AP Chem – Q2 – week 5 – 21-22 | Mr. Grodski Chemistry

Q2 : Week 5 – 12/12 – 12/16

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12/5 – Monday – A Day – 2/3a Lab, 4 Jump to: Monday Homework

Main focus –

a) To begin Lab 14 – The amount of aspirin in a Bayer tablet.

b) To meet Lab assistant Ben

Period 2/3a:

1. Complete your design and execute!

2. Make strong base / strong acid solutions – Consider the fact that you have 100.0 ml volumetric flasks and you need some of the base you made to standardize with KHP. The arbitrary values you decide on are very important!!

3. Standardization of KHP

4. Final Titrations –

a) Heat the aspirin solution with alcohol and base solution AND KEEP WARM for about 15 minutes while you do other things. Boiling will denature the organic reactants!!! You must monitor the heating.

Period 4:

1. Complete your design and execute!

2. Make your acid and base solutions – Consider the fact that you have 100.0 ml volumetric flasks and you need some of the base you made to standardize with KHP. The arbitrary values you decide on are very important!!

3. The Standardization of NaOH with KHP Titration.

4. Final Titrations –

a) Heat the aspirin solution with alcohol and base solution AND KEEP WARM for about 15 minutes while you do other things. Boiling will denature the organic reactants!!! You must monitor the heating.

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Lab 14 – The Determination of aspirin in a Bayer tablet

You will be graded on how your lab group will design a lab (back titration) to determine the milligrams of aspirin in a single bayer tablet. You will design the lab in the same fashion as I designed the TUMS lab using YOUR arbitrary values that you design.. Last weeks form of Alleve you completed an assignment that was a theoretical lab that determined the milligrams of another active ingredient. You may want to revisit that form or its key. Hint: Both are weak acids.

Molecular Mass of Aspirin: 180.158 g/mole

You will determine the milligrams of aspirin by using 2 tablets of Bayer. Please look at the molecular structures of aspirin below to begin your lab design. Acetylsalicylic acid (aspirin) gets hydrolyzed into 2 components in water.

This is a slow reaction that can be increased by temperature and excess chemical (Le Chateliers principle).

Identification of organic acids can done by Table R in our Regents Chemistry reference tables:

The mechanism for the hydrolysis of aspirin is as follows:

C₇H₆O₃ + C₂H₄O₂ + 2OH^– → C₇H₅O₃^– + C₂H₃O₂^– + 2H₂0

1. Aspirin does not dissolve very well in water due to the hydrophobic benzene ring thus we will use 20 ml of ethanol CH3CH2OH added to the crushed tablets. We will add a stirring bar and stir the solution for a few minutes.

2. After adding ethanol, you will add 3 drops of phenolphthalein to a small erlenmeyer flask.

3. Add the excess chemical that you designed. Careful with the stoichiometry.

4. HEAT THE SOLUTION IN A HOT WATER BATH! DO NOT HEAT DIRECTLY as ethanol is flammable!

5. Observe the color change of the phenolphthalien.

What does aspirin do? It block the productions of prostaglandins. It is another example of NSAIDS. Non-steroidal anti-inflammatory drugs

Cyclooxygenase (COX) ——–> aspirin blocks production of ——> Prostaglandins

aspirin is a competitive inhibitor

Thromboxane Prostacyclin

formation of clotting reduction of blood clotting

narrowing of blood vessels dilation of blood vessels

-Leads to less blood clotting

-Leads to less inflammation

Lab 14 – Aspirin Lab Test Requirements:

a: Using the Google Doc that is shared individually that I have sent, start determining the procedure necessary to determine the amount of aspirin in a Bayer tablet.

USE THE TUMS LAB AS A GUIDE and the Aleve form as your guide!

b: Understanding Lab 13 will help here. You need to figure out what chemicals you need and what their Molarities will need to be to successfully titrate aspirin.

You will need to complete preliminary calculations that will determine the theoretical amount of the other chemicals needed to perform the titration, in the same fashion as we did with Lab 13.

c: You will perform the titration and determine the milligrams of the active ingredient per tablet as a lab group in a later date.

d: I will look over your procedure and preliminary calculations and give you the go ahead to perform the Lab test.

e: In your Shared Lab group Doc, I expect

In this Lab Test I am require the following:

1. Title Page.

2. Objective.

3. materials

4.a detailed procedure

a) Design of lab – (arbitrary values decided on)

b) Calculations and steps to make certain solutions required in Lab.

c) Steps in the actual lab

5. typed calculations page that report the milligrams of aspirin. Tablet the final result. (DO NOT FORGET ANY CHEMICAL REACTIONS!)

