Archive – week 10 – 19-20
Week of 11/5- 11/9 –
11/5 – Monday – period 2-
*Okay i made an error on the last net ion reaction of the front side of the weekends homework. The product of NH3 and H3O+ is NH4+ and water (H2O)! Sorry about that! I was trying to illustrate the reaction between a Strong Acid (H3O+) and a weak base (NH3) thus water would be made in the neutralization reaction. (Thanks Josh Kaplan 2018)
1. RAT #1 Acid Base Intro Basics
period 2/3 –
demo straw and washing soda..
1. RAT #1 Acid Base Intro Basics
2. Review
Stiochiometry 5a – Acid Base Reactions new worksheet.
Stiochiometry 5a – Acid Base Reactions new Key.pdf
3. Classwork:
Acid Bases Pre – Titration worksheet and review with key below.
11/5 – Monday Homework –
1. Please review the Today’s RAT . Expect a new Rat Tomorrow that will include the same information but includes acid/base stiochiometry
.
Mondays’ Blank RAT
Rat #1 – Acid Bade Intro Basic Review:
2: Please complete Acid Bases Pre – Titration worksheet and review with key below. Period 4 may have started this worksheet already but please complete it.
3. Please complete the
Stiochiometry 5a – Acid Base Reactions new.pdf worksheet with (side 1 and 2) using the posted videos below.
*Remember that soluble salts (aq) were never written together in NET ION EQUATIONS while the precipitate (s) are because they do exist in a crystal together. In Acid/Base the “soluble ” compound is the “Strong” Acid or Base because they completely dissociate just like soluble salts, however weak acids and bases are NOT completely dissociated thus must be written together. WATER IS A NEVER Written dissociated because they barely dissociate!!!
Tutorial on Stoichiometry 5a – Acid Base Reactions new.pdf worksheets:
New Side One Lecture : Acid/Base Net Ion Reaction Review:
Okay i made an error on the last net ion reaction. The product of NH3 and H3O+ is NH4+ and water (H2O)! Sorry about that! I was trying to illustrate the reaction between a Strong Acid (H3O+) and a weak base (NH3) thus water would be made in the neutralization reaction. (Thanks Josh Kaplan 2018)
New Side 2 Lecture : Acid/Base Titration problems:
11/6 – Tuesday period 2/3 –
1. RAT #2 Acid Base Intro Basics and Titration
Lab:
2. Lab 10 – Strong Acid/Base Volumetric Titration
with phenolphthalein & pH probes
period 4 –
1. RAT #2 Acid Base Intro Basics and Titration
2. Lab 10 – Strong Acid/Base Volumetric Titration
with phenolphthalein & pH probes – INTRO
11/6 – Tuesday – Homework:
1. Period 2/3 – students
1. Complete Lab 10 on your Graph with the instructions and video posted below:
2. Period 4 students –
Please make a key explaining the correct answers for each question.
SHOW ALL WORK!!! If it is done accurately and completely explained I will give you a 100 for a quiz grade (X3)
I will link you a google doc today and you will use that doc to write solutions for each questions.
I will post a pdf of the today’s Rat so that you can use the image in your Key.
You can link your lab group and work as a team if you would like.
Lab 10 INSTRUCTIONS-
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 50.0 ml of Strong Acid (HCl) in the small beaker was titrated with 0.06M Strong Base , Ca(OH2).
Objectives –
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.
Please use the lecture below AND THE KEY to the video to complete the lab directly on the printed Titration Graph of the Strong base/Strong Acid that you did today.
LAB 10 : Strong Base – Strong Acid Titration lab write-up:
The video uses the same titration but a different amounts and concentrations.
In this Video I am using 0.03 M of Ca(OH)2 and 25 ml of unknown concentration of HCl. I have posted a key for this video so that you can see my calculations for this specific titration. Again you used 0.06 M Ca(OH)2 not 0.03 M and we started with 50.0 ml HCl in the beaker and added a total of 50 ml of base at the conclusion of the titration.
Key for this assignment: Remember that I am using different concentrations and volume in this titration but the Acid and Base are the same. You should be able to follow how I calculated my values for THIS titration curve and apply to your values you obtained today,
11/7 – Wednesday – period 2
1. Do not hand in Lab 10 – Strong Acid (HCl) was titrated with 0.06M Strong Base (Ca(OH)2)
We need to compare this graph with a new titration today.
2. Lab 11 – Weak Acid (HC2H3O2) titrated with 0.06M Strong Base, Ca(OH2)
We will complete this titration right away and print out graphs.
3. Back at out seat we will compare and contrast both graphs, and I will walk you through how to
complete this Lab.
What is similar and dissimilar with these titrations?
a) Starting pH b) Ending pH c) size of the asymptote? d) pH at equivalence e) Buffer region
What is new with this titration?
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.
4 Henderson Hasselbalch Derivation
– period 3/4
1. Lab 10 titration – Strong Acid (HCl) was titrated with 0.06M Strong Base (Ca(OH)2)
2. Complete the Lab 10 at seats together as a class. Lab 10 instructions posted under Tuesday above.
3. Lab 11 titration –
Lab 11 – Weak Acid (HC2H3O2) titrated with 0.06M Strong Base, Ca(OH2)
4. Back at out seat we will compare and contrast both graphs, and I will walk you through how to
complete this Lab.
