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.

Mole Day 2012

Today is Mole Day! Mole day celebrates Avogadro's number of 6.02 x 10 to the 23rd power a ginormous number that helps us keep track of itty bitty atoms.

Students learned about moles way back in Unit 1 and already know the basics. We have been honing those skills all along - especially since starting Unit 5 Stoichiometry. 

For moles there are basically four  conversions to know.

1 mole
6.02 x 10^23

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

1 mole
22.4 Liters

Mole

Mole

The mole/mole conversion is used to convert from one chemical to another using the coefficients from a balanced equation. 

Students came up with team names related to moles and designed team flags. Then teams started in on the Avogadro Cup with silly activities related to moles (both animal moles and scientific moles) like "Pin the Nose on the Mole" and "Mole Celebrities" and the "Periodic Table Puns." Students also did CheMOLEstry activities like mole conversions and practice SOL questions. 

Theoretical and Percent Yield

Theoretical yield is how much product you can make with given reactants. To determine theoretical yield, do a normal stoichiometry calculation. 



Actual yield is how much is actually produced when the reaction is performed. 

Percent yield is how well you do. Percent yield calculates how close to the theoretical yield you are. A high percent yield means that your actual yield was close to the theoretical yield, the reaction worked the way it was supposed to it, and it was efficient and accurate. 

Why doesn't theoretical yield equal actual yield very often? ERROR!

Error can include impure substances, uncalibrated equipment, improper procedure... all kinds of things.

Percent error measures the amount of error. Small percent error means things went well and the actual yield was close to the theoretical yield. 

Percent yield plus percent error should equal 100. 

Limiting Reactants

If you mix two chemicals together as reactants it is unlikely that both reactants will be used up completely when forming products. One will be used to completion, this one is the limiting reactant, and will limit how much product can be made. The other will be used up until the other reactant runs out and there will be some left over, so it is an excess reagent. 


If you have 8 cars and 48 tires, which one is limiting? Which one will you run out of first?

In this example it is easy to "see" which is the limiting and which is excess. When looking at quantities of chemicals it is not as easy to "see."

To determine which chemical is limiting, convert from the given reactants to a product (it does not matter which). Whichever reactant produces the least amount of product is limiting. 

4 NH3(g) + 5 O2(g)4 NO(g) + 6 H2O(g)

If you have 2.00 grams of ammonia and 4.00 grams of oxygen gas which is limiting?

Because the oxygen produced less of the product nitrogen monoxide, oxygen is limiting. 

Stoichiometry

Stoichiometry is the most important part of chemistry and why chemistry is so useful in real life. With a balanced equation, stoichiometric conversions can be used to calculate how much product will be made, or how much reactant is needed to produce a certain amount of product.

Stoichiometry uses the three mole conversions that students are familiar with from unit one, plus the mole/mole conversion. A mole/mole conversion uses the coefficients from a balanced equation to convert from one chemical to another. You can only compare elements or chemicals when they are both in mole form. 

Using this equation N2 + 3 H2 --> 2 NH3 the following calculations can be made using stoichiometry. 

Entropy - Disorder

Entropy is a chemistry word for disorder. An increase in entropy is spontaneous. By looking for four things in a reaction, students can determine whether a reaction is spontaneous or nonspontaneous by looking for an increase in entropy. 

Exothermic reactions are spontaneous and show an increase in entropy. 

Gases are messier than solids, so a reaction that forms a gas shows an increase in entropy. 

More molecules show an increase in entropy. Count the coefficients on either side of a balanced equation. If the products have more molecules then there is an increase in entropy and the reaction could be spontaneous. 

A decrease in the size of molecules (count atoms making up the molecule) is an increase in entropy. 

Students look for all four things and decide whether the overall reaction would lead to an increase in entropy and be spontaneous. 

Le Chatlier

Students learned about reaction rates and how to increase them. They also learned about reversible reactions and how Le Chatlier's principle influences shifts of equilibrium in reversible reactions.

Basically as you apply a stress to a system, the system will shift in response to the stress. If you add one of the molecules it will shift away from that molecule. If you take away a molecule, it will shift towards it to make more. Heat works the same way.

Pressure is the tricky one. If pressure is applied to an equilibrium, then the reaction will shift to the side that has the least amount of molecules (count the coefficients).

Reaction Rate Basics

Reaction Rates are affected by a few things. Without telling them the point, the students had a quick demo where they had to dissolve sugar cubes the fastest. 

The things that speed up reactions are:

• Temperature - warmer is faster
• Surface Area - small pieces have more surface area
• Concentration - the more water, the faster sugar will dissolve
• Catalyst - lowers the activation energy and speeds up the reaction
• Agitation - shaking or stirring increases the frequency of collisions.

Balancing Reactions

Students are learning to balance equations. Today they learned that reactants are what you start with and are on the left side of the equation. Products are on the right side of the arrow and are what is made by process of a chemical change.

Because of the Law of Conservation of Mass, the number of atoms have to be equal on both sides. To balance an equation, the coefficients are changed. Coefficients are the big numbers in front that tell you how many molecules there are. The subscripts (the little lower numbers) are not allowed to be changed because those are there to make neutrally bonded molecules (what we learned in the last unit.

