Some chemistry calculations require the use of a formula and cannot simply be done by unit conversions. This then requires the use of algebra, so we are going to do a quick refresher. We'll use actual chemistry formulas though just for fun!
Operation signs will be in red so as not to confuse them with other notation.
Starting with a simple one, density is calculated by mass divided by volume. D = M/V
Example: We have a 12 g sample of metal that has a density of 7.5 g/ml. What is the volume?
Substituting the information into the formula, we get 7.5 g/ml = 12 g / V
To solve for volume, we need to multiply both sides by V:
V * (7.5 g/ml) = 12 g
Then divide both sides by 7.5 g/ml
V = 12 g / 7.5 g/ml = 1.6 ml
The grams cancelled each other out and the ml were in the denominator of the denominator, so they came up to the numerator.
Now let's try the formula for the potential of a battery E = Eo - (.0592/n)*logQ
Example: The standard potential, Eo, is 1.72 volts. The measured potential, E, is 1.34 volts. If the number of electrons exchanged, n, is 2, what is the reaction quotient, Q?
Substituting the information, we get 1.72 = 1.34 - (.0592/2) * logQ
To get Q alone, you have to work from the outside in toward Q, undoing things in the reverse order of the order of operations. So you do addition and subtraction first, then multiplication, then higher order things like squaring and logs.
Subtracting 1.34 from both sides and simplifying, we get .38 = - .0296 * logQ
Now divide both sides by -.0296 and get -13 = logQ
Taking the inverse log (2nd log) of both sides, we get Q = 1 x 10^-13
Okay, we're ready for a quiz. The answers are on the answer page.
This is a topic that is easy to learn in person, but difficult in a worksheet like this. If you are having trouble with this, please tell me in the fall and I would be happy to sit down and refresh algebra with you. It would only take 10 minutes to get you as fast as everyone else. But if you don't do a refresher, you will struggle all year! Or you can get hold of me now at 651-486-9697 or jcaskey@ties.k12.mn.us
Also, you can visit the math refresher part of Mr. Logan's page. Choose algebra from the options given.
Return to the introduction page and continue with your tutorials.
