    Welcome back!  Today was the first day of the second semester.  Besides getting new seats and some old work back, we also began a new lab.  If you don't have it you can find it here (however this format is slightly different).  We will no longer be using the pre-lab, data, post-lab format.  The new outline for our labs is:


Title:
Lab Goal:
Data/Collections:  (includes data, labeled graph, and percent error)
Conclusion:  (includes claim (according to your data...), evidence (what data did you use 
                   that helped you make this claim?  How did you identify what ever you were 
                   looking for), and reasoning (does your data make sense?  Why might it not be
                   what you expected it to be?)


    In the lab, we filled a 400 mL beaker with about 150 mL of snow/crushed ice.  The goal of the lab was to find out the temperature at which ice melts and boils (using the heating curve).  The next step was to take the initial temperature of the ice.  My group got about -.5º C (however you should turn this number to Kelvin [add 273] because when calculating the percent error it will be difficult to work with Celsius whose freezing point is 0º).  
    
    Next, the beaker was placed on a hot plate and the heat was turned on halfway.  The crushed ice was stirred and every minute it's temperature was taken.  After all the ice melted the hot plate was turned on to full value.  We continued to stir the liquid and take its temperature every minute.  The hot plate was turned off after 3 minutes of boiling (100º C).  


    The data you got (temperature and time of the the different phases of the ice) will now be used to make a graph (recall earlier this year when we used excel to make tables and graphs with curves/lines).  Instead of writing a post lab, you will write up a conclusion summarizing the lab and explaining at what temperature the ice melted and boiled at and why this is so.  


    That was about it for today.  This lab is due wednesday.  Our test will be next thursday (02/03/11).  There is a webassign due tomorrow (tuesday the 25), and don't forget to start the second set of book problems which will be due on the day of the test.  We will also be turning in the first set of book problems that we did before finals.


The next scribe will be Ann Marie C.


Good luck!

Solutions and Electrolytes

    We began today's class by going over the answers to the Classifying Chemical Reactions post lab.  In case you missed it:


Reaction 1:  2Mg + O2 ---> 2MgO
                  Synthesis
Reaction 2:  2HCl + Mg ---> MgCl2 + H2
                  Single Replacement
Reaction 3:  (NH4)2CO3 ---> CO2 + 2NH3 + H20
                   Decomposition
Reaction 4:  CaCO3 + 2HCl ---> CaCl2 + H2O + CO2
                  Double Replacement
Reaction 5:  CuCl2 + Zn ---> ZnCl2 + Cu
                  Single Replacement
Reaction 6:  3CuCl2 + 2Na3PO4 ---> Cu3(PO4)2 + 6NaCl
                  Double Replacement
Reaction 7:  NaOH + HCl ---> H2O + NaCl
                  Double Replacement


    Next, Mr. Lieberman went over some new notes.  We talked about solutions and electrolytes.  A Solute is what is being dissolved in a substance (in this case we mainly focused on water).  A Solvent is what is doing the dissolving.  For example:  You have water and salt.  Water is the solvent and salt is the solute because it is being dissolved in the water.  A solvent can be anything from a liquid, solid, or gas.  Water dissociates ionic compounds into its ions (meaning that it takes them apart).  Example:  NaCl ---> Na+ + Cl-.  Another example we used is the rock salt you pour on your driveway and sidewalks in the winter.  The formula for it is CaCl2 but when it dissolves in the snow (water) you get Ca (charge of 2+) and 2Cl (charge is -).  


    If the compound happens to be covalent, the formula stays the same but changes whether it is a gas, solid, or liquid.  For example:  CO2 (g) ---> CO2 (aq).  

    Electrolytes are basically ionic compounds that carry a charge.  Strong electrolytes are a solution containing enough ions to carry a current efficiently (complete ionization).  A weak electrolyte is a compound that doesn't completely dissociate (small amount of ionization).  


    Electrolytes are essential to our lives.  Without them we would die.  Athletes drink gatorade because they want those electrolytes.  Mr. Lieberman also brought up your nervous system.  Neurotransmitters work as ions too.  Your nervous system passes electrical currents all the time.  


    Mr. Lieberman conducted an experiment to show the presence of electrolytes.  The goal was to light a lightbulb.  At first this was attempted by placing a beaker of salt under the lightbulb where the metal ends were.  The lightbulb did not light.  Then the same thing was done with sugar.  The bulb still did not light.  Water was used next but the electrolytes were to weak to light the bulb.  When adding a little salt to the water the electrolytes were strengthened and were able to light the bulb.  When even more salt was  added the electrolytes were even stronger and the light was brighter.  

Strong Electrolytes

No Electrolyte

Weak Electrolytes

    That sums up today's class.  We received a worksheet titled Dissolving that you should begin to complete.  The unit test has been postponed to next friday.  Hope everyone has a happy Thursday and a good night!!  

The next scribe will be..................... Nicole C.

Good Luck! :)

Precision, Accuracy and Measurements

Today we began by turning in our "What Chemical Reaction Labs."  We received our quizzes back and went over the problems.  Then Takashi, Chris, and Rachel played a game of darts.  The whole point of the game was to understand precision and accuracy.


Precision measures the reproducibility of your value.  In other terms precision means: how often can you get the intended outcome.  For example, in labs we want our results to be reproducible (the results should be the same each time).


Accuracy is the extent to which a measurement approaches the true value.  It is how close you are to the theoretical target (in this case the bulls eye).


We went over and took notes on precision, accuracy, and measurements.  In class we will be using the SI system which is based on the metric system.  Mass in grams (g), length in meters (m), and volume in liters (L) are the base units.  You will need to know how to convert different units.  The metric system is based on factors of 10 so it shouldn't be too complicated but if you need help here is a chart that may be useful. 

Factor	Prefix	Abbreviation
10 6	mega	M
103	kilo	k
10-1	deci	d
10-2	centi	c
10-3	milli	m
10-6	micro	µ
10-9	nano	n
10-12	pico	p

In the next class we will finish up our notes and cover temperature, significant figures, and scientific notation.  The homework is:
-Webassign 1.3 (due tomorrow if not already finished)
-Metrics worksheet 
-Study for quiz on Wednesday (Measurements, conversions)


The next scribe will be Chris A.  


Good luck!