Polar Molecules

  In polar molecules, there is an overall separation in charges. An important aspect in determining whether a molecule is polar or non-polar is to look at its diagram and see if there is any symmetry. If a molecule is unsymmetrical, it is usually polar and if it is symmetrical, it would usually be non-polar. If one was to figure out that the molecule was non-polar, that would mean that the pull of the electrons is usually balanced. After determining if a molecule is polar, that would mean that the molecule has either different atoms or a different amount of atoms. One would then use signs to show which side is partially positive or partially negative.

EX.1:

ION CONCENTRATION:

HCl---> H+1 + Cl-1 [dissociation]

Dissociation:
1. Ionic compounds are made up of two parts:
    - cation: positively charged particle
    - anion: negatively charged particle

2. When ionic compounds are dissolved in water, the cation and anion separate from each other

3. This process is called dissociation

4. When writing dissociation equations, the atoms and charges must balance

5. The dissociation of sodium chloride is:
     NaCl---> Na+ + Cl-
ex: 1. Fe[OH]2=---> Fe+2 + 20H-1
      2. Na3PO4=---> 3Na+1 + PO4-3
      3. Fe3[PO4]2= 3Fe+2 + 2PO4-3
      4. If the volume doesn't change then the concentration of individual ions depends
          on the balanced coefficients in the dissociation equation
          a. Determine the {Na+} and {PO4}-3 in a 1.5M solution of Na3PO4
          Na3PO4 [1.5M]---> 3Na+[4.5M] + PO4-3[1.5M]
1.5mol/L x 1/1= 1.5mol/L

6. Determine both ion concentrations when a 2.5M solution of lithium sulfate dissociates
    Li2SO4[2.5M]---> 2Li+ + SO4-2
    {Li+}= 5.0M
    {SO4-2}=2.5M
     ZnCl2[0.376M]---> Zn+2 + 2Cl-1[0.752M]
7. A 100ml solution of 0.500M PcCl2 is added to 200ml solution of 0.100M
    NaOH. Determine the final concentration of each ion
    PbCl2[0.500M]--->Pb+2[0.500M] = 2Cl-1[1.00M]

c1v1= c2v2
[0.500M][0.100L]= c2[0.300L]
c2= 0.167M= [Pb+2]
c1v1=c2v2
[1.0M][0.1L]= c2[0.300L]
c2=0.333M=[Cl-1]
c1v1=v1v2
[0.100][0.200L]= c2[0.300L]
c2=0.0667M= [Na+] = [OH-1]
        

Titrations

-A titration is an experimental technique used to determine the concentration of an unknown solution.

Terms and Equipment
- Buret contains the known solution. Used to measure how much is added.
- Stopcock valve used to control the flow of solution from the the buret .
- Pipet is used to accurately measure the volume of unknown solution.
- Erlenmejer Flask contains the unknown solution
- Indicator is used to identify the end point of the titration.
- Stock solution is the known solution.
http://www.youtube.com/watch?v=9DkB82xLvNE

Dilutions

  It is evident that when two solutions are mixed, the concentration (measured in mol/L) changes. In the process of dilution, the concentration is decreased by adding a solvent, or any substance that dissolves another substance (usually water.) Similarly to how one adds one cup of water to one can of juice concentrate, or how one adds one cup of water to one can of soup, the substance that is dissolved (solute) does not change in amount. This could be explained with the equation:

n1 = n2    ->    c1v1 = c2v2

 Where c=Concentration, n=number of moles, & v=volume.

EX.1:

Determine C when 200 mL of 0.30 M of Sodium Nitrate (NaNO3) is diluted to a final volume of 600 mL.

1. Remember to first convert mL to L as M is measured in mol/L. After doing so, write out your equation that explains the conservation of the solute before and after dilution.

200 mL  x  1 L    =    0.200 L                     600 mL  x  1 L    =    0.600 L

              1000 mL                                                  1000 mL

c1v1 = c2v2

2. With the information you are given in the question, plug in the numbers into your equation and isolate the variably you are looking for.

(0.30)(0.200)  =  C2(0.600)

                                                                    (0.600)           (0.600)

3. Once you have isolated your variable, calculate & answer the question with correct amount of significant digits.

(0.0600)  =  C2

                                                                                                (0.600)

                                                                       0.10 mol/L = C2

In order to answer other questions similar to this one, you have to consider what is it that the question is asking you to find? In most cases you will have to isolate the variable of which you are solving for.

For more examples on this topic, check out these links:
http://misterguch.brinkster.net/PRA025.pdf

http://www.youtube.com/watch?v=ygr0CGdkAws

Titration Lab

Hello fellow subscriber to this blog!

Today we did a lab on titration. 

We used Vinegar CH3COOH

 and as well as Sodium Hydroxide NAOH

We tested to see the concentration of the vinegar using sodium hydroxide and also 2 drops of Phenolphthalein

We carefully measured how much sodium hydroxide can be poured into vinegar to make it fully "pink". It was cool how every drop it shows a bit of pink then goes away. 

BUT!

To be the MASTER OF TITRATION [kinda sounded cooler when Mr.Doktor said it]

It only takes one drop...

Yes one drop to make it all pink.

Like this :)

Well that is all that we did so stay tuned for our next lesson (: