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## Q2: Week 1  – 11/15 – 11/19

11/15 – Monday – A Day – 2/3a Lab, 4

Main focus –

a) To Review Lab conclusions.

b) To review the concepts of Test 2 that tie into Acid/Base.

c) To View a pH Titration curve and determine the unknown concentration,                                equivalence point, half equivalence point, and the final concentration of the titrant.

Period 2/3:

1. Hand back Labs for review of conclusion writing.

2.  Review of Test 2.

3.  Pre- titration worksheet review and provide the Lab set-up that represents each                       problem.  The idea is to connect these stoichiometry problems to the lab procedure.

Acid Bases Pre-Titration key p.pdf

4.  Continue to mark up the The Strong Acid and Base Titration pH curve to verify the:

a)  Initial pH of the solution

b)  half equivalence Point ——–> initial concentration (M) of analyte (acid in this case)

c)  Equivalence point —-> pH at equivalence.

d)  end point

e)  final pH of the solution

Period 4:

1. Complete #3 from above.

Lab 10 Preview – Strong Acid/Base Titration:

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11/15 – Monday Homework: –

1.  Please view titration below (virtual Lab 11 Preview) THAT IS NOT A STRONG ACID STRONG BASE Titration.
Analyte: Weak acid: HC2H3O2  – Acetic acid  25.0 ml of unknown concentration                       Titrant: Strong Base : NaOH = 0.12 M

2.  From the Titration curve of this Volumetric Titration please complete the following on the Graph:

Weak Acid (Acetic Acid – 25ml) Strong Base (NaOH = 0.12M).pdf

a: Determine the concentration of the acid.
b: Determine the equivalence point of the titration. (Identify of the graph)
c: Determine the end point of the titration using the indicator. (Identify on the graph)
d: Determine the halfway equivalence point. (Identify on the graph)
e: Confirm the final pH of the titration.
f: Confirm the initial pH of the titration. (skip this)
g: On the four points of the titration curve, (initial pH, final pH, equivalence point, halfway equiv.)
determine the percentage of the Acid/Base (skip this)
h: Write the net-ion reaction.

1: Lab 11 Preview – Weak Acid/Strong Base Titration:

25.0 ml of an unknown concentration of Acetic Acid is titrated with 0.12M NaOH.                                                               3 drops of Phenolphthalein was added before the titration began.

End of Monday..

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11/16 – Tuesday – B Day – 2, 3b/4 Lab

Main focus –

a) To identify the equivalence and half equivalence points on a pH titration curve.

b) To estimate the equivalence pH and half equivalence pH along with calculating the             final pH of the titration.

c) To calculate the initial concentration of the analyte.

Period 2:

1.  Strong Acid / Strong Base Titration – Perform the titration and print out the graphs

Period 3/4:

1. Hand back Labs for review of conclusion writing.

2.  Review of Test 2. ( I did not get to do this today. I will find time another day)

3.  Pre- titration worksheet review and provide the Lab set-up that represents each                       problem.  The idea is to connect these stoichiometry problems to the lab procedure.

Acid Bases Pre-Titration key p.pdf
4. Lab 10 : Strong Acid / Strong Base Titration                                                                                                                                                                                                                                                                                 5. Lab 11: Weak Acid / Strong Base Titration

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Lab 10 – Strong Acid / Strong Base Titration

In this Lab we were trying to determine the concentration of a the strong acid solution using a KNOWN concentration of a STRONG Base.

Thus 25.0 ml of Strong Acid (HCl) in the small beaker was titrated with 0.5 M Strong Base, NaOH

1: Determine the concentration of the acid.
2: Determine the equivalence point of the titration. (Identify of the graph)
3: Determine the end point of the titration. (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.
7: On the four points of the titration curve, (initial pH, final pH, equivalence point, halfway                                equiv.) determine the percentage of the Acid/Base
8: Write the net-ion reaction.

Lab 10 Review of Strong Acid/Strong Base Titration:

This review the virtual lab titration. I review all the steps and requirements for this. I am using the graph generated by the Strong Acid / Strong Base Titration in the virtual Lab below this review video.  What I go over is in this video is the same concepts but different data from what you did in Lab today.

I am using the following titration graph that was part of Friday’s Homework:

Strong Base(0.12M) Strong Acid (25.0 ml) Titration.pdf

End of Monday..

