Select Page

  Q2 : Week 1  – 11/14 – 11/18

<- Week 10(Q1) –  Week 2 ->                                                                                                                          Jump to:  Tuesday,   Wednesday,  Thursday,   Friday 

Refresh this page every time you arrive!  I update this daily!!!

If you have not already please join the REMIND for this class. 

Please Make sure Your 1st Quarter Grade Is accurate !  After Thursday these grades will not change.                               

LAB 7 – Empirical Formula of copper Iodide is due  !

Labs 1,2,3,4,5,6,8,9 are Late!  

<Week 11(Q1)   –   Week 2>                                                                                                                          Jump toTuesday,   Wednesday,  Thursday,   Friday 

Refresh this page every time you arrive!

If you have not already please join the REMIND for this class. 

Please Make sure Your 1st Quarter Grade Is accurate After Thursday these grades will not change.                               

_______________________________________________________________________________________________________________________________________
 11/14 – Monday – B Day – 2, 3b/4 Lab                                       Jump toMonday Homework

 Main focus –                                                                                                                                                         
                                                    

a) To Take Acid/Base RAT 1

b) 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: 

1.  Test 3 (1st quarter) –  1st try.

a) Individual component – 50%

b) Group Component – 50%

Period 3/4: 

1.  Test 3 (1st quarter) –  1st try.

a) Individual component – 50%

b) Group Component – 50%

2. 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 Base Pre- Titration . pdf
View Download
 
Acid Bases Pre-Titration key p.pdf
View Download
 
                                                                           

                                                                                                                    

 _____________________________________________________

11/14 – Monday’s Homework: – 

1.  Please review the Today’s (or yesterday’s)  RAT .  Expect a new Rat Friday that will include the same information but includes acid/base stoichiometry and net ion equations, which your weekends homework was based on!
                                                                                                                                                                                             It will count as a TEST 3 in quarter 1!!! I will take the better of the 2 RATS as Test 3!!!
 
Tuesday‘s RAT will be the same PLUS I will add i question with a net ion reactions and 2 questions with acid /base stoichiometry.  Please review the weekends’ homework worksheet which reviews both concepts. 
 
Stoichiometry 5a – Acid Base Reactions new Key.pdf
View Download  
                                                                                                                                                                                 Here is the blank RAT from today:      
Acid Base skills RAT 10 questions E009.pdf
                                                                                                                                                                                        Rat #1 – Acid Base Intro Basic Review: You probably do not need too much of this as you reviewed in class  
when you took the group portion of the quiz. I will have a video posted below that reviews every question of the the RAT. You will see similar questions tomorrow.

 

2.  I made a new worksheet and Video that could help with writing Net Ion Reactions for Acid Base Reactions. Please print and follow along with me.

Writing Net Ion Acid Base Reactions.pdf

 

Review of the First Acid / Base RAT

This video has timecode buttons under the description to move to the question you need to review.
You will have to play in Youtube to see the descriptions!                                                                                                                                           

 

Writing Net Ion Acid/Base reactions Review –

                                                                                                                                           


End of Monday..

_______________________________________________________________                                                         Jump toTuesday Homework

11/15 – Tuesday – A Day – 2, 3a Lab/4                                                                       

Main focus –                                                                                                                                                         

                                                   

a) To take the Second Acid / Base RAT

b) To Complete the Pre-Titration worksheet – Acid/Base Stoichiometry  

 

Period 2/3a –  

1. Tie Net Ion acid base writing with determining acid/base/neutral salt determination with notes below.

2. 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 Base Pre- Titration . pdf
View Download
 
Acid Bases Pre-Titration key p.pdf
View Download

2.  Test 3 (1st quarter) –  2nd try.

          a) Individual component – 50%

          b) Group Component – 50%                                                   

Period 4 –

1.  Test 3 (1st quarter) –  2nd try.

          a) Individual component – 50%

          b) Group Component – 50%

 

                                                             

_________________________________________________

ACID and Base NOTES – Acidic, Basic, or Neutral salts

Notes for acid/ base salts:

Ionic compounds will dissociate into their cations (+) and anions (-) IF THEY ARE SOLUBLE and when they do they can act as either a base or an acid (or not react at all) in water.  If the ions of the salt act as an acid or base they can ionize water as either a hydronium ion (H3O+) or as a hydroxide ion (OH) by following our acid/base definitions.  How do we know if a salt is an acidic, basic, or neutral salt?

We first must identify the ions from a soluble salt THAT ALWAYS SPECTATE! These are the ions that result from strong acids and bases.

IF ions of a soluble salt are made entirely of the ions of a strong base or strong acid they will make a neutral salt as these ions cannot ionize water.

For example if we have the following soluble salt:  KCl

                                                                     

                                                                     KCl    —->     K+   +     Cl

Niether  K+   +     Cl–  can ionize water meaning they have no ability to act as base and pull a proton off water to make a hydroxide ion nor can they force a proton on a water creating the hydronium ion.  This salt and every salt made of the ions of strong acids and bases cannot change the pH and thus are NEUTRAL SALTS.

