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     Q2 : Week 3 – 11/27 – 12/1

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– Regarding Homework assignments – IF you cannot complete the assigned homework before school the next day you must email me.

LAB 10, and 11 are DUE!!! 

   ________________________________________________________________________                                    Jump toMonday Homework
 11/27 – Monday – B Day – 2, 3b/4 Lab                                         

 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, Collect Lab 11.

1 – 5.   Same as above.

6.  Review of every point in titration of Lab.  Modeled each step. Began point 3!

 

                                                                                                                    

 

                                                                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?

                                                                                                                                                                                                                                     

 

_________________________________________________

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!

 
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?

 

Acid Base Indicators Presentation:

Henderson – Hasselbach Equation intro!!!!:

_________________________________________________                                                                       jump to:  top                               11/27 – Monday Homework: 

1. Complete Lab 11 using the Weak Acid Strong Base Titration review Video and the lab requirement posted below:
 
Period 2 watch this entire video and complete your lab. 
Period 4 watch 10:00-27:00.

                                                                                                                                                                                        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 WEAK 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 11.                                                                    
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 TUESDAY. 
 
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: Weak Acid Strong Base Titration Graph Questions:

 

 ______________________

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.


 2. Weak Acid Strong Base Lab Form:

 

_________________________________________________________________________                    Jump toTuesday Homework /top           11/28 – Tuesday – A Day – 2/3a Lab, 4                                            

Main focus –                                                                                                                                                         

a) To review the weak acid /strong base Titration

b) To identify buffer solutions

c) To use the Henderson – Hasselbach to answer point 3 questions

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.   

 

Period 2/3a: 

1.  Download this Titration file and use the printed graph to mark up.

WEAK/STRONG Acid, Strong Base Demo.gambl
View Download

– Used this file that was an overlay of the 2 type of Titrations we have done

– reviewed the five points to review buffer region and derived Henderson – Hasselbach equation, predicting pKa and Ka.

– Reviewed pH, pOh, Kw, water basics

Point 3 problem review!  Breaking down the pH buffered in front or after the half equivalence point.

Period 4: 

1. Same as above working with Titration File

Point 3 problem review!  Breaking down the pH buffered in front or after the half equivalence point.

_____________________________________________________                                                                                      jump to:  top                        11/28 – Tuesday’s Homework: – 

 
1.  Complete Lab 11 using the requirements posted in Monday’s post.  You should have all the skills to do so after today.  Please use the video posted on Monday that reviews how to do this with a similar titration. Remember it has its separate curve from the lab. If you are stuck please provide me with questions tomorrow.
 
 
2.  Everyone has 2 more submissions on Monday nights form if you did not get the trophy.  It was a form on another Weak Acid/Strong base Titration titration graph (that was given in class). It uses the same skills needed to complete the lab.
 
Weak acid Strong Base Titration Form worksheet.pdf
View Download
 
3. 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 today’s lesson. The Only Difference here is that in this case we are adding a Strong Acid to a Weak Base. Different problem using the same concepts!!
 Please read the Acid Base Indicator notes below for question 1 c  – Use the  Determining Ka, Indicator worksheet review video posted in Wednesday to review pKa’s with indicators next year.                              
                                                                                      
Acid Base Lab Titration Graph Questions.pdf
 
 Updated!
Acid Base Lab Titration Graph Questions Key NEW .pdf
View Download

 

Please read the Acid Base Indicator notes below for question 1 c
 
Acid Base Indicators Notes for question 1c
 
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?
 

1. Acid Base Lab Titration Graph Questions:

 

_______________________________________________________________________________            Jump toWednesday Homework /top 
11/29 – Wednesday – B Day – 2, 3b/4 Lab                                     

 Main focus –                                                                                                                                                         
                                                    

a) To obtain all 5 points from a weak base strong acid titrations using a pH meter.

b) To verify the 5 points on the graph (well except point 1).

c) To use the Henderson – Hasselbach to answer point 3 questions

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.   

