Select Page

Q3: Week 6  – 3/14 – 3/18

                                                                                                                                                                                 Jump to:  Tuesday,   Wednesday,  Thursday,  Friday                                                                                                              ______________________________________________________________

3/14 – Monday – B Day – 2, 3b/4 Lab

Main focus –                                                                                                                                                         
                                                  

    a) To introduce MO theory, a non- valence bond theory.

    b) To complete a MO diagram.

    c) To compare BO, bond lengths, and bond energies by MO diagrams.

Period 2,  3/4:   

1.  Review the need for another theory other than the valence – bond theories that we have been studying

      a)  Mo Presentation – modeling Diatomic homonuclear MO Diagrams
 

2.  Selected correlation graphs (Li2 – C2) – These were in the student presentation “MO Bonding “

 
bonding 5a MO Yo classwork!.pdf
View Download
 
Used this worksheet after the “MO Bonding”
bonding 5 MO Yo! oxygen and nitrogen.pdf
View Download

 

MO – N2 vs N2+.pdf
View Download

3.  Review Last nights Form: 

MO Theory Form 1920 – Key p.pdf
View Download

   

MO and Gap Theory:

_____________________

TODAY’s NOTES:

 
Class Notes on the limitations of the Valance Bond Theories:
 
Valence bond theories that we learned:
1: Covalent bonds – sigma, pi bonding
2: VSEPR theory – (electron orbitals repelling to form equidistance stable geometries)
3: Lewis Dot structures
4. Hybridization
 
 
Our valence bond theories = hybridization, VSEPR, Lewis dot diagrams have limitations as we have seen.  How does the chlorate ion have resonance if it is sp3 hybridized and there are no un-hybridized p orbitals to pi bond with?
 
Remember that dots on a piece of paper can give us so much information for many molecules some complex but some our rules of formal charges that help guide us to the best structure guide us to structures that actually do not exist based on their properties found experimentally!
 
Here is an example of the sulfate ion, SO4-2
 
THE LEWIS DIAGRAM BELOW REPRESENTS THE BEST LEWIS DOT STRUCTURE BASED ON FORMAL CHARGES.  Below each sulfur has a Formal charge of ZERO!
Above is what our valence bond theory predicts using the rules of Formal Charges and etc.  THIS IS NOT WHAT WE FIND experimentally!!! Actually the lewis diagrams that we find from experimental evidence looks like the following.
 
The sulfur below has a Formal Charge of +2 and yet it is the structure we identify experimentally!
 
WHAT???  How can it exist more like this structure when clearly is breaks the rules of Formal Charges (+2) on the Sulfur atom?  Actually the charge is measured to be +1.77 on the sulfur in experiments.  What gives?  The bonding is neither covalent nor ionic it is something in between.. 
 
So we are at the end or the limits of this valence bond theory. We were were always going to be limited by theories that treats electrons as dots when we have learned that electrons exist as waves!!!
 
OK so what if we run into a Lewis Diagram that is beyond the Valence Bond Theory?
The Current AP Curriculum does not support using Formal Charges to provide guidance in building lewis dot diagrams that are beyond the Octet Rule.  The rest of the world does so we make the following rule when dealing with AP:
 
If there is a element that exists in row three and beyond then the octet rule takes preference:
Does experimental evidence support this rule completely? No.  Does experimental evidence support the use of formal charges completely? No.  We need a new theory!
 
Example:  SO4-2  , SO3
So lets learn a new theory that picks up where valance bond theory leaves off.  It is called MO theory or molecular orbital theory and it treats electrons as waves!                                                                                                                                                                    

That Theory is MO Theory!  

 

____________________

3/14 – Monday Homework: –                                                                                                                                                                                                                           

1: Please view the MO Theory to Band Theory lecture below.

2:  Please complete the Gap or Band Theory Form below: 
 
 

MO theory to Band Theory:

 

 
4 : Gap or Band Theory Form 21-22

>

 _________________________________________________________________________________________________________________________

3/15 – Tuesday – A Day – 2/3a Lab, 4 

Main focus –                                                                                                                                                         
                                                  

    a) To identify the different properties of the Ionic, Molecular, Metallic, and Network               solids.

    b) To Compare and contrast LDF, dipolar forces, and H-Bonding IMF’s in Molecular               Solids.

