Thursday, March 27, 2008

Example Conclusion from Introduction to Solutions Lab

The purpose of this lab was to determine if a sugar cube or small grains of sugar would dissolve faster. Before doing this experiment, we predicted that the small grains would dissolve faster. We made this prediction because the sugar grains are not together and the water molecules would have easier access to them. During our experiment we saw that when the two types of sugars were stirred in the water, that the grains dissolved much more quickly than the sugar cube. This occurred in all three of our trials. On average, the grains dissolved in 1.24 minutes and the cube took 1.58 minutes to dissolve.
The sugar cube probably dissolved less quickly because it was more tightly packed and the water molecules couldn’t get to all of the sugar molecules all at once. The grains dissolved faster because they had more surface area, which allowed more water molecules to surround the sugar and dissolve it. Some possible sources of error in this experiment were issues with starting and stopping the stopwatch, losing sugar when putting into the beaker, and changing the stirring rate while dissolving. These errors may have affected either the time it took to dissolve the sugar samples or the time that we recorded. If I tried to do this experiment again, I might try to standardize the amount of sugar we add more precisely, and perhaps create a machine that would stir the solutions at an equal rate.

Thursday, March 6, 2008

Answers and Equations for "Stoichiometry and Percent Yield Practice"

2. Correct Formula: 2K + 2H2O --> 2KOH + H2
Answer: a. 1.25 mol H2
b. 83%

3. Correct Formula: 3CO + Fe2O3 --> 2Fe + 3CO2
Answer: a. 365.2 g Fe
b. 82%

4. Correct Formula: Ca + Cl2 --> CaCl2
Answer: 3.20 mol Cl2

5. Correct Formula: 2KI + Br2 --> 2KBr + I2
Answer: 41.2 g Br2