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## Q2: Week 3  – 11/29 – 12/3

11/29 – Monday – B Day – 2, 3b/4 Lab

Main focus –

a) To review the use of the Henderson – Hasselbach to answer point 3 questions.

b) To identify buffer solutions as conjugate acid /base pairs

c) To use the concept of pKa for indicators and buffer solutions.

Period 2:  Collect Lab 10, 11 if not handed in yet.

1. Review Lab 12 and complete in class.

2.  Verify all 5 points on the graph.

3.  Buffer lesson with bicarbonate ion using notes – Maybe

Period 3/4: Collect Lab 10 and 11 if not handed in already

1. Same as above including the buffer lesson

2. Start the homework prediction 2.

Today’s Notes:

 Strong Acid Strong Base ~Lab 10 pH = 7 @           equivalence only spectators that DO NOT ionize water Weak Acid  Strong Base~Lab 11, pH  >7 @ equivalence Conjugate Base produced reacts with water                                                     to produce OH- Strong Acid  Weak Base~Lab 12 pH  <7 @ equivalence Conjugate Acid produced reacts with water                                       to produce H3O+

 The  Blood buffers the blood pH so that you survive!!!  There are so many organic molecules that have acidic or basic properties that would cause death in our aqueous plasma (fluid part) of our blood. The main buffer in our blood that prevents large pH changes if the following conjugate acid base pair:    Conjugate Acid                      Conjugate Base            H2CO3            <—>          H+  +  HCO3-1   Neutralizes Bases                  Neutralizes Acids

The pKa of  H2CO3 = 6.1   The Ka of this week acid = 10 3.8   = 1.58 x 10-4

Blood is buffered at pH of about 7.4.  What is the ratio of conjugate base to conjugate acid in this buffered solution?

pH = pKa + log [A]/[HA]

7.4 =  6.1  + log [HCO3-1]/[H2CO3]

1.3 = log [HCO3-1]/[H2CO3]

10X to both sides of the equation

101.3 = [HCO3-1]/[H2CO3]

=    19.9     :      1        ratio

*Normal human blood has about a 20 : 1 ratio!

What would this look like on a titration curve?

Sodium Carbonate / HCl (weak base / strong acid Titration): The blood buffer!

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Lab 1 2 – Weak Base / Strong Acid Titration

In this Lab we were trying to determine the concentration of a the weak base solution using a KNOWN concentration of a STRONG Acid.  I tried to make a 0.30 M solution of the weak base but because my stock solution was diluted from time our actual titration will be a little different.

Thus 25.0 ml of a unknown M NH3 solution is titrated with a total of 38 ml of a 0.25 M solution of HCl

1: Determine the equivalence point of the titration. (Identify of the graph)
2: Determine the concentration of the weak base.
3: Determine the end point of the titration if phenolphthalein was used. (Identify on the graph)
4: Determine the halfway equivalence point. (Identify on the graph)
5: Confirm the final pH of the titration.
6: Confirm the initial pH of the titration. YOU CANNOT DO THIS STEP!!!!!!!(In the spring) but it will be lower than point 2
7: On the first 4 points of the titration curve (1 = initial pH, 2 = halfway equiv., 3 = buffer position, 4 = equivalence               point,) determine the percentage of the Conjugate Acid/ Conjugate Base / OH
8: Write the net-ion reaction.
9: Determine the Ka of the Acid.

10. Confirm the pH of point 3 when _____ml of acid was added to the weak base.

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11/29 – Monday Homework: –

1.  Graph a titration curve take home quiz. – Due Tuesday

You will plotting the graph of the titration using the  skills you have developed from Labs 10,11,  and 12.

a) Design a Titration that will reach the equivalence point when 30 .0 ml 0.15 M NaOH
is added to 20.0 ml of HF. A total of 50 ml of the titrant will be added.

You will need the Ka of the Acid = 3.5 x 10-4

b) You will have to estimate the initial pH (you need equilibrium skills that we will have in the spring to calculate).
c) You will have to estimate the equivalence point pH ((you need equilibrium skills that we will have in the spring).

