Thursday November 29th

Greetings Chemistry students!

You should have your Unit 8 Notepacket and a handout from Mrs. Windsor... otherwise how did you get to this webpage?

General rules for the computer lab - do your chemistry work. This is not time to work on stuff for other classes, check your email, or anything else. So don't. Do chemistry.

First, you are going to download a powerpoint on acids and bases and take notes. Download it HERE! You can save it if you want, otherwise just choose open.(For GovSchool students on Friday's field trip, you also need these notes and to get a lab from Mrs. Windsor. You need to do as much as possible on that sheet.)

Once you are done with the notes, you are going to read through the interactive instructions on the handout from Mrs. Windsor. Then click HERE to go to the interactive and do it! (Alkali = base!)

Once you are done with the interactive, you are going to go take the Radiation Quiz and answer the questions. We live at 500 feet. (This is the one I breezed through recently.) We will be talking about the nuclear particles and reactions on Monday.

Then get your homework (it's pink!) from Mrs. Windsor and get started. She will be checking it and going over it tomorrow.

• There will be an acid base quiz on Monday.
• Tuesday = Benchmark 3
• Friday = Chemistry Assessment (you took at beginning of year)
• Wednesday the 12th = Chemistry SOL

Density

Monday was a get-to-know-you sort of day. Students started with an informal survey and drew a picture of themselves that I will use to help learn their names (I am terrible at names). I familiarized the students with classroom procedures, discussed homework and classwork, and let them know how class was going to run.

 

We have made sure that everyone had a good handle on density in regards to definition, math and formulas, and what it actually means. Density is how close together the particles are in a substance. If they are close together the substance is more dense. If the particles are far apart, the substance is less dense. I do not float in Lake Anna, but I do float in the ocean - therefore I am more dense than Lake Anna and less dense than the ocean.

Things that are more dense-sink, things that are less dense-rise to the top, things with similar densities-mix. If you were to pour liquids in a random order layers form because of the differences in density. Here is a photo of a demo.

Today students reviewed endo and exothermic reactions.

Endothermic reactions absorb heat and get warmer (End Up).

Exothermic reactions lose or release heat and get colder (Exit down). 

To test this out, look at a whack-a-pack and make observations. The pack starts off at room temperature and when you hit it, the reaction occurs. This is a chemical reaction for a few reasons - one you can hear it fizzing. Two it blows up so a gas is being formed (1 of the 4 ways you know a chemical reaction has occurred). And Three there is a temperature change (another of the four ways). The pack gets really cold which means it is releasing heat and this is an exothermic reaction.

Watch this little video to see how it works. These are available at Dollar Tree at Valentine's Day if you are interested.

Solutions, Suspensions, and Colloids... oh my!

Solutions are homogeneous well-mixed mixtures that cannot be separated easily (a change in phase) - like kool-aid or saltwater. Suspensions will settle and separate over time because of gravity or because of differences in density - like oil and water or orange juice with pulp. Suspensions are heterogeneous. Colloids are weird. Colloids should settle and separate over time but because the particles are super-tiny just running into each other (Brownian motion) keeps them in suspension. Colloids can also represent two different phases so if it seems weird like you cannot classify it as just one phase - like fog, jello, whipped cream - it's a colloid.

We also discussed colligative properties. Adding solutes to a solution changes basic properties like melting points and boiling points, no matter what solute is added. A perfect tie-in for today. Salt is put on our roadways to LOWER the freezing point of water to about -4*C. Because the freezing point is lowered, the ice appears to melt and stay liquid, thus making our roads less icy. They do not salt the roads in places where the normal daily temperature is below 0 because the salt would have little effect.

Because it doesn't matter what the solute is, sugar could be used for the same purpose - it is just a lot more expensive! To read more, click here. 

 

Electrolytes can conduct electricity because the solute breaks up into ions and the ions can carry the electric current. Pure water does not conduct electricity - but water with solutes in it can. We did an in-class demo similar to this one to test some solutions. Salt water does conduct electricity, but sugar water does not because of the carbon. Gatorade conducts electricity but barely because of the high sugar amount in the drink.

Molarity is moles/Liters and is a quantitative way to measure concentration. Molarity descirbes with numbers if a solution is dilute or concentrated. It is a pretty easy formula so students zoomed through it. Molarity changes with the amount of solute OR the amount of solvent (liquid) so we will be discussing dilutions tomorrow.

Phases of Matter... and OOBLECK

Today students went over the differences between solids, liquids, and gases. This is material they should be familiar with, but we are reviewing it and going a little more in depth. We discussed what the particles look like, the densities, and how much energy they have. We also discussed phase changes and worked on two phase change graphs the students will see on the SOL, how to label them, and how to answer questions about them.

We also discussed matter (everything in the universe is made of matter) and how you can classify it as substances or mixtures. Substances can either be elements from the periodic table or compounds made up of more than one element. 

We finished class by doing a lab with oobleck. Oobleck is technically a non-Newtonian Fluid which is really hard to define in layman's terms. Scientifically it is also a colloid because the cornstarch particles are very tiny and evenly dispersed throughout the water, but will not settle out. Anyway.

The students mixed up their oobleck and then performed a series of tests to determine whether the oobleck was more like a liquid or more like a solid (they had to make a choice). Fun was had, messes were made, people were learning. Life was good. Here is a photo of Caroline (look at her mess!).

To watch a mythbusters about oobleck and how you can walk on it(!) - click here.

Homework for tonight are Boxes G and J on the green homework sheet

Phases and Phase Changes

We discussed solids, liquids, and gases. We talked about the amount of energy the particles had and how the particles move. We discussed whether they had definite or indefinite volumes and shapes. We talked about why exactly we can't walk through walls, but why we can walk through gases and liquids.

Next we discussed the phase changes that happen between solids, liquids, and gases. These changes can be represented on one of two graphs. We talked about the graphs, labeled them, and and answered questions about them. We finished the day with a game of SWAT where the class was divided into two and one person from each team went head to head to be the first to swat the correct part of the diagram.

Solutions

Today in class we discussed solutions. Solutions are homo- geneous mixtures comprised of solutes dispersed in a solvent. Water is the universal solvent, but not the only solvent. For example, a marshmallow is a solid (sugar) solute dispersed in a gaseous solvent (air).

Solubility is how well something dissolves. Some things are very soluble, and some are insoluble (do not dissolve).

Solutions are said to be saturated if they are holding all the solute that they can. When the solute starts to build up on the bottom, you know a solution is definitely saturated (like the dark blue solution on the right). Solutions are unsaturated if they can dissolve more solute (like the two light blue solutions on the left).

Solutions can be super-saturated if they are heated because they can hold more solute than normal. Even if you cool these solutions back down, they will still hold this additional solute in solution. Sweet Tea and all candies are made by first making super-saturated solutions and then cooling them.

For an excellent website about all of these topics and others regarding solutions that have and will be covered in this unit - check out this useful website.

Marshmallow Madness

Here are D'artagnan and Harriet the marshmallows, happily in love (and unaware of their impending doom).

After 1 minute in the microwave, they look quite a bit different. So what happens?

Marshmallows are colloids (permanently suspended homogeneous mixtures) of sugar and air. When the marshmallow is heated, the air particles get excited and move faster and more, so the air expands and so does the marshmallow.

When the microwave cuts off, the air cools down dramatically, the gas particles contract, and the marshmallow shrinks.

Now you know... and knowing is half the battle.

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 and did well.

Combined Gas Law

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

PV = PV
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.

Gases

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.