 

 Period 2: 

1. pKa’s of Acid Base indicators explained using the buffer equation – Henderson – Hasselbalch

2. Review last nights homework and previous nights assignment that we completed before we begain looking at titration curves.YOU MUST BE ABLE TO IDENTIFY which Points ( 1 – 5 ) on the titration graph you are working with.  

Acid Bases Pre-Titration key p.pdf                                                                                           View Download

Acid Base Lab Titration Graph Questions Key NEW .pdf
View Download
 

3. We will verify Point three on Lab 11 as an example of calculating with our buffer equation.

4. We begin Buffer problems (Blood buffer example) worksheet to practice with point three problems.  I will explain the blood buffer in detail tomorrow.

Buffer Problems – Point 3 problems.pdf
View Download

Buffer Problems – Point 3 problems Key.pdf 
View Download

Period 3b/4: Collect Lab 11

1 – 2.  Same as above.

3BLOOD BUFFER/BUFFER REVIEW – 

Work on Point three problems using Blood buffer example:

Buffer Problems – Point 3 problems.pdf
View Download

Buffer Problems – Point 3 problems Key.pdf 
View Download

 

4.  Lab 12 – Weak Base – Strong Acid Titration – Drop Counters

 

                                                                                                                    

_________________________________________________

ACID and Base NOTES – Blood Buffer

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?
 

Today’s Notes:

From this Last nights homework:

Reaction during the titration – Driven by the strong Acid to completion to the equivalence point
                        
                                       H3O+      +     C6H7O2–           – –>       HC6H7O         +      H2
 
                      strong acid      Weak Conjugate Base      —>    stronger conjugate acid                                                                                         
                          Reaction that occurs at the equivalence point – Equilibrium reached (NOT DRIVEN)
 
                                    HC6H7O2     +    H2O    <—>     C6H7O2-1       +       H3O+
                                      
               conjugate acid ionizes water                                 Lowers pH at equivalence
                                
       
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
~Last nights HW
   pH  <7 @ equivalence                Conjugate Acid produced reacts with water
to produce H3O+
            

Determining Ka, Indicator worksheet review:  Today’s lesson with indicators and pKa’s

 
Determining pKa and Indicators.pdf
View Download
 
Determine Ka and Indicator key p.pdf

___________________________________________________________                                                         jump to:  top                                            11/28 – Wednesday’s Homework: –                                                                                                                                                                                        

1. Please complete the Buffer problems worksheet that we started in class and review with key. If we completed it in class you can skip this step.

Buffer Problems – Point 3 problems.pdf
View Download

 
Buffer Problems – Point 3 problems Key.pdf 
View Download
 
 2. Please predict the following the 5 points on piece of graph paper given the following titration. 
You will be predicting the titration curve from the information given below.  It is essentially the an assignment that is the opposite of what we have been doing with our Titration Curves. Show all work for each point and sketch the curve from the points that you determine from calculation using the information below. This is a lot like what our homework last night. This will be collected tomorrow. There is no form for this assignment.    
 
Point 1 = initial pH = 11.4 (given)
Point 2 = half equivalence
Point 3 = buffer position (when 8.0 ml of titrant has been added )
Point 4 = equivalence point
Point 5 = final pH.                                                                                                                                                               
   
Your graph will predict the titration curve for the following titration:                                                                                                                                                                                                                                                                                                                                                                             25.0 ml of a 0.30 M NH3 solution is titrated with a
                                                  total of 38 ml of a 0.25 M solution of HCl
       
You will need the following additional data to complete the prediction:                                                                                                                                                                                                                                                                                                                                               The Ka of NH4+ = 5.6 x 10-10 
      The initial pH of the analyte solution is pH = 11.4
      The pH at the equivalence point = 4.2   
      Please predict point 3 when 8.0 ml  of titrant has been added                                                                                                                                                                                                                                                                                                                  
Weak Base Strong Acid Titration Prediction graph paper.pdf                                                                                  View Download                            

 

 

____________________________________________________________________________          Jump toThursday Homework /top           11/30 – Thursday – A Day – 2/3a Lab, 4                                                                     

Main focus –                                                                                                                                                                                                                                                                                                                                             a) To perform a Weak Base Strong Acid titration and calculate the unknown concentration of the weak base the using the titration curves using pH probes and drop counters.

b) To perform a Weak Base Strong Acid Titration and determine its endpoint using an acid base indicator.

