Friday, April 29, 2011

acids and bases

Today we started discussing acids and bases.

Acids have H+ and donate them, they have the smaller numbers 0-6.9, they turn litmus red, and have sour tastes. 

Bases have OH- and want H+ to make water, they have Bigger numbers, they have a pH between 7.1 and 14, they turn litmus Blue, and they taste Bitter. 

If you mix an acid and a base together, then there is a neutralization reaction. A neutralization reaction is also a double replacement reaction. In neutralization, the acid and base combine to form a water and a salt. The water and the salt are neutral (hence the name).

pH measures the concentration or molarity of H (Hydrogen ions) in a solution. That's why the H is capitalized.

pH + pOH = 14. So if you have the pH, it is easy to get the pOH... just subtract from 14. There are some fun interactives for acids and bases linked at the bottom of this webpage. Check out the Alien Juice Bar.

Tuesday, April 26, 2011

Combined Gas Law

The combined gas law combines the work of Charles, Boyle, and Gay-Lussac.

nT nT

Basically, memorize one formula and then use only the variables you need, so sometimes you need PV = PV, and sometimes V/T = V/T.

This will help you with placement and deciding whether you should multiply or divide.

Sunday, April 24, 2011

Ideal Gas Law

Ideal gases do not actually exist, but we pretend they do and use the Ideal Gas Formula of PV=nRT.

One of these variables will not be given to you and you have to solve for it. This does not seem difficult after stoich, so students dove in, did well, and finished early.

Saturday, April 23, 2011

Beginning Gases

Today we started learning about the behavior of gases and the factors that affect them. Gases are lightweight fast moving particles that generally have a lot of empty space between them. Because of this, they are easily compressible (pictured left). If not contained, gases can spread (or diffuse) to fill any size and shape container.

Gases are affected by pressure, volume, number of moles, and temperature. Changing any one of these variables, changes all the others.

Today we also learned the formula for the Law of Partial Pressure. Basically partial pressures add up to form total pressure. If the total pressure is given then you subtract the partial pressures.

We are still working on moles and making sure we have stoichiometry down pat.

Thursday, April 21, 2011

Gum Lab

Students each had a piece of gum and observed the gum by weighing it, drawing it, and smelling it. All the gum was Dubble Bubble, but the Cry Babies were the most popular.

Next the students chewed the gum for ten minutes. While they were waiting we watched How Its Made on bubblegum (the video is linked on the side if you want to check it out). We also had a little fun blowing bubbles.

After ten minutes, students did more observations and re-weighed the gum. The gum weighed less... why? Because the sugar dissolved and was lost. Using this weight difference, students determined the percent composition of sugar in the gum they chewed. They also can convert the grams to moles and determine how many moles of sugar were in the gum.

Monday, April 18, 2011


Today students took a mole challenge to see how much they knew about moles... besides their favorite number. The high score was a 9.5/10 so I must have stumped them. They did do better than they thought they would... and most of them were a bit mad when they saw what the answers were to the ones they didn't know.

For moles there are basically three conversions to know.
1 mole
6.02 x 10^23

1 mole(molar mass) grams (add weights from PT)

1 mole
22.4 Liters

Today we learned about Avogadro's theory about gases and then practiced converting using our new favorite number, 22.4. Avogadro, that handsome devil, did a lot of important stuff with moles and is also the guy who gave us our other favorite number 6.02.

Sunday, April 17, 2011

What is a mole?

Today, we started talking about moles. Moles are used to count atoms. There are 22,000,000,000,000,000,000 quintillion atoms in a grain of sand and even counting grains of sand is a pain. Because atoms are so tiny, we use the mole to estimate.

There are 6.02 x 10 ^23 molecules in one mole. That's a whole lot. This is our new favorite number because it needs to be memorized. We practiced converting from moles to molecules.

Next we discussed molar mass. Molar mass = 1 mole and it also equals atomic mass from the periodic table. To find the molar mass of carbon dioxide you find the mass of carbon and two oxygens and add them together. Finding molar mass is not difficult unless the molecule has tricky subscripts (which we have been practicing).