Ions that have the ability to ionize water means that these ions from a soluble salt can FORCE water to act as an acid or base.  Water is a very weak acid and a very weak base.  It can act as either but it is driven to act as a base if it is paired with a stronger acid while it will be driven to act as a acid if it is paired with a stronger acid. This means that these ions have acidic or basic properties because they are NOT spectators from a strong acid or a strong base. They must be active conjugate bases or acids!

For example if we have the following soluble salt:  NH4Cl 

                                                                    NH4Cl    —->     NH4+   +     Cl

NH4+WILL IONIZE Water :

                                                       NH4+  +   H2O    —->    H3O+ +   NH3

Since we are increasing the hydronium ion the pH drops and ammonium chloride is an acidic salt.

For example if we have the following soluble salt:  Na2CO3

                                                               Na2CO3     —->   2Na  +   CO3-2

CO3-2 will IONIZE water:

                                                      CO3-2  +   H2O    —-> HCO3-1   +   OH

Since we are increasing the hydroxide ion the pH increases and sodium carbonate is Basic salt!

What about these expensive pool chemicals????

Here are some expensive pool chemicals that change the pH.
If the pH is not optimum (about 7.4) then the disinfectant (chlorine) will not work and the liner, metals (on heater), or grout (in stone pools) will decompose.
                             Na2CO3                                                                                                NaHSO3
                                           Washing soda                                                                                             Toilet bowl cleaner/fungicide

 

                          Basic Salt                                                                          Acidic Salt

_____________________________________________________

11/15 – Tuesday’s Homework: – 

1Please review your acid/base concepts that may help answer your last 2 questions. The second part of the homework would be helpful. Also last weekends homework (stoichiometry 5a worksheet video and key). 

2.  Please complete the Pre -Titration worksheet and review with the key.  We started this in class. Remember that in an Acid/Base titration you need to match every OH- with a H+ and this is called neutralization.  WE also call it reaching the  ” equivalence point” (with pH probes) and the “end point” if we use acid/base indicators. 

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

 
3 Please watch the lecture on Acid/ Base pH Titration Intro lesson:                                                                                                                 
4 Then Read the notes posted below:                                                                                                                                                                                                                                                                                                                    5.  View the Strong Acid / Strong Base Virtual Lab below and use the following graph of this titration to                    complete the following:              
       
        a) Write the Net Ionic Reaction
        b) Calculate the Molarity of the acid that is being titrated    
                                                                                                                                                                    Strong Base(0.12M) Strong Acid (25.0 ml) Titration.pdf  
View Download

   

                               

_________________________________________________

ACID and Base NOTES – Acidic/Base Titration Notes 

The new skills  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 ) 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.
 
Consider the titration in the lecture (Strong Acid/Strong Base).  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. The titration on the right is a Strong Base/weak acid concentration that we will study and do in lab next week. NOTICE THE ENDPOINT IS NOT AT A pH of 7 in this case!

3. Acid /Base pH Titration Intro lesson:

 

5. Lab 10 Preview – Strong Acid/Base Titration: Watch the lecture above to understand this!

We will be performing these Acid/Base Volumetric Titrations in class soon but the basic reason we do them is to analyze or determine the concentration (Molarity) of the chemical in the beaker (analyte) by adding enough of a known solution of Base (titrant) in this case to exactly neutralize the acid.

The plot of the pH (from the pH probe in the solution of the acid) vs the volume of Base added is completed by the computer in real time.  How the pH changes with volume of base added will help us determine the original Molarity of the acid. 

 The final pH Curve from the video:                                                                                                          Strong Base(0.12M) Strong Acid (25.0 ml) Titration.pdf  
View Download

 

  _________________________________________________________________________                                  Jump toWednesday Homework

11/16 – Wednesday – B Day – 2, 3b Lab/4

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 –                

1Complete RAT 2 – 

       – 5 minutes to complete the 2 two questions you were given an opportunity to complete.

       – 20 minutes to complete ticket in groups

2.  Review of Homework- Determining the concentration of the acid 

3.  Strong Acid/Strong Base Titration Lab 10 –   

        – complete the titration and print out graphs.    

Period 3b, 4 –        

1. Complete RAT 2 – 

       – 5 minutes to complete the 2 two questions you were given an opportunity to complete.

       – 20 minutes to complete ticket in groups

2.  Strong Acid/Strong Base Titration Lab 10 –  

          – complete the titration and print out graphs.

 

 
                                                                                                                       

______________________

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 0.06 M Strong Base, Ca(OH)2 

     

On the Printed graph please number your work!
 
    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 Tuesday’s Homework.  If Tuesday nights homework did not make sense then I am really doing it for you in the video below. Use the video to help complete the lab.

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

 

______________________________________________

11/16 – Wednesday Homework: –

1.  Please complete Lab 10 using the Lab 10 Review video posted above that reviews all the steps to your lab. Please write on your lab and number each objective. All of this can be written on the printed graph of the actual titration that you did today.

The requirements are posted above in Lab 10 description.