The numbered objectives that must be numbered on your graph include:

1) Initial pH (estimated ph but not volume).
2) The half equivalence point
3) point on the graph when 20.0 m of the titrant is added (show work)
4) Equivalence point (estimated ph but not volume)
5) The final ph (show work)

You also need the:

6) Calculate the initial concentration of the HF (show work)

7) Net ion reaction of the titration

8) Equilibrium reaction at the equivalence that supports your estimated pH at point #4

9) from the following list of indicators AND their pKa’s Identify the most appropriate
indicator for the endpoint titration AND the ENDPOINT of the titration.

Indicator                                                                        Color Change pH                                                        pKa
 p-Nitrophenol 5.3 to 7.6 7.2 Phenol red 6.4 to 8.0 7.9 Thymol blue 8.0 to 9.6 8.9

Blank Worksheet:
Design a Titration with HF and NaOH new.pdf

Please use our last prediction titration to review:

Weak Base Strong Acid Prediction 21-22 key p.pdf

End of Monday!!!

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11/30 – Tuesday – A Day – 2/3a Lab, 4

Main focus –

a) To Review the 5 points of the Titration Curve through the take-home prediction

b) To Review the concept of buffer solutions

Period 2/3:

1. Review Take Home Quiz.
2. Buffer lesson
3. Start the Review Form:                                                                                                                                                                                                                                                                                                                                                      Period 4:
1. Review Take Home Quiz.
2. Start the Review Form:

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11/30 – Tuesday Homework: –

1. You are to complete the Test review form below.
which is a review of all the concepts you need to complete the the acid base test. It will not be graded.

Here is a Blank copy of the form you could print:

Acid Base Concept Review Form blank.pdf

2: Review your work in the form as it will automatically grade and send back a link to a handwritten key.
3.  Please Redo a worksheet (Acid base Lab Titration Graph Questions.pdf) the we completed almost 2 weeks ago.  Everyone struggled with it BUT if you redo it you will find it much more manageable now (I hope!). I it  gave it out in class. Please review with the key and or the video below:
Acid Base Lab Titration Graph Questions.pdf

Acid Base Lab Titration Graph questions Key p .pdf

Link to the Review video for the Acid Base Lab Titration Graph Question.pdf:  https://youtu.be/FnK3DBJIyp4
4. Study for test Wednesday using the ACID BASE STUDY POINTS posted below:

ACID BASE TEST STUDY POINTS:

1. Identify Arrhenius, Bronsted- Lowry , Lewis ACID Bases
2.  Ka Table – strengths of acid – You will be given this table
3. Identifying conjugate acid/bases.

Conjugate Acid Base Pairs and Complex ions new.pdf

Conjugate Acid Base Pairs and Complex ions new key p.pdf

4.  Identifying Strong Acids and Strong Bases.
5. Basic ph skills – converting to ph, converting  [  ] from pH, etc

Skills 1 – 5 are from the intro worksheets and BOTH RATS:

Acid and Bases Intro packet new.pdf
Intro Acid Bases Packet Key 1718 p.pdf

Acid Base RAT:    Video review Link:  https://youtu.be/00ayszfDfUg
Acid Base RAT 2:  Key posted below:

Acid Base skills RAT 2 1E011 key p.pdf
6. Neutralization problems (Pre- neutralization worksheet)

Acid Base Pre- Titration .pdf
Acid Bases Pre-Titration key p.pdf

7.  Strong Acid base titration skills – Lab 10 – video review link: https://youtu.be/cDTElHo-tqQ
a) How to complete lab 10 screencast:    https://youtu.be/4AVxVI3F-Qs                                                                                                                                                                                                                                                                                                                      8. Weak Acid/ Strong Base titration skills – Lab 11 – video review linkhttps://youtu.be/RzWHKQ2ZUjQ
a) How to complete lab 11 screencast:  https://youtu.be/NuEyx02XRYA
9.  Picking an appropriate indicator – video review link: https://youtu.be/eQhjbVqWoUY
10. Calculating the Ka from graph – video review link: https://youtu.be/_-xOHdk8_6I

Determining pKa and Indicators.pdf

Determine Ka and Indicator key p.pdf

11.  Writing Net Ion reactions

Stiochiometry 5a – Acid Base Reactions new.pdf

Stiochiometry 5a – Acid Base Reactions new Key.pdf

12. Review of the yesterday’s Graph a titration curve take home quiz:
Design a Titration with HF and NaOH key p new.pdf

1: ACID BASE TEST REVIEW FORM:

End of MondaY….