 

 Period 2/3 4: 

1. Homework Review of the MO Theory Form and Gap or Band Theory Form

 
MO Theory Form 1920 – Key p.pdf
View Download
 
Gap or Band Theory Form Key p.pdf
View Download 
 
IMF FRQ – 2013 – question 6 – AP Central Key
 
2.  Types of Solids through presentation: Whatever theory.
 
        Gap theory –   Size of gaps between electron energy levels that explain electrical conductivity
                                    or the lack (large gaps) AND absorption of light (pigments).
 
        Pi stacking = delocalization that allow delocalization of electrons through metallic 
                                  and SOME molecular compounds. Creates smaller gaps between energy levels.
 
        network solids  – molecular compound with a continuous crystal
 
        Diamond vs Graphite – type of network solids that have differ based on pi stacking
 
        chromophores – molecular compounds that have delocalization that are pigments.
 
         crystal field theory –   remember me?
 

– see the chart in the NOTES section

 

Types of Solids.pdf
View Download
 
Types of Solids key.pdf
View Download
 
3. INTERMOLECULAR FORCES  LESSON – 
     

_____________________

TODAY’s NOTES: 

Network solids are the RARE CASE when some molecular compounds make continuous covalent bonds in their crystals.  Diamond and Graphite are examples.  Most molecular solids are held by IMF. *Graphite is the only Network solid that conducts due to the delocalization of electrons throughout its crystal.  

 

 

IMF = Intermolecular Forces – ATTRACTIVE forces that hold molecules together
 
Molecular solids have the lowest melting points because when you give them heat you are separating molecules HELD TOGETHER BY ATTRACTIVE FORCES (IMF) that are only a fraction of the BOND Energy of Covalent, Ionic, or Metallic BONDs!  It takes less energy to separate molecules held together by attractive forces than it does to separate atoms or ions (breaking bonds).
 
Since we are breaking only attractive forces AND NOT BONDS heating this solid would be a PHYSICAL Change as the chemical formulas (of the individual molecules) would not change!
 
All phase changes (ex. melting, freezing) of molecular compounds are always physical changes!!!!
 
                                                      H2O (s)  —-> H2O (l)  —-> H2O (g) 
 
                                                               Ice     —->  water    —->  steam (can’t see it!!)
 
We are only separating the attractive forces between the molecules and thus the chemical formula does not change.
 
In our copper Iodine lab earlier in the year why did the Iodine sublime?
                                                                        
                                                                                                                                 I2 (s)  ——>   I2 (g) 
 
Because Iodine is a molecular solid with a low melting (sublimation) point due to the weak attractive keeping iodine as a solid.                        
 What caused the atmospheric Oxygen become a liquid? What forces are at play? 

 

                What held the molecules of polyvinyl chloride together in SLIME (Holiday Cross Linked polymers)?

 

Intermolecular Molecular Attractions: (IMF’s)

____________________

3/15 – Tuesday Homework: –                                                                                                                                                                                                                           

1. Complete the Types of Solids.pdf worksheet and review with the key.
 
Types of Solids.pdf
View Download
 
Types of Solids key.pdf
View Download
 
2.  View the Lecture on the Intermolecular Forces (IMF’s) below. (You may not need to view if what i did live in class today was enough)
      Remember that these forces are the forces that keep molecules together as a solid or liquid. They are are also the forces that make gases deviate from Ideal Gas behavior.  They are also are the reason each compound as a liquid has a unique vapor pressure and boiling point.
 
3. Complete the Form below on identification of the IMF’s in the molecules below:
 

 

    2 : Intermolecular Forces Lecture:  

 

 
3 : Intermolecular Attractions Form 21-22

>

___________________________________________________________________________________________________________________

3/16 – Wednesday – B Day – 2, 3b/4 Lab

Main focus –                                                                                                                                                         
                                                  

    a) To determine the solubility of molecular compounds by identifying IMF’s

    b) To determine the difference in individual IMF’s in molecular compounds.

    

Period 2 3/4:  

1. Quick Review of the Types of solid worksheet –  IMF’s are between molecular solids!
 
Types of Solids key.pdf
View Download

 

2. Review of the Last nights Intermolecular attractions Form – 
Intermolecular Attractions Form 1920 – Key.pdf
 
a) You must think about the IMF’s between the same molecular compound – boiling points, vapor pressure
b) You must think about how each molecular compound will interact with water – micibility, solubility
 – If a molecular substance has similar IMF’s with itself as water has with itself then it will be soluble with water.  How does a molecular substance mix with water?  It must make it easy for water (solvent) to let go of its own attractions and make new ones with the molecular substance (solute).  The more similar the IMF’s the easier can water and dissolve and make a homogeneous mixture = solution.
The most soluble in water = the molecular compound that has the most similar IMF’s  as water has with itself.
The least soluble in water = the molecular compound that has the least similar IMF’s as water has with itself. 
3. Complete the IMF presentation to compare molecular compounds 
4.  Molecular – ion attractions – Dissolving salts (ionic compounds)
     Molecular  – dipole attraction – Dissolving of molecular compounds 

 

“Like dissolves like”. is not completely accurate.