No Background, Results section, Data Table or Conclusion necessary!

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12/12 – Monday’s Homework: –

1. Begin your Lab 14 write-up. I have shared a google doc with you to complete the assignment with. The requirements are given above. Please get on this as I will be moving on to the next stoichiometry topic very soon. Our next connecting idea is volumetric titrations with redox reactions. It is very similar with acid base titrations except we are not matching protons with hydroxides. We are matching the electrons lost to the electrons gained.

_______________________________________________________________ Jump to: Tuesday Homework / top

12/13 – Tuesday – B Day – 2, 3b Lab/4

Main focus –

a) To Continue with determining the milligram of Aspirin in a Bayer tablet.

b) To Review balancing redox reactions in an acid or basic solution (HW).

Period 2:

1. Make your solutions and Standardize.

2. Crush Tabs and heat.

3. Back Titrate.

Period 3b/4:

1. Make your solutions and Standardize.

2. Crush Tabs and heat.

3. Back Titrate.

Lab 14 Hints:

a) Make the HCl solution needed to back titrate

b) crush the aspirin tab(s)

c) Add distilled water and heat solution for 10 – 15 minutes.

d) Add your base solution (in excess).

e) stir using the stirring bar and the magnetic stirrer for a few minutes. Solution should still be warm.

f) Back titrate with HCl solution. Make sure you rinse the buret with HCl as it had a base in it previously!

e) calculate the milligrams of aspirin in your tabs!

Notes For the Homework:

Connections:

The Balancing of complex Redox equations was a skill that was introduced this summer. We are revisiting redox again! It was introduced early in the year to splash you into the course, using voltaic cells (batteries) and electrolytic cells (electrolysis and electroplating). Now we will focus on redox reactions that are NOT part of a electrochemical cell and these complex reactions will make more sense when we balance them with the college method. This method still works for our simple half reactions that we saw in September but will provide more insight on their structure. Most of these complex redox reactions require an acidic or basic environment so it makes sense that I reintroduce them now, after we have studied acid/base concepts.

Most chemical reactions are redox in nature and I want To Do more stoichiometry Labs with redox in the analytical chemistry section of the course.

When you think about it most chemical reactions are either redox, acid/base, or precipitation reactions and through our work together we have studied all three since September.

Redox:

3 Mn⁺² (aq) + CrO₇^-2 (aq) + 2H⁺(aq) —–> 3 MnO₂ (s) + 2Cr⁺³ (aq) + H₂O (l)

precipitate

Acid Base:

NH₃ (aq) + CO₂ (aq) + H₂O (l) —-> HCO₃^-1(aq) + NH₄⁺ (aq)

base acid

Precipitation Reaction:

Ca⁺² (aq) + CO₃^-2(aq) —–> CaCO₃ (s)

precipitate

Now most reactions are one of these three types but as you can see above sometimes these reactions are a combination of each other. Notice that in the Redox reaction we have protons H⁺ (acid/base) and in the example above a precipitate ( MnO₂ (s) ) is made. Redox reactions can also occur in Basic conditions as well.

Your homework will include balancing redox reactions in acidic and basic solutions. Why? Remember that protons produced by acids will pull electrons from chemical species that will spontaneously lose (oxidize) or AND hydroxides produced by bases will push its electrons onto chemical species that will spontaneously accept (reduce) them. The acid/base component of the complex redox equation that we will balance tonight is required to drive these reactions to completion. In order to use stoichiometry we need reactions to be driven forward till the limiting reactant runs out! We need to stay way from equilibrium!

ALSO the first 2 steps of the hydrolysis of aspirin is actually a redox reaction catalyzed by the presence of a the hydroxide ion!!!! Protons (H⁺) also catalyze these complex redox reactions and so we will learn (review from the summer) how to balance these advanced redox reactions in the presence of Acid or Base!!

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12/13 – Tuesday’s Homework: –

1. Continue with Lab write-up for Lab 14.

2. Please read the connections above.

3. Please complete side 1 and 2 (questions 1 – 5) of the Redox 3 balancing redox equations.pdf worksheet and review with the key. You will need to view the How to balance redox reaction in acid environment (College version) lecture for reactions 1 – 3 and How to balance redox reaction in basic environment for question 4. Please use the key below to help review the homework, especially reaction 5.