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12/1 – Wednesday – B Day – 2, 3b/4 Lab

Main focus –

a) Acid Base Test

Period 2:

1. Acid Base Test

Period 3/4:

1. Acid Base Test

2. Review of Acid Base Test

______________________

12/1 – Wednesday Homework: –

1.  Please review your graded test that will be emailed back to you today with the key posted below Or the Video                   Posted below.

Acid Base Test 1 Key.pdf

Acid / Base Test 1 Review Video:

_________________________________________________________________________________________________________________________

12/2 – Thursday – A Day – 2/3a Lab, 4

Main focus –

a) Acid Base Test 2

Period 2/3:

1. Review of test 1

2. Acid Base Test 2

Period 4:

1. Acid Base Test  2

______________________

12/2 – Thursday Homework: –

1.  Please Complete the Pre-Tum Lab Form Below: You will have 3 total submissions.

1: ACID BASE Pre – Tums Lab FORM:

End of Thursday….

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12/3 – Friday – B Day – 2, 3b/4 Lab

Main focus –

a) Lab 13 – (Formal Lab Write-up) – Lab note -taking – Lab design of a Back titration

Period 3:

1. Review of test 1

2. Note-taking for Lab 13

Period 4:

1. Review of test 1

2. Note-taking for Lab 13

3. Standardization of Strong Base with KHP

In Tums we are dealing with the active ingredient, calcium carbonate, CaCO3.  Watch out this antacid is an insoluble salt that is found in limestone (sediment rock) and sea shells AND CHALK!!!!   It is an antacid because of its basic anion, the carbonate ion, CO3-2 .  It is a base because it can accept 2 H+ ‘s (Bronsted-Lowry Base) or it can donate 2 pair of electrons (Lewis Base) to 2 H+ ‘s .

The reaction with carbonates involve probably the most important equilibrium reaction that we have in organic chemistry. Organic Chemistry chemical reactions that support and sustain life.  It specifically deals with the Carbon based molecules and the link to the carbon cycle, specifically CO2 (g) as the product of combustion and the reactant in photosynthesis!

The arrows up in the atmosphere are gas molecules of CO2 (g) while the other forms may be CO3-2 (aq), HCO3 -1 (aq), and H2CO3 (aq), or CaCO(s).

 In our oceans the movement of carbon through the marine ecosystem can be stored as calcium carbonate, limestone, sedimentary rock or it becoming the shelter that marine organisms use for protection (phytoplankton, sea shells, coral reefs, etc). As the diagram illustrates these reactions are in equilibrium. The Carbon cycle in out oceans is very similar to the carbon transport system in our blood , EXCEPT we do not make an insoluble precipitate, CaCO3 (s).
In our bodies we must get rid of the carbon dioxide that is released as a by – product of cellular respiration.  We dissolve the CO2 (g) in our plasma (water part of out blood) and because of fact that CO2 (g) is Lewis acid it lowers our blood pH which will force us to breath.

Not only does equilibrium system help transport CO2 (g) out of the body through the plasma it also serves an important blood buffer that keeps you blood at a pH of about 7.4.

Mechanism of how Carbonic acid  can be decomposed back into water!

Standardization of the Strong base in this back titration of TUMS.
In this analysis of the “active ingredient” of Tums ( CaCO3 ) we will need to use a strong base to titrate the excess HCl that was used to drive the reaction to completion:

Net Ion:          2H+ (aq)   +   CaCO3 (s)   —>   CO2 (g)    +     H2O (l)   +   Ca+2
Excess
The excess Strong Acid will drive the reaction to completion due to Le Chateliers Principle.  It also important to to have excess Strong Acid to react with all the CaCOthat will be mixed and “hidden” with the binder, coloring, flavor, and etc.  That is why it is important to crush the tablets (tabs!) with a mortar and pestle in order to expose all of the salt, CaCOto the acid.