 Tinctures vs. Aqueous 

Sucrose: 
 

phenolphthalein:

 

TODAY’s NOTES:                                                                                   

REMEMBER the Slime (Cross-Linked Polymer) activity?  The long strands of the top and bottom molecules are held by the middle molecule attracting them. Notice the dashed lines in between the three molecules shown that represent the attractive forces.  Each different molecule is circled. These dashed lines are Intermolecular Forces (IMF’s) that are keeping this SLIME together as a solid.  They are written as dashed lines so not to confuse them with bonds. Because this solid is held by IMF which are much weaker than bonds you can imagine that it would not take much heat to “melt” your Slime. It would have a very low melting point.

 

Intermolecular Molecular Attractions: (IMF’s)

______________________

3/16 – Wednesday Homework: – 

 
* You can expect a FRQ on this topic tomorrow in class – 15 minutes timed. 
 
1: Complete the IMF comparison worksheet 1819.pdf worksheet using the 
      Lecture below for the worksheet.  The key is available for your viewing pleasures.
      The key is helpful but the lecture is more important!
 
IMF comparison worksheet 1819.pdf
View Download 
 
IMF comparison worksheet 1819 KEY.pdf
View Download
  
2. Complete the IMF comparison 2 worksheet.pdf for more practice on IMF’s
      with the key or the video below it.
 
IMF comparison 2 worksheet.pdf
View Download
 
IMF comparison 2 worksheet Key.pdf
View Download

    1 : IMF worksheet review:  


 

    2 : AP Chemistry IMF worksheet review: 

This was a lecture made with the older version of the worksheet that you have.
I updated your worksheet to show the actual structural formulas.

 

_________________________________________________________________________________________________________________________

3/17 – Thursday – A Day – 2/3a Lab, 4 

Main focus –                                                                                                                                                         
                                                  

    a) To practice an FRQ on IMF’s

    b) To introduce the concepts of Chromatography

 

Period 2/3:  – 

 
1:  FRQ practice – 15 minutes timed.
2.  FRQ review:
 
IMF FRQ – 2013 – question 6 – AP Central Key
 
3.  Molecule – ion vs Molecule – dipole  attractive forces in solutions
4. TLC of Universal Indicator – pre -lab
5. Run the lab

 

 

Period 3/4:  – 

 Same as above except we will not Run the lab till tomorrow

 

______________________

Lab 22 – TLC of Universal Indicator

 

TLC of Universal Indicator
View Download 

In this lab we will perform a physical separation technique based on the solubility of the individual components in a mixture.

This is Lab will be a slide-up.  I would like for you to write a background on how TLC works and relative strength of the different IMF’s in the molecular compounds (chemical indicators) that make up a industry standard mixture called Universal Indicator.
 
Universal Indicator Acid/Base Indicator that has a unique color for each pH value:
 
 
A lot of pool kits that measure pH use Universal Indicator!
Universal Indicator can accomplish this broad range of colors because it is a homogeneous solution of three Acid/base indicators (CHROMOPHORES!!!!!!!!!!!!) that change their amount of conjugation based on the concentration of available protons (H+) or hydroxides (OH–).
 
Also do not forget the acid/base indicators ARE CONJUGATE ACID and CONJUGATE BASE solutions which are Buffer solutions.
 
                                              HIn                             —->                            H+           +         In–
 
                             Conjugate Acid                                                                                      Conjugate Base
                                 one color                                                                                                 New color
 
  Phenolphthalein is an example:
There are slightly different types of Universal Indicators that use slightly different mixtures of indicators. We will using the BOGEN Universal Indicator mixture.
 
Bogen Universal Indicator Mixture:                      1.  Methyl Red                       pKa = 4.95
                                                                                         2.  Bromothymol Blue         pKa = 7.1
                                                                                         3.  Phenolphthalein             pKa = 9.4
 
So the colors of each pH from above are due to the mixture colors of each indicator at a certain pH levels:
                                                                                                 (negative theory of light)
 
Okay so the point of this lab it separate each of these 3 individual molecular substances by using TLC (Thin Layer Chromatography).  Thin Layer Chromatography is another physical way we can separate mixtures. 
 
