Solution Formation Lab

Today was late arrival and we had shortened periods, which means we spent the whole period working with our lab groups on the solution formation lab. The goal of the lab was to determine the effect of crystal size, temperature, and degree of mixing on the solution formation. Each group had to develop their own procedures to test the three variables for a solution of copper sulfate disolved in water.


For our groups procedures, we kept all of the variables the same except for the one we were testing, in order to make sure the that change in results is because of the change on the variable that we controlled. For example, the first part of the lab was to determine how the size of the crystal effected the solution formation. By testing three different sized crystals of copper sulfate at the same temperature, our group got the conclusion that the larger the crystal, the longer it takes for it to dissolve.

The second part of the lab was to test the effect of the temperature of the solvent on the formation. Our group used water at three different temperatures and the same amount of copper sulfate, and by dissolving copper sulfate in all of them, we discovered that if the temperature is higher, the crystals will dissolve faster.

The last part of the lab was to test the effect of the degree of mixing on the formation the of the solution. To test this, our group mixed the solution with a stirring rod at different speeds but the same amount of copper sulfate and at the same water temperature. By keeping time, our group found that the faster you stir, the faster the crystals will dissolve.

So, that is pretty much it for our shortened class.

The conclusion part of the lab is for homework and it is due on Thursday.
The next scribe will be Michelle T.

Enthalpy Thursday

Today was a pretty easy day. We started off class by going over some new notes.

We learned that because most chemistry reactions take place at constant pressure, we can say the a change in enthalpy is equal to the heat supplied. The symbol for enthalpy is "H" so we can write: (the change in)H=q. This is good to know becasue it is not possible to measure the the change of H in a lab but we can measure q which is the same as H. Yay!

We also leanred about how exothermic and endothermic reactions relate to enthalpy. For an exothermic reaction, the heat released corresponds to a decrease in enthalpy, sooo...(the change in)H<0.>

For an endothermic process, an input of heat corresponds to an increase in enthalpy, which means (the change in)H>0. An example of this is photosynthesis.

We also learned that all chemical reactions either release or absorb heat. For exothermic reactions, the heat is written on the right side of the arrow, like it is a product: reactants --> products + energy as heat (H).

For endothermic reactions, the heat is written like a reactant and written on the left side of the arrow: reactants + energy as heat (H) --> products.

Mr. Lieberman also taught us how to use stoich in an equation to find the change in H.

We solved the sample in our notes.

When 1 mole of methane (CH4) is burned,

890 kJ of energy is released. Calculate the

(change in)H for a process that uses 5.8

grams of methane.

First, we need to make sure that it s a therodynamic reaction. The problem tells us that energy is released which means it is an exothermic reaction.

Then we write the chemical equation with the energy written as a product in this case:

CH4 + O2 --> CO2 + 2H20 +890kJ

Finally, we use stoich to solve the equation:

5.8 grams CH4 x 1mole CH4/12 grams x 890kJ/1 mole= 322.63kJ

The last ratio is the ratio of the amout of kJ used per mole which they give us in the

problem. You can write the amount of energy as a negative because it is an

exothermic reaction, but you don't need the negative because the problem already

says that the energy is "released."

So that is pretty much the notes we went over in class today. Mr. Lieberman gave us the rest of the class period to work on the labs from Tuesday and Wednesday which were due at the end of the period. For homework we had a WebAssign, a pre-lab, and a worksheet.

The next scribe will be Mollie M.

Colorful Concentrations

Today in class we started off by turning in our Density of Pennies Lab. We then went over the concept of percent error and how to calculate it. The formula to find the percent error is theoretical value subtracted from the actual value, then divide that by the theorectical value and then that answer is multipled by one hundred. Mr. Lieberman said this is important to know and that we will be using it continually throughout the year.



After that, Mr. Lieberman showed us a demonstration using salt water, two different types of beads, and isopropyl alcohol in a plastic bottle. When Mr. Lieberman shook the bottle, the two liquids combined and the beads were everywhere, but then the white beads floated to the top and the blue beads sunk to the bottom. As the water and alcohol began to seperate, the white beads slowly moved down and the blue beads floated up and the two met in the middle. The point of the demonstration was to show how density effected where the four substances stayed in the bottle and what happened when they were mixed together.



For the last half hour of class we started the Beverage Density Lab. Mr Lieberman showed us how to use the pipet -not with your mouth :). Then we began the lab by placing the beaker on the balance and "rezeroing" the balance. Next, everyone poured each of the different concentrations- 0%, 5%, 10%, 15%, and 20%- into idividual beakers and took them back to the lab tables. Yes, the mixtures were very pretty colors but not to be mistaken for Gatorade : ) We then used the pipet to measure out 5 mL, not 10 mL, of each concentration and put it in the big beaker to measure the mass. Our group's data showed that the mass of the concentrations increased as the amount of sugar in each mixture increased. We then used the mass we measured and the volume of 5 mL to calculate the density. Tomorrow we will continue the lab and do part B. The finished lab will be due Wednesday and Mr. Lieberman explained that we will need to do another graph for question number one of the post-lab questions.

The next scribe is Mollie M.