Notes on how to balance complex reactions in acidic and basic solutions:

Redox 2- balancing redox equations NOTES.pdf
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Redox 3 balancing redox equations.pdf
View Download

Redox 3 balancing redox equations key.pdf
View Download

How to balance redox reaction in acid environment (College version) Lecture:

Questions 1 – 3 reviewed.

How to balance redox reaction in basic environment (College version) Lecture:

Question 4 reviewed.

End of Tuesday..

_____________________________________________________________________ Jump to: Wednesday Homework / top

12/14 – Wednesday – A Day – 2/3a Lab, 4

Main focus –

a) To identify strong oxidizing agents.

b) To balance redox reactions in acidic or basic solutions

c) T0 use the standard reduction potential table to predict spontaneity especially with protons from acids and metals.

Period 2:

1. Redox 2.0 – Redox with more advanced reactions and with Volumetric Titration.

New Activity: used a 0.25 M hydrogen peroxide solution by measuring 5.1 ml of 2 serial dilution starting with 9.8M (which is the concentration of 30% hydrogen peroxide). Added 2.5 ml of 6M sulfuric acid to analyte.

0.01 M potassium permanganate was used.

Goal: 10 ml of Titrant = 10 ml of analyte so that 0.01 x .2.5 (mole ratio) = .025 M of hydrogen peroxide.

Redox Volumetric Titration Activity.pdf View Download

A) Titrate hydrogen peroxide with potassium permanganate. Determine the volume of potassium permaganate that is needed to titrate hydrogen peroxide.

B) Balance the reaction, identify the oxidizing and reducing agents, and determine the concentration of the postassium permagante.

C) Revisit the Standard Reduction Table THAT INCLUDES STRONG Oxidizing agents like potassium permaganate. Discuss their structure.

D) Look at Nitrates and identify their potential as an oxidizing agent. Revisit the standard cell experiment and discuss the how the proton is a strong enough oxidizing agent for most metals but not for Cu.

How does nitric acid react with copper?

Demo?

2. Final Lab 14 comments and discussion

Period 3/4:

1. Final Lab 14 comments and discussion

2. Redox 2.0 begins

3. Table T

Today’s Notes:

1. Lets continue our discussion with more Redox reactions that require acidic or basic conditions.

Lets remember that oxidizing agent or the oxidizer is a chemical that drives others chemical into oxidizing (losing electrons).

The oxidizing agent gets reduced gains electrons as it forces other chemicals to lose electrons.

Strong Oxidizers or oxidizing agents are easily identified by their arrangement of electron sinks. Usually a group of very electronegative oxygens surrounded by a highly charged positive ion (that is small) . Due to Coulomb’s law, these chemical force chemicals to lose electrons and and can be very dangerous.

Examples: KMnO₄, KCr₂O₇ , H₂O₂ , KNO₃, NH₄ClO₄

Ammonium dichromate, (NH₄)₂Cr₂O₇, decomposes when heated to produce chromium(III) oxide [Cr₂O₃], nitrogen gas, and water vapor:

(NH₄)₂Cr₂O₇(s) ——> Cr₂O₃(s) + N₂(g) + 4H₂O(g)

I have included some of these strong oxidizers like dichromate ion above into the Standard net potential table that I gave you earlier this year:

Table T with Net potential table 1718.pdf

View Download

The proton that is dissociated from acids is heat sinking missile for the loosely held electrons of metal and it causes the oxidation (loss of electron) of the metal and thus H⁺ is the oxidizing agent. It however it not strong enough to pull electrons from all metals.

The standard cell experiment that helped us determine the voltages of the half reactions in the Standard Reduction Table uses the proton (H⁺) as the oxidizer to force the other chemical reduce BUT it is not strong enough to make all chemical oxidize and thus explains why there is change in the signs in the standard reduction table around the reaction with protons (H⁺):

Notice the that 2 protons oxidize other chemicals and thus gain 2 electrons to produce hydrogen gas.

Notice that all half reactions below it have negative standard potentials because these half reactions are MORE spontaneous in the Reverse Reaction thus they are better at getting oxidized, which means the proton is ONLY a strong enough oxidizing agent to those chemicals (metals) on the right and below the standard cell half reaction.

This means acids that only produce protons can only produce hydrogen gas with those metals reactive enough (below it ).