 

Period 2/3a:

1. A quick review of the Titration Quiz from last night. 

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

2.  Lab 12 – Weak acid Base Titration

a) drop counters and ph probes to produce graph and calculate the unknown concentration of the weak base.

b) Determine the endpoint of the titration using the acid base indicators and calculate the concentration of the weak base.

c) compare the concentration of the unknown by both methods

d) verify all points on graph (except #1)

Period 4

1. A quick review of the Titration Quiz from last night. 

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

2.  Lab 12 – Weak acid Base Titration

– will only get to completing part 1.

                                                         

__________________________________________________________________________                                                                                                      Lab 1 2 – Weak Base / Strong Acid Titration

Like the other acid base titrations we will generate a graph of pH vs volume of titrant and identify/verify points.
This will be part A. Part B will be another titration with the same chemicals but we will use acid base indicators to determine the endpoint. Both part A and part B will allow for the calculation of the molarity of the base.  We will compare both values as part of the lab. The second titration data will be collected on the back of your graph from part A.
 
Part A:  Titration curve generated from pH probes and drop counters.
Part B:  Titration using Acid Base indicators.
                                                   
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
     
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 weak base.
3: Determine the end point of the titration using an appropriate acid/base indicator from the list below.
(Identify on the graph and write the indicator chosen.)
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
8: Write the net-ion reaction.
9: Determine the Ka of the Acid.

10. Confirm the pH of point 3 when 12 ml of acid was added to the weak base.  

_______________________________________________________                                                                    jump to:  top                    11/30 – Thursday’s Homework: – 

1.  Please complete Lab 12 (– ONLY FOR PERIOD 2 Students) based on the lab requirements posted above.  Please write right on the printed graph and clearly label your work with numbers.

Period 4 will complete lab 12 in class!

2.  Tomorrow I will collect another acid base prediction graph paper quiz.

Graph a titration curve take home quiz. – Due in Class.

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) Chemical reaction at the equivalence that supports your estimated pH at point #4
The pH at the equivalence  point will be either be above or below or at 7. Please write the chemical reaction that supports your choice.  Hint: Think of the conjugate acid/base that is being produced as the titration proceeds.
 
    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                                         pKa
bromcresol geen        4.7
litmus 6.5
Thymol blue 8.9
 
 Blank Worksheet:
Design a Titration with HF and NaOH new.pdf

View Download

                                                                                                                                                                                    Please use our last prediction titration to review:

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

   

__________________________________________________________________                                Jump toFriday Homework /top 
12/1 – Friday – B Day – 2, 3b/4 Lab                                     

Main focus –        

 

a) To perform a weak base strong acid titration using an acid /base indicator to determine its endpoint.

b) To determine an appropriate indicator for an acid base titration.

c)  To predict the chemical reaction that is responsible for the pH at equivalence.

 

Period 2 –Collect Prediction quiz 2   

1.  Review the last 2 Prediction quizzes

– Focused on point 3, Net ion reaction, pH at equivalence chemical reaction

2.  Lab 12 – Part 2 – 

Titrate same weak base with same strong acid as yesterday BUT using only the chemical indicator of choice to reach endpoint.

Period 3b/4 – Collect Prediction quiz 2 

1. Complete the Lab 12 – part 1

2.  Review the last 2 Prediction quizzes

– Focused on point 3, Net ion reaction, pH at equivalence chemical reaction

3.  Lab 12 – Part 2 – 

Titrate same weak base with same strong acid as yesterday BUT using only the chemical indicator of choice to reach endpoint.