Here are the pdfs of the computers for lab 10 from period 2:

Table 2

Table 3

Table 4

Table 5

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
View Download
                                                                                                                                                                                                           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 Wednesday…

 

 

                                                                                                                                                                                                                            Jump toThursday Homework
__________________________________________________________________________________________________________________________________

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

Main focus –     
                                                                                                                                               

a) To calculate the molarity of an analyte (acid) by acid/base volumetric titration.

b) To complete a weak acid / strong base titration.

c) To observe the differences between the two types of titrations.

d) To identify the equivalence pH to be above 7.                                                                         

e) To identify the effects of the active conjugate base in this type of titration.     

 

                                                                                                                                                         

Period 2/3a – 

1. Review Tuesday/Wednesday nights homework.

    a) Asymptote of titration curves, general shapes

    b) Review the concepts of the equivalence point vs. the endpoint.

 Form 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
View Download

2.  Lab 10 – Review

3.  Lab 11 – Weak Acid Strong Base Titration – 

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 – 

1.  Lab 10 – Review – 

2.  Lab 11 – Weak Acid / Strong Base Titration

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

                                                                                                 

______________________

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 0.06 M Strong Base, Ca(OH)2 

     

On the Printed graph please number your work!
 
    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 – Strong Acid/Base Titration: 

This video is a Strong Acid/ Strong Base Titration using a 0.12 M NaOH as the titrant and 25.0 ml of an unknown HCl concentration (analyte).  This is not the same as the actual lab but the graph is universal to all Strong Acid Base Titrations.

The final pH Curve from the video:                                                                                                          Strong Base(0.12M) Strong Acid (25.0 ml) Titration.pdf  
View Download

 

 ______________________

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 0.06 M Strong Base, Ca(OH)2 

     

On the Printed graph please number your work!
 
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.


 

                                                                Side by side comparison of the two type of titrations:

                           Strong Acid/ Strong Base play at 1.75 speed 

                      Weak Acid/ Strong Base play at .75 speed

 

 

                                                            What are the observable differences between the two types of titrations?

                                                                                                                                                                                                                                     

 

 

______________________

11/18 – Thursday Homework: – 

*LAB 10 Due in Crate Friday based on the requirements listed above.

WE are not working on Lab 11 tonight BUT are using new concepts to practice.

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 AND the video below, please complete the following on the Graph using the video below:  I may collect this.

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

                                                                                                                                                                                      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.                                                                                                                                                                                   _______________________________________                    

OR In lab 10 we did a Strong Acid / Strong Base Titration and it is not the norm. In fact its almost never done in analytical acid base chemistry because most acids and bases are weak thus when we want to analyze a chemical that has acidic or basic properties it most often a weak acid or weak base.

Our Lab 11 titration is what is actually done in largest quantity where a weak acid (in this case) is analyzed with a Strong Base.  Weak acids have like acetic acid (vinegar) in this lab dissociate only about 5% Thus a strong base is needed to DRIVE the reaction to completion. That is we make the weak acid ACT like a strong acid by having a strong base RIP every available H+ away from it.  That way we can use stoichiometry (ratios) to solve for the concentration of the acid,

1.  Please complete the Lab 11 on the Graph like we did with the Strong Acid Strong Base Titration.

2.  Please view the Lab 11 Review Video to complete the Lab.  There will be 5 points to identify in titrations that that are NOT STRONG ACID / BASE titrations in and they include:

1. Initial pH

2. Half equivalence

3. Buffer Position – Explained In video below

4. Equivalence Point

5. Final pH

Also there is a new skill in determining the Ka of the weak acid and that will also be covered in the video below OR the note after the video.

Please follow the lab requirements ON THE GRAPH posted above for Lab 11.

________________________________________________________________________________________________

 

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.

 

Lab 11 Review – Weak Acid/Base Titration:

 End Of Thursday!

_________________________________________________________________________________________________________________________

11/19 – Friday – B Day – 2, 3b 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.

Every Titration Curve Has 5 points that need to identified or calculated AND every ACID/BASE problem represents every one of these points. They include:

Point 1 = initial pH 
Point 2 = half equivalence – obtain Ka of acid through Henderson-Hasselbach equation
Point 3 = buffer position (when any ml of titrant has been added but is less than equivalence)
Point 4 = equivalence point
Point 5 = final pH.   

We will focus on Point 2 and point 3 today. These points occur in weak acid/strong base and strong acid / weak base titrations as there are no buffers in strong acid / strong base titrations.

Period 2 – Solve for the concentration of the acid and then compare both titrations!!

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.

5.   Chemical Indicators and their pKa’s!!!!

Period 3b/4 – Solve for the concentration of the acid and then compare both titrations!!

1.   Same as above

2.   Collect both Lab 10 and Lab 11.   

3.  Lab activity – Not a Lab – Practice skills learned

      a) Determine the concentration of the weak acid with a Standard Base using a chemical indicator.

      b) Determine the Ka of the acid.

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]   the 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!!!!:

_______________________

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
View Download
                                                                                                                                                                                                                                    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
View Download
                                                                                                                                                                                                                                     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!