Example: HCl can produce hydrogen gas with Pb (E⁰cell = 0.13) but not with Cu (E⁰cell = – 0.34)

New York State uses Table J instead of a “real Net potential table’!

So copper is not reactive in acids?? Well its not reactive with protons BUT it will react with stronger oxidizing agent than H+!

From the last August Chemistry Regents:

Today’s lesson:

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12/14 – Wednesday Homework: –

1. Complete your write – up of the Aspirin Lab 14 – It is due Monday! 2. Please complete the following released AP problem with we using the video below:

Stoichoimetry 7 – 2010B 1819.pdf
View Download

An older key but it will do the trick:

Stoichoimetry 7 – 2010B AP Key p.pdf
View Download

2. Review of the Released REdox AP Question:

End of Wednesday.

Jump to: Thursday Homework / top
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12/15 – Thursday – B Day – 2, 3b Lab/4

Main focus –

a) To identify spontaneous reactions through standard reduction potentials and terrible Table J!

a) To balance Redox reactions in acid or base solutions and use the reactions in Volumetric Titrations.

Period 2:

1. Homework review – Hey was there a back titration in the homework? Can you balance a redox reaction – college method? The methods used in the problems in the back problems of last nights homework are the same methods used in the TUMS and Aspirin lab!!!!

2. Standard Reduction Table vs. Table J , Reactivity of Metals

3. Determining Spontaneous Reactions based on strength of agents with both tables

Period 3b.4:

2. Standard Reduction Table vs. Table J , Reactivity of Metals

– penny demo, strong oxidizer molecular structure, nitrate ion acts on copper

3. LAB 15 – pre lab and completed the Standardization – Final Titration tomorrow.

Oxidation of a Post 1981 – Penny Demo –

Penny Demo:

Using our understanding spontaneity we can hollow out a post 1981 penny.

The proton is heat sinking missile for the loosely held electrons of the metal and it cause the oxidation (loss of electron) of the metal and thus H⁺ is the oxidizing agent. It however it not strong enough to pull electrons from all metals.

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Lab 15 – The Determination of the Concentration Oxalic Acid by a Volumetric Redox Titration

Leafy greens, legumes, and most other plant foods contain a nutrient called oxalate or oxalic acid. It’s a naturally occurring chemical you get through your diet. The body also produces it as waste. Foods rich in oxalates also contain other nutrients that your body needs for good health.

When oxalic acid mixes with other minerals, it forms oxalate. People regularly use the two terms interchangeably to refer to the same thing. Your body produces oxalate and also gets it from food sources. Vitamin C changes to oxalate when your body processes it.

When you consume foods containing oxalate, the compound attaches itself to minerals to make other minerals. These include iron oxalate and calcium oxalate. The process happens in the colon most of the time and sometimes in the kidneys.

The body then removes the elements through stool or urine. For people with high levels of sensitivity, diets high in oxalates can cause kidney stones. They also increase their risk of other health problems.

WebMd

Lab 15 – Titration of Oxalic acid.pdf

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MnO₄^– is a purple compound due to the Mn⁺⁷ ion and when it gets reduced (gains electrons by

acting as an oxidizing agent) and Mn⁺² is colorless. This is significant as we can use the color change to reach an equivalence point IN TERMS of Electrons to end the redox titration. That is when the purple persists from the titrant (MnO₄^–) for at least 30 seconds all moles the electrons from the oxalic acid have been transferred to the MnO₄^–_.

We are not using an acid base indicator! We are using a property of metal ions that have high charges = crystal field theory. Crystal field theory provides colors to metals that have high coulombic attractions. Metals that a have high enough charge to create this affect are transitional.

MnO₄^– ——> Mn⁺²

purple colorless

Because the KMnO4 is a very strong oxidizing agent (1.52 volts) we need to standardize it to know exactly what its concentration is BEFORE we titrate the oxalic acid because it can pull electrons from many chemicals (that are below it and to the right in the standard reduction table).

Today’s Lesson: sort of ..(I spent more time with the Hw review to Link Back titrations in the homework with the back titrations in the LAB!!! Come together…..

End of Wednesday.

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12/15 – Thursday Homework: –

Period 2 class – Do not complete Lab 15 – we work on it tomorrow in class.

1. Please complete the following worksheets that we started in class and review their keys:

I may collect something tomorrow.

If you need help with these concepts from the worksheets below please view the posted class lectures from today and yesterday. They really focus on these basic skills.