Lab 10 Virtual Lab used in Review video above- Strong Acid/Base Titration:

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11/16 – Tuesday Homework: –

1.  Please complete Lab 10 using the Lab 10 Review video that reviews all the steps to your lab. Please write on your lab and number each objective . The requirements are posted above.  WE HAVE DONE THIS ONCE BEFORE (FRIDAY”s HOMEWORK!)

2. Complete the Lab Titration problem/Form:
You are going to complete the Form below BASED ON the Titration GRAPH  below in which
25.0 ml of unknown concentration of HCl is titrated with 0.03 M of Ca(OH)2.
Please use the graph below to complete in the same way that you completed lab 10.
Strong Acid Base Titration Form worksheet.pdf
On the Printed graph or on a separate piece of paper please number your work! Careful with the stoichiometry!

1: Determine the equivalence point of the titration. (Identify of the graph)
2: Determine the concentration of the acid.
3: Determine the end point of the titration. (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.
7: On the four points of the titration curve, (initial pH, final pH, equivalence point, halfway                                equiv.) determine the percentage of the Acid/Base
8: Write the net-ion reaction.
3.  Complete the Form using your values from the Strong Acid Base Titration Form worksheet.pdf

3: Strong Acid Strong Base Lab Form:

End of Tuesday..

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11/17 – Wednesday – A Day – 2/3a Lab, 4

Main focus –

a) To Review the concepts of a strong acid strong base titration.

I am absent today.  I will provide a link to a zoom meeting to review the lab and the form.  Sorry for the confusion for question 7 and 8. Stay tuned.

Mr. Grodski is inviting you to a scheduled Zoom meeting.

Topic: AP Chemistry 11.17
Time: Nov 17, 2021 08:15 AM Eastern Time (US and Canada)

Meeting ID: 829 9410 6657
Passcode: Ht2ZBP
One tap mobile
+16465588656,,82994106657#,,,,*679927# US (New York)

Period 2/3:

1: I will review the Lab and the form last night by using the Forms Titration Curve which is based on

25.0 ml of unknown concentration of HCl is titrated with 0.03 M of Ca(OH)2.
Strong Acid Base Titration Form worksheet.pdf

2. Lets review Monday’s weak acid Strong Base titration homework.

Weak Acid (Acetic Acid – 25ml) Strong Base (NaOH = 0.12M).pdf

What is similar and dissimilar with the STRONG ACID STRONG BASE (LAB 10)  titration?
a) Starting pH   b) Ending pH   c)  size of the asymptote?  d) pH at equivalence e) Buffer region

What is new with this titration? – Notes below!
a) How to determine the Ka from the half equivalence point
b) Describing the pH at the equivalence point – Why is not at 7?  We will calculate this in the spring.
c) Henderson Hasselbalch Derivation – Maybe

Period 4: –

Same as above.

Side by side comparison of the two type of titrations:

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11/17 – Wednesday Homework: –

1.  There is no homework tonight unless you want make another submission to last nights form.
Lab 10 is due tomorrow – everything is done on the graph.
Make sure you number the objectives on the graph.

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11/18 – Thursday – B Day – 2, 3b/4 Lab

Main focus –

a) To perform a weak acid / weak base titration.                                                                                   b) To identify the equivalence pH to be above 7.                                                                                     c) To identify the effects of the active conjugate base in this type of titration.

What is new with this titration? – Notes below!
a) How to determine the Ka from the half equivalence point
b) Describing the pH at the equivalence point – Why is not at 7?  We will calculate this in the spring.
c) Henderson Hasselbalch Derivation – Maybe

Period 2:

1.  Weak Acid / Strong Base Titration – Perform the titration and print out the graphs
2. Start working on the objectives listed below

Period 3/4:

1.  Weak Acid / Strong Base Titration – Perform the titration and print out the graphs
2. Start working on the objectives listed below
3. l reviewed the percentages of conjugate base /acid through points 1 – 4 and explained why the pH at equivalence was above 7.

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Lab 1 1 – Weak Acid / Strong Base Titration

In this Lab we were trying to determine the concentration of a the weak acid solution using a KNOWN concentration of a STRONG Base.

Thus 25.0 ml of Weak Acid ( HC2H3O2 )  in the small beaker was titrated with 0.5 M Strong Base, NaOH

1: Determine the equivalence point of the titration. (Identify of the graph)
2: Determine the concentration of the acid.
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)
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.