 

 
                                                                                                                       

_________________________________________________

ACID and Base NOTES – pH at Equivalence

Today’s Notes:

From Lab 12:

Reaction during the titration – Driven by the strong Acid to completion to the equivalence point
                        
                              H3O+         +             NH3                 – –>             NH4+             +           H2
 
                      strong acid      Weak Conjugate Base      —>    stronger conjugate acid                                                                                         
Reaction that occurs at the equivalence point when all the weak base has been driven to completion by the STRONG ACID (HCl):   
 
At the equivalence:   0% NH3 left in the beaker and 100% NH4+ remains and some of it reacts with water!
 
Equilibrium reached (NOT DRIVEN) because all of the Strong Acid has been neutralized!
 
                                    NH4+     +      H2O       <—>        NH3        +       H3O+
                                      
               conjugate acid ionizes water                                 Lowers pH at equivalence
                                

 

From NaOH and HF Prediction Quiz:

Reaction during the titration – Driven by the strong Acid to completion to the equivalence point
                        
                              OH         +                 HF                  – –>                   F             +           H2
 
                      Strong Base      Weak Conjugate Acid      —>    stronger conjugate Base                                                                                         
Reaction that occurs at the equivalence point when all the weak base has been driven to completion by the STRONG ACID (HCl):   
 
At the equivalence:   0% HF left in the beaker and 100% F remains and some of it reacts with water!
 
Equilibrium reached (NOT DRIVEN) because all of the Strong Base has been neutralized!
 
                                    F         +        H2O        <—>          HF        +        OH
                                      
               conjugate base ionizes water                                 Raises pH at equivalence
                                

     

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+
            

__________________________________________________________________________                                                                                                      Lab 1 2 – Weak Base / Strong Acid Titration

Like the other acid base titrations we will generate a graph of pH vs volume of titrant and identify/verify points.
This will be part A. Part B will be another titration with the same chemicals but we will use acid base indicators to determine the endpoint. Both part A and part B will allow for the calculation of the molarity of the base.  We will compare both values as part of the lab. The second titration data will be collected on the back of your graph from part A.
 
Part A:  Titration curve generated from pH probes and drop counters.
Part B:  Titration using Acid Base indicators.
                                                   
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
     
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 weak base.
3: Determine the end point of the titration using an appropriate acid/base indicator from the list below.
(Identify on the graph and write the indicator chosen.)
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
8: Write the net-ion reaction.
9: Determine the Ka of the Acid.

10. Confirm the pH of point 3 when 12 ml of acid was added to the weak base.  

______________________________________________                                                                                  jump to:  top                                   12/1 – Friday 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
View Download
 
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 IF YOU THINK YOU NEED TO!!:                                                                                                                                                                                                                            
Acid Base Lab Titration Graph Questions.pdf
 
Acid Base Lab Titration Graph questions Key p .pdf
View Download
 
Link to the Review video for the Acid Base Lab Titration Graph Question.pdf:  https://youtu.be/FnK3DBJIyp4                                                                                     
 
4. Study for test Monday 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
View Download
 
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
View Download 
 
Intro Acid Bases Packet Key 1718 p.pdf
View Download
 
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
View Download
                                                                                                                                                                                                                                       6. Neutralization problems (Pre- neutralization worksheet)
 
Acid Base Pre- Titration .pdf
View Download
                                                                                                                                                                                              Acid Bases Pre-Titration key p.pdf
View Download
 
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 link:                                                                                                                                                                    https://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
View Download
 
Determine Ka and Indicator key p.pdf
View Download
 
11. Writing Net Ion reactions – video review link:https://youtu.be/q-cbacn16p0
 
Writing Net Ion Acid Base Reactions.pdf
 
Stiochiometry 5a – Acid Base Reactions new.pdf
View Download 
 
Stiochiometry 5a – Acid Base Reactions new Key.pdf
View Download 
 
12. Review of the Today’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: Form not Updated for 23-24 yet!!!