Make Sure YOU TRY TO ANSWER these questions with the net potential table AND

with TABLE J (regents Table).

Redox – Activity Series net potentials.pdf
View Download

Redox – Activity Series net potentials KEY.pdf
View Download

_______________________________________________________________ Jump to: Friday Homework / top

12/16 – Friday – A Day – 2/3a Lab, 4

Main focus –

a) To complete Lab 15 – Redox Volumetric Titration.

b) To Review more complex Redox reactions and applications.

Period 2/3:

1. Lab 15 – Start and Complete

2. Review Redox reactions/Demo:

a) Reactivity of metals demo video —> Penny Demo.

b) Tarnished Silver Tray

c) Copper and Nitric Acid demo

Period 4:

1. Start and Complete Lab 15.

2. Review Redox reactions/Demo:

a) Reactivity of metals demo video —> Penny Demo.

b) Tarnished Silver Tray

c) Copper and Nitric Acid demo

Reactivity series Lab – Acid added to metals (the action of acid is actually a redox reaction):

Metal(s) + 2 HCl => Metal Chloride (aq) + H₂ (g)

Ex: Mg (s) + 2HCl => MgCl₂ (aq) + H₂ (g)

NET ION: Mg(s) + 2H⁺ => Mg⁺² + H₂ (g)

The proton is a heat sinking missile for the loosely held electrons of the metal and it cause the oxidation (loss of electron) of the metal and thus H⁺ is the oxidizing agent. It however it not strong enough to pull electrons from all metals. The standard reduction potential table OR unfortunately Table J can tell us the reactivity of the proton of the metal.

Reactivity of metals in HCl and water Demo/lab:

The reactivity of metals in acid and water (their ability to oxidize) can be predicted by both Standard Reduction Table and the Table J.

Nitric Acid and Copper Demo:

Oxidation of a Post 1981 – Penny Demo –

Penny Demo:

Using our understanding spontaneity we can hollow out a post 1981 penny.

3: Silver plate non tarnish demo:

There are 2 reactions in this reaction that removes the tarnish (rust) from the oxidation effect of sulfur in our air that usually results from the breakdown of organic matter (dead animals and plants).

Silver exposed to Air that has hydrogen sulfide: 2 Ag(s) + H₂S(g) —> Ag2S(s) + H2(g)

tarnish

#1 3 Ag₂S(s) + 2 Al(s)+ 3 H₂O(l) —> 6 Ag(s) + Al₂O₃(s) + 3 H₂S(aq)

#2 3 NaHCO₃(aq) + 3 H₂S(aq) —-> 3 NaHS(aq) + 3 H₂O(l) + 3 CO₂(g)

What type of reactions are these?

4: Underwater fireworks:

#1 2KMnO₄ (s) + 16HCl —> 2 KCl + 2MnCl₂ (aq) + 8 H₂O (l) + 5Cl₂ (g)

#2 CaC₂ + 2H₂O —> C₂H₂ + Ca(OH)₂

#3 C₂H₂ + Cl₂ —> 2HCl + 2C + heat (light)

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Lab 15 – The Determination of the Concentration Oxalic Acid by a Volumetric Redox Titration

WebMd

Lab 15 – Titration of Oxalic acid.pdf

View Download

MnO₄^– is a purple compound due to the Mn⁺⁷ ion and when it gets reduced (gains electrons by

MnO₄^– ——> Mn⁺²

purple colorless

Lab 15 : Review – Live Stream from last year.

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12/16 – Friday Homework: –

*Some students have asked for the net ion reaction to the Aspirin Lab:

C₇H₆O₃ + C₂H₄O₂ + 2OH^–→ C₇H₅O₃^– + C₂H₃O₂^– + 2H₂0

1. Please View the class lecture on crystal field theory and Spectrophotometry.

2. Please complete the AP free response question below (no Grodski changes!) and review with the key below. You will need to view my tutorial video to follow along with me using the worksheet below to completely understand the spectrophotometry procedure.

Can you guess what your next lab will include?

Spectrophotometry AP question 2 – 2003-1.pdf
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Spectrophotometry AP question 2 – 2003 AP Key.pdf
View Download

3. Complete the form.

1: Crystal Field theory and Spectrophotometry class lecture:

2: Spectrophotometry worksheet review lecture:

3: Spectrophotometry Intro Form::

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End of Thursday….

Spectrophotometry Presentation that was in the lecture:

End of week 5!