What is similar and dissimilar with these titrations?
a) Starting pH b) Ending pH c) size of the asymptote? d) pH at equivalence e) Buffer region
What is new with this titration?
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.
Henderson Hasselbalch Derivation
LAB 11 – Requirements
Lab 11 – Weak Acid (HC2H3O2) titrated with 0.06M Strong Base, Ca(OH2)
Objectives –
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. 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.
Lab 11: Lecture: If you want me to walk you through all steps. I will go over step 9 in class tomorrow.
Wednesday NOTES!
**ACID/BASE TITRATION Curve NOTES:
The new skills that we learned from Monday’s/ Tuesday’s Titrations 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.
Consider 2 titrations like the 2 we did yesterday. 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?
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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 ó 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 ð 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 ó H+ + C2H3O2–
Keq = [H+][C2H3O2–] / HC2H3O2
Keq = Very Small
Now because these reactions are very similar (HA ð 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!!!
 |
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.
11/7 – Wednesday – Homework
Period 2 class ONLY:
1. Period 2 Class is to complete the key to the second ACID/BASE RAT.
2. Read todays Notes posted above.
3. Complete Lab 10 and 11 if not completed already. STAPLE BOTH Labs together
Use the instructions and resources that I posted Today (above) to complete.
4. View the lecture posted below and follow along with me using the Determining pKa and Indicators.pdf worksheet below. Try the last question on your own and I will review in class.
Lab 10 & 11 Due Thursday 11/8
Period 3/4 class ONLY:
1. Complete Lab 10 (what we did today directly on the graph).
Use the instructions posted on Tuesday for lab 10.
I have a video that will help you as well as a key’
* You need to understand every objective of this lab!
2. Please complete with me the Determining pKa and Indicators.pdf worksheet. I will post a lecture that will review this worksheet. The last question I would like for you to try on your own and use the key to complete. I will review that problem in class.
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
Determining pKa and Indicators.pdf Lecture video:
End of Wednesday.
11/9 – Thursday- period 2/3- NO ACID BASE TEST TODAY!
1. Review homework:
a) What is the Ka?
b) What is the appropriate indicator?
2. Review Lab 11 – Weak Acid – Strong Base Titration
3. Completed The Design a Titration with HF and NaOH
This is the video review of this worksheet
period 4 –
1. Lab 11 – Weak Acid (HC2H3O2) titrated with 0.06M Strong Base, Ca(OH2)
2. Classwork: Complete the lab on the titration graph
3. Review the final question on the homework
LAB 11 – Requirements
Lab 11 – Weak Acid (HC2H3O2) titrated with 0.06M Strong Base, Ca(OH2)
Objectives –
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. 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.
Lab 11: Lecture: If you want me to walk you through all steps.
11/9 – Thursday – Homework:
1. Study for the Acid / Base test.
2. Please make sure you know how to complete this worksheet that we started (or finished) in period 2/3. For period 4 students you will need to complete for homework. Please use the key or I can walk you through this worksheet with the video below. Period 4 students will have 2 periods tomorrow and I will review BUT you need to fight and get as much out of this worksheet as possible!
*Tomorrows test is a single period ( 2 pages, front and back). You will need all of your skills that you have learned in Acid and Base.
Lecture on classwork problem : Acid Base Lab Titration Graph Questions.pdf
*Tomorrows test is a single period ( 2 pages, front and back). You will need all of your skills that you have learned in Acid and Base.
Video review of the Design a Titration with HF and NaOH: I did this together with period 2 folks.
I will do this for period 4 folks tomorrow!
ACID BASE 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
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:
6. Neutralization problems (Pre- neutralization worksheet)
7. Strong Acid base titration skills – Lab 10 – Lecture posted Tuesday
8. Weak Acid/ Strong Base titration skills – Lab 11 – Lecture posted Wednesday and Thursday
9. Picking an appropriate indicator – Lecture posted Wednesday with NOTES.
10. Calculating the Ka from graph – Lecture posted Wednesday and NOTES.
11. Writing Net Ion reactions
12. AP question example – todays classwork – Lecture posted above
11/10 – Friday – period 2
1. Acid Base Test! – one period test ! (2 pages!)
period 3/4
1. Review Homework/Weak acid – Strong Base Titration
2. Review Wed night Homework – Determining pKa and Indicators.pdf
3. Completed The Design a Titration with HF and NaOH worksheet.
4. Acid Base Test! – one period test ! (2 pages!)
Friday – Weekend Homework:
Please Read this instructions carefully!
1: You are to review the test that I have sent back you with either the key or with the lecture that I have posted. The key will be linked in power school.
2. You are to complete the form below once you have reviewed you test.
Here is a Blank copy of the form you could print:
3: review your work in the form as it will automatically grade and send back a link to a handwritten key.
4: Test TUESDAY – Best out of 2.
Lecture on reviewing Test 3:
THis video will be unlocked Friday afternoon!
TEST 2 review Form: