AP Chem – Q2 – week 6 – 21-22 | Mr. Grodski Chemistry

Q2 : Week 6 – 12/19 – 12/23

<Week 5 – Week 7> Jump to: Tuesday, 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 read all instructions for all assignments.

_________________________________________________________________________________________________________________________________
12/19 – Monday – B Day – 2, 3b Lab/4 Jump to: Monday Homework

Main focus –

a) To Review the concept of Crystal Field Theory

b) To Review Spectrophotometry

c) To begin Lab 16 – % copper in brass

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: 4 Ag + 2H₂S + 0₂ —> 2 Ag₂S + 2 H₂0

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?

Period 2:

1. Demo Review/ Nitric acid copper demo:

2. Crystal Field Theory and Spectrophotometry Review

Period 3b,4:

1. Demo Review/ Nitric acid copper demo:

2. Crystal Field Theory and Spectrophotometry Review

3. Lab 16 begins –

a) dissolve 2 brass shot with nitric acid.

b) Make serial dilutions

Notes For the Crystal Field Theory:

Crystal Field Theory – Explanation of colored solutions from transitional metal complexes

Why was the Cu⁺²ion that was produced by the oxidation of the nitrate ion in the nitric acid that was added to the copper in the demo yesterday produce a blue-green color?

Why does our blood which contains iron (Fe⁺³) have a maroon color?

Why did the permanganate ion (MnO₄^-1) have a purple color in our Volumetric Redox Titration Lab ?

Remember in the permanganate ion there is a Mn⁺⁷ ion.

Why are plants mostly green because the main photosynthetic pigment pigment in chloroplasts chlorophyll absorbs the blue and red part of the visible spectrum. This is part of the negative theory of light (which I will review in a later date).

Gavin Acuri 2019

This is an absorption spectrum from the pigments that were extracted from our Spinach Plants last year.

Notice the these combined pigments in the thylakoid membranes of chloroplasts ABSORB visible light in the Blue and Red parts of the visible spectrum and thus Green is transmitted back to our eyes.

The negative theory of light work with inks and paints.
Green paint is the result of the chemicals in the paint absorbing the red and blue parts of the spectrum due to their electron arrangements around the atoms in the molecules.

Plants appear green because they are receiving green photons ( so that they can transmit them back to you).

What do plants look like when they do not get green photons?

The spectrophotometer above directs a full spectrum of white light at its target and measures what is missing.

Now Chlorophyll, a molecular compound, does not contain a transitional metal and it creates colors by a different theory that we will learn later in the year (pi – stacking).

So what is special about transitional metals that create colored solutions?

Transitional metals have properties that will lead to them absorbing parts of the visible light spectrum which results when their cations form complex ions.

1. They are smaller atoms as they are “transitioning” into nonmetals. They are positioned to the right of the Group 1 (Alkali Metals) and Group 2 (Alkaline Earth metals) and thus have more protons than the more reactive metals.

2. They have multiple oxidation states with some of those oxidation states having large positive values (ex. Mn⁺⁷ in the permanganate ion).

3. They have d orbitals that are not completely filled with electrons that allow for electron transitions. It is these d orbitals that get “split” into 2 distinct energy levels that allow for the the absorption of parts of the visible spectrum that produces the color we see in solutions.

So colors form transitional metal ions in water come from theses complex ions due to the very large Electrostatic Force (Coulombs Law) that draws the oxygen end of water (ligand) into the d orbitals of the metal ions. If the oxygen end is drawn directly into the d orbital it will destabilize (increase in energy) of those orbitals. If the Oxygen end goes in between the d orbitals it does not increase the energy of the those electrons as much and thus the d orbitals which are normally the same energy are now split into 2 different energy levels.

Crystal field theory – Fe+2 solution reacts to Fe+3 with oxygen in flask. Why is it getting cloudy?

I have to make the Fe⁺²solution fresh each day.

3 hours later... (in a bad French accent)

As the Fe⁺² becomes Fe⁺³ the solution has a greater ability to absorb wavelengths of visible light because Fe⁺³ makes a complex ion with water that attracts water with such high Coulombic attractions that the water’s lone pair of electrons are pushed into the iron’s (Fe) d – orbitals directly interfering with some d – orbitals and not others based on their orientation in space. The orbitals that “feel” the oxygens electrons become destabilized (increase in energy) and there is a spit in the energy level between these orbitals that were initially the same energy.