Now after we add the excess acid we will have to Titrate this excess acid with a Strong Base. This lab produces incredibly accurate results ONLY IF OUR SOLUTIONS that we use ARE ACCURATE.  We are adding 0.04 moles of protons from the 100.0 ml of a 0.4 M HCl solution.  Because we are adding about 0.01 moles of extra protons from the strong acid we need to titrate the excess protons with a strong base AND that solution needs to verified or STANDARDIZED.

I made a 0.5 M NaOH solution. I was very careful to make this solution BUT because strong Bases are very reactive that solution is definitely LOWER in concentration as the hydroxide reacts with the CO (Lewis Acid) in the air.  I used 20 grams of solid NaOH (.5 mole) dissolved in a 1 liter of solution to make a 0.50 M NaOH solution
BUT not all of the solid is NaOH as CO2  from the air will cause the NaOH to become Na2CO3. This also happens in solution.  Strong bases are carbon dioxide scrubbers that are used to remove it from space capsules.

2NaOH(s)    +     CO(g)     —–>  Na2CO     +     H2O

Also NaOH is deliquescent which means it can absorb water from the air and start dissolving itself. This would add weight to the Base and dilute is quantity.

Because NaOH has these issues we need to verified or STANDARDIZE it with a weak acid that is not reactive and does not have these issues. A perfect solution to this (no pun intended!) is using KHP. Potassium Hydrogen Phalate.

KHP, (KHC8H4O4) is excellent to standardize a Strong Base with because it

1. Weak Acid – thus does not react unless forced to by a Strong Base
2.  Is a solid –  we eliminate volume errors when making this solution
3.  It has a large molecular mass (204 g/mol) – measurement errors with a large
to large mole errors.

Net Ion:  HC8H4O4–     +     OH–      —->    C8H4O4– 2       +       H2O

You will find from this standardization that my solution of 0.50 M NaOH is less but we need to know its exact value to proceed with the lab.

Today’s Tums Lesson:

______________________

12/3 – Friday Homework: –

1.  Please Complete the worksheet below and review with the key.

Analytical Acid Base.pdf
Analytical Acid Base key p.pdf

2.  Begin your write-up of Lab 13:  I have emailed you a link to a shared doc to start the following.

You only need to complete what is in BLUE.

a) Background –  A full page single typed.  There is so much to write about. Do not forget to direct your discussion toward                the Objective (which is to determine the milligrams of calcium carbonate in TUMS).

b) Objective – What is purpose of this lab?
c) Detailed written procedure There are 3 parts to your procedure.
( I will be scrutinizing your procedure and the conclusion)

The procedure has 3 parts!:
1) Design of the lab. Started this today. Please watch the lecture posted above to complete this part                        of the procedure in your shared doc. THIS ALONG WITH YOUR BACKGROUND and OBJECTIVE is DUE                        MONDAY. YOU NEED TO WATCH THE ENTIRE VIDO TILL THE END to understand the
Standardization part.

2) Preparation of chemicals necessary to perform Back – Titration  on 2 tabs of
750 mg TUMS (calcium carbonate = active ingredient)

3) Actual Steps taken to perform the lab in order to calculate the mg of active ingredient in 2 tabs of TUMs.

a) Standardization

c) calculationsNeatly presented – I  have a video below that reviews how to complete the
calculations below.

So far you only have the calculations for the standardization and the calculations for the making of the solutions needed in your design.

d) data table (typed) – not yet

DESIGN YOUR DATA TABLE, BASED ON YOUR STEPS in the procedure that describes what you need to do to completely determine the milligrams of calcium carbonate in your TUMS tablet.
This will help you understand the Lab better and give you a head start to what we will do Monday when we Titrate the TUMs.
End of week 3!