Chem Class- April 30, 2010

New unit:
ORGANIC CHEMISTRY
- There are more carbon compounds than all ionic compounds combined
- The study of carbon compounds is called organic chemsitry
- Carbon can have multiple bonds and form many different shapes

Hydrocarbons have three types of formulas:

1) Molecular formulas
C6H14

2) Condensed Structural Formula
CH3-CH2-CH2-CH2-CH2-CH3

3) Structural Formula

Nomenclature of Hydrocarbons
- One molecular formula can have a number of different structures
- Isomers are compounds that can be drawn in more than one way

Naming Alkanes
1) Name the longest chain by using the correct suffix and adding "ane"
2) Locate any branches by number carbon atoms (use the lowest possible number system)
3) Name branches by using appropriate suffix and -yl ending (Alkyl branches)
4) If there are more than one of the same alkyl group, number each one and add the multiplier number in front of the branch name

Chem Class - April 22, 2010

Ions in Solutions
- The formation of a solution depends on the ability of the solute to dissolve in the solvent
- Solvation is the interaction between solutes and solvents
- Ionic solids (salts) are cyrstals made up of ions
- Molecular solids are crystals made up of neutral molecules
- Dissolving ionic solutions produces ions in a process called disssociation (remember?)

Ionizaiton is the break up of a neutral molecule into charged particles
Examples:
1) FeCl3 (s) ----->Fe 3+ (aq) + 3 Cl -1 (aq)
2) Ag2O (s) -----> 2 Ag + (aq) = O 2- (aq)

3) Na3PO4(s) -----> 3 Na + (aq) + PO4 (aq)

4) (NH4)2SO4 (s) -----> 2NH4 + (aq) + SO4 2- (aq)

Determining concentrations is relatively easy.

Examples:

What is the [Cl-] in a solution of 0.50 M AgCl3?

AgCl3 -----> Ag + (aq) + 3Cl- (aq)
Cl = 3x as many moles = (0.5 M) x 3 = 1.5 M

What is the [NO3-] in a solution of 0.82 M Fe(NO3)2?
Fe(NO3)2 -----> Fe 2+ (aq) + 2 NO 3- (aq)
(0.82 M) x 2 = 1.64 M

What is the [Cr2O7 2-] and [K+] when 3.5 g of K2Cr2O7 dissolved in 40 mL of water?
K2CrO7 -----> CrO7 2- (aq) + 2K + (aq)
3.5 g x 1 mol/294.2 g = 0.0

Here is a video showing the dissociation of salt:

Chem Class - April 20, 2010

Intermolecular Bonds
- bonds between molecules
- 3 types

1) London Dispersion Force (L.D.F)
- Results from temporary electron dipoles
- Weakest intermolecular force
- Increases as the $ e- increases
- Occurs in any compound that has e- (ie: everything)

2) Dipole-Dipole
- Results from a permanent dipole in molecules
Polar molecules experience this force
Polarity depends how much elements want e- (electronegativity)
- Electronegativity increases to the right and up
- The strength of a dipole- dipole  bond depends on the difference in electronegativity between the two atoms
- Only polar molecules experience this

Substance          Boiling Point              # of e-
N2                     -196 degrees C          14
O2                     -183 degrees C          16
NO                   - 152 degrees C          15
ICl                       97 degrees C            70
Br2                     59 degrees C             70

(The more electons, the higher the boiling point. The type of intermolecular bond also plays a role.)

3) Hydrogen Bonnds (H-bonds)
-This is a special type of dipole- dipole bond between H and O, F, or N
- Any molecule that: H-F, H-O or H-N

Identify the substances with H-Bonds:
1) CH4
2) CH3OH
3) H2S
4) CH3-NH2
5) HCl
6) CH2-OH-OH2
       /      /       /
    OH  OH  OH

Answer: Number 2, 4, and 6

Compare the boiling points of:
- Ethanol (C2H5OH)
- Ehtane (C2H6)
- Methanol (CH3OH)
- Methane  (CH4)

The actual boilingpoints: Ehtanol = 78 degrees Celcius, Ethane= -89 degrees Celcius, Methanol = 65 degrees Celcius and Methane = 161 degrees Celcius. Remember London Forces are the weakest intermolecular force and hydrogen bonds are the strongest. Also, the more electrons, the higher the boiling point.

Chem Class - April 16, 2010

Today we...

- Went over our homework
- We did a lab based on 'polarity'
               - Before that, however, we did some notes:

Solvents and Solutes can be Polar or Non-polar
Non-polar substances have equal charge distribution (symmetrical)
Polar substances have an unequal charge distribution (asymmetrical)

H2O = polar:

CH4 = nonpolar:

_________________________________________________________

The lab's objective was to determine if Glycerin is polar or non-polar.

Here's the background information that was written on the lab:

- Sodium chloride is an ionic solid crystalk that forms a crystal lattice structure. When dissolved in solvents, this lattice breaks up and the ions dissociate.

- Sucrose is table sugar and like Sodium Chloride it also forms a crystal structure. Unlike Sodium Chloride however, Sucrose is not ionic; it is molecular. The structure of Sucrose makes the molecule polar.

- Iodine, like Sucrose, is molecular and also forms crystals. However the crystals of Iondine are non-polar.

- Water is a polar solvent

- Paint thinner is a non-polar solvent

- Glycerine is a polar solvent

The materials we needed were test tubes, test tube stoppers, a test tube rack, scupula, safety goggles and an apron, sodium chloride, sucrose, iodine crystals, paint thinner (Turpentine) and Glycerin

The entire procedure basically involved us seeing whether or not the solutes (like table salt, sugar and iodine) dissolved in the solvents (water and paint thinner). We learned that polar solutes dissolve in polar substances and non-polar solutes dissolved in non-polar substances (LIKE DISSOLVES LIKE)

Chem Class - April 14, 2010

Today we finished our test, and finished our conductivity lab by finding the conductivity of water. Distilled water on its own is not conductive, but as soon as we add salt (ions) the conductivity increases.

Electrical conduction in solutions requires charged ions to be present.
Ionic solutions dissociate (break apart) when placed in water. Molecular solutions do not usually split into ions
The following is the dissociation of sodium chloride:

Follow these steps to determine conductivity:
Is it a metal?
If yes it is conductive. If no ask...
Is it a solid non-metal?
If yes it is non-conductive. If no ask...
Is it an acid or base?
If yes it is conductive. If no ask...
Is it ionic?
If yes it is conductive. If no it is non-conductive.

Here is a video on electrical conductivity, demonstrating that ions must present in solution for electrical conductivity:

Chem Class - April 1, 2010

Today we had just enough time to do a lab that involved testing the conductivities of different solutions.
Here's our results (Just by looking at the table you can see that ionic solutions are more conductive than molecular solutions):