Colligative Properties Lab

Today in chemistry we did a lab that tested the colligative properties. In the lab we boiled a solution of water and an unknown substance to its boiling point. We used four beakers that were each filled with about 50 ml of water. The first beaker was the control group so we didn't add any of the substance. In the second beaker we added about 5 grams of the substance and for the third and fourth beakers, we added about 10 and 15 grams respectively. While the solutions boiled we placed a thermometer inside the beaker to find its boiling point. As expected, the solution's boiling point got higher with a higher concentration of the substance. For the first calculation, you will want to use this equation:

T(b)=i x m x k(b)

You are supposed to solve for molality here. The ionic solid has 2 ions so i would equal 2. m would equal the molality and k(b) is a constant, which would be 0.51 for water. The T(b) is the Delta H that comes from the data in the lab. The homework is to finish up the post lab which is due on friday. Also there are 3 WebAssigns due on friday so keep up with them. The next scribe is Lauren C.

Colligative Properties

Today in chemistry we kicked off class with a lecture regarding colligative properties. There are 4 types of colligative properties and they are:
1.Vapor Pressure Lowering
2. Boiling Point Elevation
3. Melting Point Depression
4. Osmotic Pressure
Basically, the relations are simple. The more solute added, the more the vapor pressure decreases. The more solute added, the more the boiling point raises. The more solute added, the lower the melting point becomes. We also got a few formulas to accompany the above.

To calculate the change in boiling point(Blogger isn't letting me use equation editor, get notes off moodle to really see this):

Change in Boiling Point=molal boiling point elevation constant x molality
Traingle T subscript b= K subscript b * m

To calculate freezing point depression, you use the same formula except the constant is different. The K subscript b is repaced with K subscript f.

The van't Hoff factor basically mens that if you have a mole of NaCl, and the ions dissociate when in water, you will get one mole of Na+ ions and one mole of Cl- ions. The van't Hoff factor is i so simply modify the previous equations by multiply i to the end like so:

Triangle T subscript f= K subscript f * m * i

That pretty much sums it up for new material covered today. Liebs demonstrated these new concepts with one demo involving 4 of us as water molecules, showing that the more solute added (balloons), the more interactions we had to make with it (touching each ion), which made it harder for us water molecules to turn into our gaseous state. Also, we took some club soda, stuck it into some ice and upon opening the glass, thus releasing the CO2 which had raised the freezing point, the club soda immediately froze.

Liebs also discussed some issues with the faulty Webassign that was due today, and said he would make corrections. I know it probably frustated myself as much as did to some of you (honestly, comment if you remembered how to use sig figs before this unit started).
That's about all though. Homework tonight is to do all the worksheets you have been given this unit that are due on the day of the test, as well as the 3 remaining webassigns also due on the day of the test.

Justin J., come on down, you are the next contestant on the price is right.

Stoichiometry Returns

Today in 7th period chem we did some stoichiometry with solutions.

That was one problem that we did. Basically you can use mole ratios from a balanced equation, molar masses, and now you can use the molarities to get what you want.

Now we know the mole ratio is related in several ways:

-PV=nRT

-molar mass

-M=moles/L

We can use stoichiometry for pure substances, gases, and now solutions.

If anyone is still having trouble, I would recommend going through the notes from last semester on Stoichiometry, or watch this video:

http://www.youtube.com/watch?v=uiEc5LcsGIg

(my blogger never lets me put the actual video in... :( )

The next scribe will be...... Nicole C

Hey Guys! So today in chem class we went over notes on molarity and molality dilution.

The first concept that we talked about was the concentration of solute. That is, the amount of solute in a solution is given by its concentration. There are four units if concentration.

The first is molartiy and you can compute it by this equation, molarity (M) = moles of solute/liters of solution. This equation comes in hand when you are trying to figure out the mass of a substance needed to make a certain amount of solution at a specific molarity, or to simply find the molarity of a solution.