– We have separated homogenous mixtures before using evaporation in the carbonate lab where we added HCl to an unknown white powder (that was either NaHCO3 or Na2CO3) and created NaCl (aq) and CO2 that left as bubbles.  We boiled off the water (separated the H-Bonds of water) and obtained dry NaCl (s) which we used by stoichiometry to determine our unknown. Connections!!!!
 
– we also studied distillation (of Coca-Cola) as another physical separation technique of mixtures!
 
– we also used filtration of a precipitate to separate a mixture in our gravimetric titrations!
 
Remember that solutions are mixtures that are soluble that are held together by IMF’s!  When we separate a mixture it is a physical change because we are not breaking bonds we are ONLY BREAKING IMF’s between MOLECULES!!!
 
TLC just like all chromatography separates a mixtures based on the idea that in a mixture the individual molecules retain their individual properties since their chemical formulas are not changing in the process.  This means that each chemical indicator will retain their individual solubilities (their percentage of non-polarity due to the amount of predominant LDF forces or their percentage of polar nature due to the amount of dipolar and H-boding) in the mixture. 
 
Thus in TLC we will separate the 3 acid/base indicators by their solubility to either a mostly non- polar solvent (mobile phase – hexanes) or polar solvent (stationary phase – Silica Gel).  
 
We will spot a TLC plate with Universal Indicator in a starting position close to the bottom of a Silica TLC plate (stationary polar phase) and add a liquid solvent – hexanes (non-polar mobil phase) that move up the Silica TLC plate by capillary action.  When the solvent reaches the “spot” or mixture EACH component of the mixture, 
 
Methyl Red, Bromothymol Blue, and Phenolphthalein will have a choice to either stay with the polar Silica Gel on the TLC plate or move with the non-polar mobil hexanes.  BASED on their individual molecular structures (that define the IMF’s that they have), each chemical indicator will have a unique amount of polar or non-polar characteristics AND they will each move a unique distance up the TLC plate.
 
– If one of the chemicals is more polar (have stronger dipolar forces or have H-bonding) than the other three than they will prefer the Silica TLC plate and MOVE LESS than the other chemical indicators of the mixture that must have more non-polar characteristics.  
 
– The chemical indicator that is the most non-polar (have mostly LDF’s with less dipolar forces), would prefer to be attracted to the mobile non-polar hexane solvent and thus move up the plate more.
 
*Remember this a separation technique based on solubility. Solubility is based on how similar the IMF’s have with the mobile non-polar solvent (hexane) or the polar stationary solvent (TLC silica Plate). Look at the two solvent molecular structure above to identify what IMF are most similar with each solvent! 
 
The distance that the individual chemical indicators move compared to the original spot will be measured.  
 
 
Yellow layer – Carotenoids – 
 
 
Green layers – Chlorophyll A and Chlorophyll B – is one slightly more polar?
 
– Notice these pigments are chromophores!!!
 
– There were three layers separated in the Time Lapse Chromatography below.  Looking at the pigments separate in the video below, and the molecular structure above can you identify the chemicals in the chromatograph? Why was the yellow layer almost at the top while the 2 green layers barely moved at all?
 
– Also notice that we did not spot this TLC plate, we rolled a coin on a spinach leaf unto the TLC plate to make line. The green line was our starting point. 
So the assignment is to rank the polarity and non-polarity of the three chemicals in the mixture of Universal Indicator based on what you know of IMF’s AND Predict which chemicals will travel the greatest distance up the TLC plate and which chemicals with travel the shortest distance.  This discussion is the subject of your Background of the lab. Use these structural formulas in your Background.
THEN Write a hypothesis based on your background.
 
Hypothesis Example: Chemical A will have the largest Rate of Flow (move the farthest on the TLC plate) while the Chemical B will have the smallest Rate of flow.
 
Bogen Universal Indicator Mixture:                      1.   Methyl Red                      pKa = 4.95
                                                                                         2.  Bromothymol Blue         pKa = 7.1
                                                                                         3.  Phenolphthalein             pKa = 9.4
 
Methyl red:
Bromothymol Blue:
 
Phenolphthalein:
 

 

     

 

_____________________

3/18 – Thursday Homework: – 

 
1.  Complete the Form below.  Make as many submissions that you need to get a 100 but be aware every extra submission will cost you 10 points. For example if it takes you 3 submissions to get a 100 you will get a 70.
 
Tonight you will accomplish 2 things in the Google Slide Presentation that I sent you today.
 