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11/18  – Thursday Homework: –

1.  Please complete objectives 1 – 5, 7 & 8 ONLY of Lab 11 using the Lab 11 Review video that reviews all the steps to your lab. Please write on your lab and number each objective . The requirements are posted above.

SKIP objective number 9 and 6!

Lab 11 Preview – Weak Acid/Base Titration:

End Of Thursday!

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11/19 – Friday – A Day – 2/3a Lab, 4

Main focus –

a) To derive the Henderson – Hasselbach Equation

b) To identify the buffer region in a titration curve

c) To Calculate the Ka of a weak acid through a titration curve and approximate Point 3.

d) To introduce the concept of pKa and how it is used with Acid/base Indicators.

Period 2/3:  –

1.  We will use the Lab 11 to identify the buffer region of the Titration curve and Derive the Henderson – Hasselbach                    equation.

2.   We will use Lab 11 to determine and calculate the Ka of the weak acid in the titration (acetic acid).

3.   Approximate point three of the titration curve.

4.   Compare and contrast both titrations in Lab 11 and 12 and collect both labs.

Period 4: –

1.   Same as above

2.   Collect both Lab 10 and Lab 11.

Today’s Notes:

The new skills that we learned from Titrations in Lab 10 and 11 are identifying the parts of a Titration curve.  The striking part of the Titration graph is the asymptotic line that occurs as the pH changes becomes exponential changes as the pH nears the equivalence point.

We learned the endpoint in an Acid/Base titration is really an approximation of the equivalence point.  The endpoint refers to the volume of titrant added (Standard Base Yesterday) and pH that results when the chemical indicator changes color.  This color change will never be exactly at the equivalence point but it approximates the volume of titrant added if the indicator has a color change on the asymptotic line near the equivalence point.

Consider our last 2 titrations.  We used phenolphthalein which has a color change (turns from colorless to pink at pH changes of 8 – 9).  What if we used Thymol blue or Methy red?

 Table M Do not forget that these indicators are themselves conjugate acid base pairs in equilibrium. In the case of Thymol blue

Notice in the first Titration which you should recognize as a strong acid / strong base titration, with a pH of the equivalence pH of 7, can utilize both Thymol blue and Methyl red as indicators as the endpoints will be on the asymptotic line.  They would have endpoints with approximately the same volume as the equivalence point.

In the second titration you should recognize as as weak acid / strong base titration because the starting pH is greater and the equivalence point pH is NOT 7!  In this titration the asymptotic line is not quite as long thus Methy Red would no longer be appropriate to use because its color change would occur at MUCH different volume than the equivalence point volume resulting in a very poor approximation of the volume needed by the titrant to neutralize the acid.  It would lead to undervalued concentration of the acid in this case.  THymol blue however would however lead to very good approximation of the equivalence volume because its color change is closer to the equivalance point.

Notice both the Titrations have an equivalence volume of 50 ml of base added, illustrating that both acids are at the same concentration even though the acid in the titration on the right is a weaker acid.  The Strong Base DRIVES the weak acid to COMPLETION like the Strong Acid on the Left does naturally.

Remember the Volume at the equivalence point is what is normally needed to attain the concentration of the solution being titrated  (acid in both cases above and in our lab 10 and 11). This volume of added titrant (chemical with known concentration) is used to determine the concentration of the solution in the beaker under the buret.

The new skill that we added in our graphical analysis of acid base titrations allows us to determine the Ka of acid, or conjugate acid (produced from a base that is titrated).

Remember Ka is really a Keq which is a equilibrium constant that expresses whether the products or reactants are favored.  I have been surprised how many students have asked what this in the past few days?  We have discussed that Keq in terms of thermodynamics when we talked about spontaneity which if you remember is pathway that the universe supports.  A favorable pathway always is supported by a dispersion of energy from a concentrated source (increase in entropy).

Reactants   —–>   Products
Since Keq generally = [Products] / [Reactants]

Then a Keq greater than  1 is a reaction that has more Products than Reactants at equilibrium.
If there are more products present at equilibrium then THE FORWARD DIRECTION is more favorable pathway then the reverse reaction (which would build up reactants if more favorable).

The forward reaction then is more spontaneous!