The second unit in with you can compute the concentration of a solution is molality, be sure to not get this and molarity confused for the sound very similar. With this unit the equation is molality (m) of solution moles of solute/kilograms of solvent.

The third unit in with you can compute the concentration of a solution is percent by mass. The equation of this unit is % by mass = (grams of solute/grams of solution) X 100.

The fourth and final way of compute the concentration of a solution is by finding the mole fraction. To find this you use the equation mole fraction (x) = moles of solute/ moles of solvent + moles of solution. For this you want to remember to have your final answer be in decimals.

The second concept we discussed was molarity and dilution. This concept talked about diluting a solution and this is simply adding more solvent, in our case water, to the solution. This will dilute the solution but remember that the amount of solute does not change and because of this, it is really easy to calculate the new molarity. All you do is take the information you have (at least three points) and plug it into the equation, MaVa=MbVb.

That was all for today’s class. Homework for Monday is to finish your lab and do the webassigns also remember to keep up with your work sheets.

The next scribe is …………………….. Rachel M.

Solubility Curve Lab

Today in 7th Period Chem we did yet another lab! This one dealt with measuring the saturation temperatures for six difference solution concentrates to construct a solubility curve.

The lab itself wasn't too complicated. Each lab group had 6 test tubes: 3 for Series 1 and 3 for Series 2. The first step was to mass the empty test tubes and record that in the lab table. Next, we added potassium nitrate to each test tube: each test tube had a specific amount of potassium nitrate it needed to be added [the lab direction sheet explains the specifics]. Once that was done, we massed the test tubes with the potassium nitrate and added that in the data table. The next step was to add 20 drops of distilled water into each test tube. Then -you guessed it- we massed the test tube plus potassium nitrate plus water....and added that into our data table. Finally, we placed the test tubes in a hot water bath, letting the potassium nitrate dissolve, then put the test tubes in an ice water bath. This cooled the solution which enabled it to crystallize. We took note of the temperature the instant crystallization occurred and recorded that into our lab table.

With all this information, there were some things that needed to be calculated in the lab. The calculations were quite simple- you just needed to use your data.

1. Calculate the mass of potassium nitrate and the mass of water in each solution

For the mass of potassium nitrate, you take the mass of test tube and KNO3 and subtract it by the mass of the empty test tube. So essentially, the second column of your data table minus the first. You have to do that for all 6 of the test tubes, so it gets pretty tedious.

For the mass of water, it's the same idea. Subtract the mass of test tube plus KNO3 and water by the mass of test tube and KNO3, which is really column 3 in your data table minus column 2.

2. Calculate the ratio of the mass of potassium nitrate to the mass of water for each solution

Here, you take the values you got from part one and set them to a ratio. For each of the 6 test tubes, divide the mass of potassium nitrate by the mass of water. That will be your ratio.

3. Multiply each ratio by 100 to get the solubility in g/100g of solvent

This one speaks for itself. Multiply what you got in in part two by 100 and you're set.

So that's the gist of the lab and the calculations. After you do that, all you have to do is place ALL of the results in a results table and plot a graph of solubility of potassium nitrate!

This lab is due Monday.

Other than that, we have a Webassign due tomorrow as well as the usual worksheets that will be due at the end of the unit.

That's all I've got for today. The next scribe will be.............................................NIRALI P! Good luck :)

Baby Monkey Going Backwards on a Pig

What a great day in 7th period chem. Arguably the best day of the year. It started out with a discussion about the english mini field trip. Summarized to be "the english teachers needed three periods to assign a project that we all knew we had." Once all of our shenanigans ended, the real chemistry began. We discussed the concept that pressure and temperature both effect solubility.

Container A is under normal pressure and therefore has a normal solubility. Container B is under high pressure and therefore has a higher solubility.

As this graph shows, when the temperature increases, so does the solubility. It is the opposite effect for gases in solution. Ce2(SO4)3 is a hipster.