By changing the coefficients and counting the number of atoms on both sides of the arrow, balancing can be achieved.

Polar and NonPolar Covalent

Anyone who has ever had to share something with someone else knows that sometimes isn't exactly even. Covalent molecules or bonds are no different. 

If a molecules is nonpolar covalent, it is sharing its electrons equally. The best example of this is in diatomic molecules. Diatomic molecules are two of the same atom bonded together - so they would have exactly the same pull. Symmetrical molecules are also nonpolar.

 

Polar covalent bonds occur when electrons are not equally shared. One atom, usually more electronegative, has a stronger pull on the electrons and shares them unequally. The other atom that is less electronegative has a smaller hold on the electrons and is thus can be slightly positive. 

One way to remember this is... "Polar Bears do not share... equally."

VSEPR

Valence Shell Electron Repulsion Theory

Electrons do not like each other and when looking at molecular structures - electrons and unshared electrons (the two dots paired together) will space out evenly so they are as far apart as possible.

Most of the names of the shapes of hints like tri, tetra, planar, etc. Students need to memorize these shapes and be able to visualize them for given formulas.

For help with VSEPR - read this.

Covalent Bonding

If it is a - and -, the bond is covalent. The electrons are shared in the bond. To get the formula, you have to draw the Lewis Dot structures for the elements and connect the dots that don't have friends. You write the formula based on your drawing. To name it, use prefixes to indicate the number of atoms in the formula and the second one ends in -ide. For these it doesn't matter which element comes first.

Ionic Bonding

Students learned about ionic bonding. Ionic bonding happens between metals & nonmetals (positives & negatives). The electrons are given and taken in this ionic bond. To get the formula, you criss cross the charges. To name it, you say the name of the metal, then the name of the nonmetal with an -ide ending. If it is a metal from DForP block, then you use a roman numeral to indicate the charge of the metal.

After learning the basics, students in first period practiced with an activity called "speed dating." Students were metals ("boys") and nonmetals ("girls") and practiced dating, bonding, and naming the ionic bonds they would make with their partners. The funny thing is that being a male did not necessarily make your character a "boy." :) Students really got the hang of bonding, were able to work with and help a variety of partners, and had fun. We will continue this activity tomorrow in all class periods.

Now that we understand ionic bonding, students should find this cartoon amusing.

Ionic Bonds for Dummies

Here is a cool interactive where you can build models to simulate ionic bonding.

Metals = Roman Numerals

Time to learn about roman numerals.... Here is a handy clock if you are unfamiliar with them. Pretty much you need to know 1-7. 1 is represented with I, five with V and 10 with X.  4 and 6 and 7 is where it gets tricky. 4 is 1 before 5 - so its Roman numeral is IV. 6 is one after five so its roman numeral is VI.

Students also learned how to identify the charges of metals with more than one oxidation state using Roman numerals. Metals in the D, F, and lower P get Roman numerals - basically all metals but the S block, Aluminum and Boron get roman numerals. The roman numeral tells you the charge. We have to use this system because those odd metals can actually be found in more than one form - some with 2 possible charges - some with more than four!

Valence Electrons and the charge of ions

Students learned about valence electrons. Valence electrons are the outermost electrons and are the electrons that are used for bonding and participate in reactions. Valence electrons are only found in the S and P blocks. The max number of valence electrons is 8. Students practiced counting valence electrons and drawing Lewis Dot Structures.

Students also practiced identifying which noble gas an element wanted to be like. All elements want to be like two noble gases - it is just a matter of figuring out which is closer. Elements want to be like noble gases because they have full outer electron shells, or full valences. This makes them stable and non reactive which is why noble gases are sometimes called the inert gases.

Today students learned how to use valence electrons and dot structures to determine the charge of an atom. Atoms either want to gain electrons or lose electrons to become like those noble gases they envy.

• Ions are atoms or molecules that have a net charge, either positive or negative. There are two kinds of ions:
• Anions are negatively charged ions because they have negative net charges. This means that there is a greater number of electrons (-) than protons (+). For example, the anion, fluoride (F ^1-), has a one negative charge because it has a total of nine protons and ten electrons. Thus, the net charge for fluoride is 1 negative.
• Cations are positively charged ions because they have  positive net charges. This is due to these ions having more protons (positive charges) than electrons (negative charges). For example, calcium (Ca 2+) is a cation ion with 20 protons and 18 electrons. The net charge for Calcium is 2 positive. (from here)

Formula Writing

Today we discussed how to write chemical formulas, and what the numbers associated with a chemical formula mean.

Coefficients are the big numbers in front and are distributed to the whole molecule (which means you may have to multiply). Coefficients tell you how many molecules are present. 
     3He = He He He :)


Subscripts are the little lower numbers and they indicate the number of atoms and only apply to the atom it is to the right of. Subscripts tell you how many of each atom are present. Students wrote their name as a chemical compound and thought it looked pretty interesting. Some students have long formulas, other short.

We then led into counting atoms for real chemical formulas using subscripts and coefficients.

Be careful....

Here is the wonderful website these images came from. You may find it helpful.