2.  Write a background on the TLC of Universal Indicator Lab.  
        This will be our last formal lab write – up.  You will have an email with the link to your shared doc to begin this lab.  The focus of your background MUST include a comparison of the polarity and non-polarity of the three chemical indicators in Universal Indicator.  This comparison must include a discussion of the IMF’s of the three chemicals using diagrams of their molecular structures.  Thus your background must include molecular structure that you should search for and place in your background. The whole purpose of the background is to develop a your argument or your position on whether which chemical indicator is the most polar and non-polar. 
 
3.  Write a Hypothesis based on your position established in your background.
        Basic Format: If the independent variable does this the dependent variable will do that .
 
           The Dependent Variable is the distance the indicator moves up the TLC plate.
 
                            We will measure that distance by a calculation called Rate of Flow = Rf
 
For those that had me last year in AP Biology we separated the different pigments in the photosystems in the chloroplasts in spinach leaves.  We were able to separate three different pigments (CHROMOPHORES!!!!!!!)  in that lab.
 
1 : IMF RAT Quiz

>

  _________________________________________________________________________________________________________________________

3/18 – Friday – B Day – 2, 3b/4 Lab

Main focus –                                                                                                                                                         
                                                  

    a) To perform the TLC experiment with Universal Indicator.

    b) To confirm which macromolecules have the least and the polar characteristics.

   

Period 2: 
1.  Continue with the Lab 21.  Spray NaOH to reveal the position of the phenolphthalein.  Measure the Calculate the Rate of flow.  Compare and contrast your predictions.  
2. – making of dry – Ice – deposition – JOULE-THompson effect – IMF’s!!!!!
3.  CO2 Demo – Universal solution and dry ice:
        warm water and Universal (green) plus few drops of .1 M NaOH solution- add solid CO2
        on overhead projector with light hole (from sunset demo)

 

4. Slides 1 – 15 of the Thermodynamics presentation AND fill in the notes that is missing in the note packet that I gave.

 – state functions, path functions, delta E         
 
THermo read along – Thermo notes.pdf
View Download                                                                                                                                                     

 
Period 3/4: 
1. Introduce the concepts of chromatography.
2.  Separate a mixture (universal indicator) using differences in solubility (chromatography).

                                                                                                                                                                                                                                  3. Calculate the Rate of Flow.  

– making of dry – Ice – deposition – JOULE-THompson effect – IMF’s!!!!!
4: CO2 Demo – Universal solution and dry ice:
        warm water and Universal (green) plus few drops of .1 M NaOH solution- add solid CO2
        on overhead projector with light hole (from sunset demo) 

5. Slides 1 – 15 of the Thermodynamics presentation AND fill in the notes that is missing in the note packet that I gave.

 – state functions, path functions, delta E 
           

TODAYS NOTES:   

– phase diagram of water and carbon dioxide:

 

Chromatography Concepts:

Time Lapse of the TLC of Universal Indicator – 

 

Thermodynamics: The end of it all!!!

Fire Syringe Demo – 


 

 _____________________

3/19- Weekend Homework: – 

1.  Please complete your slide-up of the TLC of Universal Indicator.  This is due Monday.  
     You can use the images in the presentation above or under Thursday.
                                                                      

      a) Background slides –   This is where you should have predicted the most/least polar molecules from the mixture based on the molecular structures posted above. You should have used those images to discuss which compounds in the mixture have more LDF’s and which one have more dipolar forces.  

        b) Hypothesis slide – based on your background write a hypothesis regarding which compounds in the Universal Indicator would have more polar characteristics (hydrophilic) and which compound has more non-polar (non-polar) characteristics.

        c) Data Slide: – Pictures of your chromatograph and your compounds have been identified and separated based on their colors (before and after) spraying with NaOH (strong base).

                i) Include rate of flow calculation and data for your three spots tested on your TLC plate.

                ii) Include the picture of the Chromatograph AFTER it was sprayed with NaOH

         d) Results Slide: Which compound in the mixture had the highest rate of flow (traveled further up the TLC plate) and which compound had the lowest rate of flow (traveled the least distance on the TLC plate). 

         e) Conclusion Slide:  Using the diagrams of the molecular structure in your background determine what part of the structure may have been responsible for the outcome on the final chromatograph.  Make sure you are discussing the IMF throughout and solubility. Tie in your background to help with this discussion.  Which compounds were more polar and which compounds were least polar?  

        e) Sources:   

 

2.  Please review slides 1 – 15 from the Thermodynamics presentation and fill in the missing notes in the note packet I gave out.  

THermo read along – Thermo notes.pdf
View Download  

 

 
2 : Thermodynamics Form 1

>