We then discussed saturation. When the solubility is even with the line on the graphs, the solution is saturated. When there is less solubility than possible, the solution is under saturated. Super saturation comes when a solution is saturated at one temperature, and then is cooled down. This video shows what happens when a super saturated solution is agitated.

This is a video of a baby monkey riding backwards on a pig.

Remember to do the lab. And keep up with your webassigns.

Nicole C can do the next post. Your welcome Nicole.

Solution Formation Lab

In the shortened period today we did the Solution Formation Lab. The goal of the lab was to determine the effect of three variables on the solubility of copper sulfate in water. These variables were: crystal size, temperature, and degree of mixing. Based on my group's (Trevor B, Artie B, and myself...decide if you trust us or not) data, we came to the conclusion copper sulfate was most soluble under the following conditions:

• higher temperature
• smaller crystals
• and vigorous stirring

Conversely, the least soluble conditions are:

• lower temperature
• larger crystals
• and little to no stirring

And that's about it for today. Work on your Webassigns and the lab writeup is due Thursday. Until we meet again,

Declan G.

Joining you tomorrow will be the notorious Arthur B

Solution Chemistry Day 1

Today we started our new unit on Solution Chemistry. He handed out a new calendar and a new objective sheet. He then gave us the new notes (not online anywhere). We began the period by looking over tests that we took last week. We made another mighty fine discussion and some good laughs courtesy of the usual people. We began our notes discussion with the definitions:

Solution: a homogeneous mixture (all one colored M&M's)

Solute: is dissolved in the solvent

Saturated solution: is one where the concentration is at a maximum, no more solute is able to dissolve.

Supersaturated: a solution that is made at a higher temperature, and when it cools there is more solute than if it were only saturated.

Mr. Liebs then did a sweet demo of how H2O molecules would break dissolve a Salt (NaCl). The two substances would go through three process's before they would become a solution.

-Separation of the solute: the molecules overcome their IMF, using energy (endothermic)

-Separation of the Solvent: the molecules overcome their IMF, using energy (endo).

-Interaction of solute&solvent: attractive form between solute particles and solvent particles. "solvation"or "hydration" (water=solvent)

We had a brieft discussion about how like molecules disolve like molecules. That was the end of our discussion for todays class.

The NExt Scribe is Declan G

Intermolecular Forces

Today was all about intermolecular forces. The first type is called a dispersion force. Dispersion forces are weakest type of intermolecular force, and it is present in every molecule. Dispersion Force also depends on the molar mass of a substance.

The second type of intermolecular force is Dipole forces. Every polar molecule has dipole forces. Since polar molecules have a negative and positive ends, dipole forces cause polar molecules negative ends to attract the positive ends of other molecules and then another molecule will attach and so on.

The third type of intermolecular force is Hydrogen Bond forces. Hydrogen Bonds are basically the same concept of dipole forces, where the negatives attach to the positives, but these forces are a lot stronger. However there is a catch, hydrogen bonds can only happen when a hydrogen bonds to a N, O, or F. These three atoms have the highest electronegativities, so they will create very very polar molecules. A great example of hydrogen bonds is H2O. The intermolecular force in water is great because of the hydrogen bonds. Because the forces are so great, it can cause water to stick together, or bead. These hydrogen bonds are the reason for these to events....

Today we also did a lab exploring the effects of intermolecular forces. These effects include...

-Evaporation Rates

-Capillary Action (A Liquids tendency to climb up the walls of a narrow column)

-Vortex Formation and Relaxation (The time it takes for a liquid to relax after swirling it)

-Viscosity (Resistance to flow)

-Surface Tension (Property shown by water in above photo of the water drops on the penny)

-Beading (Shown in the above picture of the water)

The homework for today is to keep up with the webassigns. There is a reading sheet due tomorrow and all the other HW WAs are due friday. The Lab is also due on friday

The next scribe is....STUART P. Good luck bud

Non-Polar Vs Polar Molecules

The main idea today in class was non polar vs polar molecules.....