This splitting of d orbital energy levels provides a pathway for electrons to transition to higher energy levels when low energy visible light energy (photons) are absorbed. Not all of the wavelengths of light are absorbed thus the ones that are not absorbed are what we see.

The spectrophotometer picks up the transmittance (which is the what is absorbed or missing from our eye.)

A photon of light of a certain wavelength is absorbed by electrons in lower energy d orbitals that can now transition into higher energy d orbitals (that split due to electrons being pulled directly into the orbitals). The absorbed photon is now missing from the entire spectrum of light that is illuminating the complex and the color shown is what is left.

Spectrophotometry Presentation:

Crystal Field Theory Presentation:

End of week 5!

______________________

Lab 16 – The Percent by Mass of Copper in Brass.

a percent by mass lab – need initial mass at the beginning!

a) Set up your spectrophotometer so that it is calibrated (to water in a cuvette), set to measure

a peak wavelength (with the .40M solution),

b) Make our serial dilutions to calibrate the spectrophotometer

0.40 M (Standard), 0.04M, 0.02 M, 0.01M, 0.005M of Cu(NO₃)₂

c) Place your four cuvettes of KNOWN concentrations into the spectrophotometer from

lowest concentration to highest and type in your concentrations (with Keep button like you

did with the Acid /Base titrations. This is called a Beer’s Law graph. Hit the regression

button to make a line of best fit that will also provide the slope and y – intercept data.

Print this Graph.

d) Dilute the dissolved brass solution (from nitric acid that was added to your brass samples yesterday). You will dilute to 100.0 using a 100.0 ml volumetric flask. Googles and gloves here!

e) Once diluted to a the known volume, 100.0 ml, all you need to know to determine the percent of copper in the brass sample was obtain it concentration. You will now fill a an empty cuvette with this solution.

Place it into the spectrophotometer and determine its Absorbance.

f) Determine solutions concentration (molarity) using the Beer’s Law graph that was made yesterday (by

using linear algebra).

g) Calculate the moles of copper, grams of copper and finally the percent by mass of copper.

Lab 16 – Non-formal– Write-up requirements: This lab will be an individual Slide-up

1. Title Slide – Title of Lab / name / date

2. Background SLIDE– How spectrophotometry works/Notes

3. Objective SLIDE: – To determine the percent by mass of copper in brass.

4. DATA SLIDES:

a) Balance reaction between brass (copper only) and nitric acid (HNO₃ ) on Data page

NO₃^-1 —–> NO₂

Cu ——-> Cu⁺²

b) Data table:

a) mass of Brass Shot total

b) balance nitric acid/calculation

c) Serial dilution calculations

c) Beer’s Law Graph on its own SLIDE – I will post digital copies of each lab

d) final calculation of % by mass of copper in shot – Show all calculations

e) Calculate the absorptivity constant (a) using the absorbance (A) and concentrations (c).

A = a b c

Using the absorbance values from the spectrophotometer (A), the path length ( b = 1 cm ), and the

concentrations of these solutions (c) solve for a with the correct units. Make a chart. These

values that you calculate should be similar as it is a constant.

5. Error analysis SLIDE: The limitation of the lab was based on how well you made the solutions and if the absortivity constant STAYED CONTANT! I will explain once you finish step e.

6. Sources Slide: If needed

I will explain e) on Wednesday!

_____________________________________________________

12/19 – Monday’s Homework: –

1: Please complete the class worksheet with the lecture and or key.

2006 B spectrophotometry question.pdf
View Download

2006 B spectrophotometry question key p.pdf
View Download

2. You can make one more submission to last nights (weekend’s form).

Spectrophometry and 2006 B worksheet review:

Start at 25:50 for the worksheet review. If you want more spectrophometry review please feel free to watch the entire video.

