8-27-09

Thursday August 27, 2009
Today in class, we simply just took notes and discussed what we were taking the notes on. Here are the notes from today’s class:

Mathematical Operations Using Scientific Notation
3. Division
The M factors are divided, and the exponent of the denominators is subtracted from that of the numerator.
Ex.
D=M/V = 5.44/8.1 X 10^7-3 g/mol
=0.6716049383 X10^3
=6.7 X10 ^2 g/mol

Using Sample Problems
Analyze
The first step in solving a quantitative word problem is to read the problem carefully at least twice and to analyze the information in it.
Plan
The second step is to develop a plan for solving the problem.
Compute
The third step involves substituting the data and necessary conversion factors into the plan you have developed.
Evaluate
Examine your answer to whether it is reasonable.
1. Check to see that the units are correct.
2. Make an estimate of your expected answer.
3. Check the order of magnitude in your answer.
4. ***Be sure that the answer given for any problem is expressed using the correct number of significant figures.***
Ex.
Calculate the volume of a sample of aluminum that has a mass of 3.057 kg. The density of aluminum is 2.70 g/cm^3.
V= M/D 3.057 kg converts to 3057 grams using conversion factors

V= 3057 g / 2.70 g/cm^3
V= =1132.222……
V=1130cm^3= 1.13 X 10^3 cm^3

Direct Proportions
Two quantities are directly proportional to each other if dividing one by the other gives a constant value.
-read “y is proportional to x”
Inverse Proportions
Two quantities are inversely proportional to each other if their product is constant.
-read “y is proportional to 1 divided by x”