Non Polar Molecules

Non polar molecules have symmetry (the charge is evenly spread throughout the molecule) They dont have a positive and negative side. Non Polar molecule NEVER have NON BONDING PAIRS. Non bonding pairs would give the molecule a higher concentration of negative charge on one side, making it polar. It is possible for non polar molecules to have polar bonds, so be careful when determining wether or not it is non polar, its all about the symmetry.

These 2 molecules (CCl3 & BF3) are non polar because the charge is evenly distributed. SYMMETRY!

Polar Molecules

Polar molecules do not have symmetry, they have negative and positive ends. This could be causes by non bonding pairs, which will cause a molecule to have a high concentration of negative charge on one end. It could also be caused by a molecule with more than 2 different atoms around the central atom, one of them having a higher electronegativity will cause more negative charge concentration on one side making it POLAR. A great example of a polar molecule is H2O, or water. Since O has a higher electronegativity then H, all the negative charge concentrates around the O. This causes the O side of this molecule to be negative, and the H side, to be positive. Here are some pictures of Polar Molecules...

Liebs did a demo to show the polarity of water. He had a balloon and he rubbed it against his head. This caused the balloon to take a negative charge. There was also a stream of water dripping from a glass cylinder. When liebs put the balloon close to the water, the water bends towards the balloon. What actually happens is the positive side of the H2O molecule (the H side) is attracted to the balloon. Hopefully now you know more about polar and non polar molecules....

The HW is to make sure you are keeping up with the webassigns

Polarity

A polar molecule is caused caused when the difference in the electronegativity of an atom is between .4 and 1.7. If the difference is between 0 and .4 then the molecule is not polar. In a non-polar molecule the electrons are equally shared between the two atoms that are bonded together. in a polar molecule the electrons are unevenly shared between the atoms that are bonded together. In the bond one of the atoms tends to be negatively charged and the other tends to be positively charged.

One example of a molecule that is not polar is C-C. This molecule is non-polar because the difference in electronegativity of the two atoms is zero.

An example of a polar molecule is C-F. This molecule is polar because the difference in electronegativity is 1.43. Since it is polar the fluorine atom pulls harder on the electrons in the bond then the carbon and thus is partially negative while the carbon is partially positive. The electrons in this covalent bond are still being shared just not 50-50 between the two atoms.

The next scribe is.....Amar B.

Building the Big Ones

Today in class we did our first lab of the new unit. This lab was show students what a molecule with more then one central atom would look like. The molecules we had to build in the lab were, ethanol, acetic acid, serine, and styrene. Each molecule has a very unique shape to it and has many central atoms. In the pictures below black represents a carbon atom, yellow is hydrogen, red is oxygen, and blue is nitrogen.

This atom is ethanol and is comprised of two carbons, six hydrogens, and one oxygen, with the carbons and oxygen being the central atoms.

In this photo is the acetic acid molecule. It is made up of two carbons, four hydrogens, and two oxygens. In this molecule the carbons and one of the oxygens are the central atoms. Also in this molecule the metal springs connecting the carbon and oxygen atoms represent a double bond.

This molecule is serine. It has three carbons, seven hydrogens, three oxygens, and one nitrogen. The three carbons, two of the oxygens, and the hydrogen are the central atoms.

The final molecule is styrene. This molecule has eight carbons, and ten hydrogens. All eight of the carbons are central atoms.

VESPER 2

Before I begin I just want to thank to Chris that he made me scribing tonight. This is so fun....

