Tuesday 9.7.10

Today in class, we started off by going over the basics of density (the formula and units of density). The formula for density is . In order to find mass and volume we need to know the units of mass (grams (g), kilograms (kg), and milligrams (mg)) and volume (milliliters (mL), Liters (L) and cm (cubed)). We followed this up with examples of finding density to get a better understanding for the material (Ex: If the mass of a powdered substance is 6.52 kg and the volume is 22.4 L, what is the density? You would then go on to put the mass (6.52kg) over (divide by) volume (22.4 L) and get 6.52kg/22.4L= .291 kg/L, and because it is multiplication, the answer has to match the lowest amount of significant figures, in this case, 3).

We also did an example of the different densities of substances in water and found out the a substance with higher density than all the rest sinks down to the bottom and the substance with less density than all the rest, floats to the top. All the substances in between then order themselves from top to bottom going from least dense to most dense in a totem pole looking fashion. We finished up class with a Density lab. For this lab we needed a regular object, an irregular object, a ruler, a balance and a 10 mL and 100 mL graduated cylinder.

In this lab we found the mass of a regular solid object (a metal rectangular prism) using the balance to "mass" it and the volume using the formula of Length x Width x Height. We then used these measurements to calculate the density of the solid using the equation .

To then find the density of an irregular solid object (a metal nail) we measured the mass using a balance. To get the volume we filled a 100mL graduated cylinder about half full of water. Once we measured the exact volume of the water, we added the nail and then measured the volume again. To get the volume of the nail, we subtract the initial volume of the water from the volume of the water with the nail. Once we have the mass and volume we again use the formula to calculate the density.

Finally, we measured the density of a liquid. We first measured the mass of an empty 100 mL graduated cylinder. Once we got that measurement, we filled the cylinder about one third full. We then measure the mass of the cylinder plus the liquid and then subtract the cylinder's measurement to get the mass of the liquid. We then get the volume of the liquid simply by measuring it in the graduated cylinder. Once we have the mass and volume, we calculate the density one final time by using the formula .

Our homework for tonight, is to complete pg. 9 which Mr. Paek gave out at the beginning of class to go in our notebooks. This is simply just more examples of finding the different components of the density formula ().