Strong Acids have an incredibly large Keq because virtually all of the acid dissociates to leave virtually zero reactants which would drive the Keq to a VERY LARGE NUMBER! Strong Acids dissociate very spontaneously!

HCl  –>  H+   +    Cl

Keq  = [H+][Cl] /  [HCl]

Keq = VERY LARGE

Weak acids have an incredibly small Keq because virtually all of the acid remains undissociated and thus there are less products and more reactants. Weak acids dissociate very UNspontaneously!

HC2H3O2  —–>  H+   +   C2H3O2

Keq   =    [H+][C2H3O2] / HC2H3O2

Keq  =   Very Small

Now because these reactions are very similar  (HA   —->  H+  +   A– we call them Ka!
Keq  = Ka when we deal with acids dissociating.

We can find the Ka graphically because of the relationship between Ka and what it equals:

Using this relationship we know that when we have equal amounts of conjugate Base (A) and conjugate acid (HA) the log [A] / [HA] will go to zero because the log of 1 = 0 !!

Thus when [A]  =  [HA]   pH = pKa

and we can get the pKa of acid which is just the -log of the Ka.  Once we have the pKa we just

perform the 10-x calculation to attain the Ka  of the acid.

How do we find the point where the conjugate Base (A) and conjugate acid (HA) are equal

We find the half equivalence point!!! (point 2!)

 So once we establish the equivalence point which is in the middle of the asymptote we attain the volume at that point which in the example to the left is 20 ml.  Now we take the equivalence volume and halve it:                                        20 ml / 2 = 10 ml 10 ml represents the volume of titrant (base) added to neutralize half of the acid.  This point is where half of the weak acid has been converted to the conjugate base.  So if we had 1 mole of weak acid, .5 moles of the weak acid remains and  .5 moles of conjugate base has been created. This is the point where the acid = conjugate base !                              pH of this point = pKA
So in the above example the pH at the Half – equivalence point is equal to 3.  Pka of the acid = 3.

The Ka of the acid is thus:    10-3 =    1 x 10-3

This is a Ka of a weak acid because it is less than 1 which means the reactants or the undissociated acid ( HA ) is a larger quantity because the reverse reaction is more spontaneous.
Instead of pH ranges for the color changes for chemical indicators we can use pKa’s
They are also acid/base equilibrium systems

HIn    <—>   H+    +     In

and thus they also have Ka’s and pKa’s

What do you think the pKa can tell us about the acid/base indicators?

What is significant about the pKa of the acid base indicators in terms of of the pH ranges?

Henderson – Hasselbach Equation intro!!!!:

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11/19 – Friday Homework: –  Make sure you refresh this page to make sure you have the current version!!!!

1. Complete the worksheet below and review with the key. You can also you the video below to review the worksheet with me. The key here is to identify what point on the titration graph (1 – 5) the acid base questions is asking about,
The video below teaches the concepts covered in Fridays lesson.
Acid Base Lab Titration Graph Questions.pdf

Titration Graph Lab questions Key p .pdf
2.  Please complete the Weak Acid Strong Base Form posted below using the given  Titration graph:
You are going to complete the same work that you did with Lab 11 on a new titration graph that is also a Strong Acid Strong Base Titration.  The titration uses the following:
25.0 ml of unknown concentration of  HC2H3Ois titrated with 0.03 M of Ca(OH)2.
Please use the graph below to complete in the same way that you completed lab 10.
Weak acid Strong Base Titration Form worksheet.pdf
On the Printed graph please number your work! You are putting these values into the form below AND ARE HANDING THE GRAPH WITH YOUR WORK ON IT FOR A QUIZ GRADE MONDAY.
Meghan just send me a pic of your graph.

1: Determine the equivalence point of the titration. (Identify of the graph)
2: Determine the concentration of the acid.
3: Determine the end point of the titration if bromthymol blue 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)
7: On the four points of the titration curve, (initial pH, final pH, equivalence point, halfway equiv.)
determine the percentage of the Conjugate Acid/ Conjugate Base / OH
8: Write the net-ion reaction.
9: Determine the Ka of the Acid.

New Skills
pKa = pH at half equivalence point
a) determining Ka of Acid Graphically
b) determining indicator based on pKa
c) Henderson – Hasselblach equation derivation

1. Acid Base Lab Titration Graph Questions:

2: Strong Acid Strong Base Lab Form:

End of Week 1!