Today we learned VESPR of five and six electron pairs

for five electron pair, there are three type of possible shapes they can be

The first one we learned today was

Trigonal-bipyramid

known example as PF5

does not have nonbonding electron

somehow I can`t put picture sorry

next

C-saw

ex; SF4

has one nonbonding electron

T-shaped

ex; ClF3

has two nonbonding electrons

those are five electron pairs

and

here is six electron pairs

Octahedral

does not have any nonbonding electron

known as SF6

square pyramid

has one nonbonding

ex; ClF5

square planar

has two nonbonding electrons

ex; XeF4

liner

has three nonbonding electrons

ex; XeF2

here is the list

this might have some extras but doesn`t matter

thank you and next scribe will be..... TREVOOOOOOOOR brrroowwn

have funnn

Valence Shell Electron Pair Repulsion, and how it affects the structure of Atoms.

To start off, we need to make clear that electrons always come in pairs, and that their are two different types of pairs.
1.The first of these are Bonds.
2.The second are Non-Bonding pairs.
Both of these will affect the Structure of our molecule, but the only part of the structure we see are the bonded Pairs. This will make more sense whence you understand the Valence Shell Electron Pair Repulsion (VSEPR) rule. Under VSEPR electrons pairs in the outermost shells will attempt to go as far away from each other as possible. This means that although we don't look at the Non-Bonding electrons in the structure, they still are Under VSEPR and are effecting the shape of the electrons.
Although it is called Electron Pair Repulsion, we are not simply looking at the pairs, we are looking at areas of electron. I mean to say that if we were to encounter a double bond between two atoms, we would not expect the two pairs involved in the bonding to repel each other. No, these Double Bonds and triple bonds stick together.
In drawing the shape of Atoms we look at the number of Electron Areas around the Central Atom. A different structure is given based on how many electron Area's are around the central Atom and how many of these Areas are Bonds or Non-bonding Pairs. The Notes did a very good job of going through these types but because I do not have access to them, I'll go through it with you now.

Linear is the structure given when their are only two Electron Areas surrounding the central atom and both are Bonds. The atoms are exactly 180 degrees from each other. This structure looks like this

Trigonal Planar this structure happens when the central atom has three electron Areas and all three are Bonds. The atoms still all fit on a plane and are all 120 degrees from eachother. This structure looks like so

Bent Molecule This happens when their are only two Bonds, like Linear, but the central atom also has A non-bounding pair. This causes the atoms to remain 120 degrees from eachother but we only see two of the atoms, and we see a bent structure like this

Tetrahedral Molecules get a little more complex because they now become three dimensional. When their are four electron areas, the atom seperates every atom by 109.5 degrees to look like so

or when drawn on paper it looks something like

Triangular Pyramid when one of the four electron areas is a non-bonding pair it looks something like this

If two of the four electron ares are Non-Bonding then we see another Bent Structure, but in this case it is slightly more tight of an angle creating about a 104 degree bent.

Well there you have the atom structures that we have learned so far. No homework tonight but try to keep on track of upcoming webassigns. thank you, the next scribe will be
Takashi, have fun.

Where are all my electrons?

When drawing lewis structures we may sometimes run into a problem. One such problem arrises in the drawing of SO2. SO2 has one single bond and one double bond. We could just give one Oxygen Atom a single bond and one Atom a double bond, but this would not be accurate. The reason is because the electrons that form these double bonds are constantly vibrating between the two Oxygen Atoms. A more appropriate way to draw the Lewis structure would be using it's resonance structure, which looks like so


A double headed Arrow separates the two lewis structures letting us know that if we were to take a snapshot of the atom at any given time, it would look like one of these two diagrams.

One other point brought up in class today was Ions. Ions are slightly more complex to draw in a Lewis, structure, but fortunately not too complex. Their are two main steps that are need to remember.
1. The first is that the molecule is not neutral and therefore has either more or less electrons. If the Ion has a charge of 2-, then it has two extra valence electrons.
2. The second difference between these and neutral molecules is that you must bracket in your entire Lewis structure and write the charge of the Ion outside of the brackets at the top right, as you would for a power of.

To put both lessons together, the following shows the Resonance structure of the Ion NO3(-)