__________________________________________________________________ Jump to: Tuesday Homework / top

12/21 – Tuesday – A Day – 2/3a Lab, 4

Main focus –

a) To continue with the percent by mass of copper in brass lab

b) To Review concepts of spectrophotometry and crystal field theory.

c) To calculate a in A = abc and determine the limitations in spectrophotometry

Period 2/3a:

1. Review the Spectrophotometry Form with key:

Spectrophotometry Intro Form Key.pdf
View Download

2. Complete making the standard solutions from the serial dilution of 0.40 M CuSO4

3. Calibrate the spectrophotometer and run the known sample to create a Beer’s Law Graph.

4. Make the final solution from the dissolved brass.

5. Calculate the percent by mass of copper in the brass sample.

Period 4:

1. Review the Spectrophotometry Form with key

2. Dilute the dissolved brass shot from yesterday into 100.0 ml volumetric flasks.

3. Calibrate Spectrophotometers, create Beer’s Law graph with standard solutions

4. Make a regression line (line of best fit) and determine the slope and y intercept.

5. Run the unknown solution through the spectrophotometer and calculate the Molarity.

6. Determine the % by mass of the copper in the brass shot.

______________________

Lab 16 – The Percent by Mass of Copper in Brass.

a percent by mass lab – need initial mass at the beginning!

a) Set up your spectrophotometer so that it is calibrated (to water in a cuvette), set to measure

a peak wavelength (with the .40M solution),

b) Make our serial dilutions to calibrate the spectrophotometer

0.40 M (Standard), 0.04M, 0.02 M, 0.01M, 0.005M of Cu(NO₃)₂

c) Place your four cuvettes of KNOWN concentrations into the spectrophotometer from

lowest concentration to highest and type in your concentrations (with Keep button like you

did with the Acid /Base titrations. This is called a Beer’s Law graph. Hit the regression

button to make a line of best fit that will also provide the slope and y – intercept data.

Print this Graph.

d) Dilute the dissolved brass solution (from nitric acid that was added to your brass samples yesterday). You will dilute to 100.0 using a 100.0 ml volumetric flask. Googles and gloves here!

Place it into the spectrophotometer and determine its Absorbance.

f) Determine solutions concentration (molarity) using the Beer’s Law graph that was made yesterday (by

using linear algebra).

g) Calculate the moles of copper, grams of copper and finally the percent by mass of copper.

Lab 16 – Non-formal– Write-up requirements: This lab will be an individual Slide-up

1. Title Slide – Title of Lab / name / date

2. Background SLIDE– How spectrophotometry works/Notes

3. Objective SLIDE:

4. DATA SLIDES:

a) Balance reaction between brass (copper only) and nitric acid (HNO₃ ) on Data page

NO₃^-1 —–> NO₂

Cu ——-> Cu⁺²

b) Data table:

a) mass of Brass Shot total

b) balance nitric acid/calculation

c) Serial dilution calculations

c) Beer’s Law Graph on its own SLIDE – I will post digital copies of each lab

d) final calculation of % by mass of copper in shot – Show all calculations

e) Calculate the absorptivity constant (a) using the absorbance (A) and concentrations (c).

A = a b c

Using the absorbance values from the spectrophotometer (A), the path length ( b = 1 cm ), and the

concentrations of these solutions (c) solve for a with the correct units. Make a chart. These

values that you calculate should be similar as it is a constant.

5. Error analysis SLIDE: The limitation of the lab was based on how well you made the solutions and if the absortivity constant STAYED CONTANT! I will explain once you finish step e.

6. Sources Slide: If needed

I will explain e) on Wednesday!

Dissolving of Brass with Nitric Acid: You need to balance this reaction in your lab!

_____________________________________________________

12/20 – Tuesday’s Homework: –

1. Study redox titrations and spectrophotometry labs – Test tomorrow on both labs.

I will focus on Redox Volumetric Titration (Lab 15) and Spectrophotometry (Lab 16). I will not ask specifically about crystal field theory or transitional metals. A great place to study besides your labs is the following worksheet (Stoichiometry 7 – 2010B worksheet) that we had last week. The backside in particular is something that is fair game. I reposted this worksheet and its key from last Wednesday below. Also I reposted its video.

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. Complete Lab 16 on you printed graph! This is the first gift I am giving you! The more you understand this lab the more better you will do tomorrow. DUE Tomorrow!

Here are the new requirements!!

1. Please write the Title of the Lab on the top of the paper.

a) Write the main objective under the Title

2. Please make sure there is a title on your graph.

3. Please include all calculations that lead to the % by mass of copper in the brass including the linear algebra from the Beer’s Law graph.

4. Balance reaction between brass (copper only) and nitric acid (HNO₃ ) on THE BACK!

NO₃^-1 —–> NO₂

Cu ——-> Cu⁺²

5. Please write a comprehensive procedure of the steps of the Lab ON THE BACK!

IF you need help with the calculations or the basic concepts of the lab please use the video posted below:

Lab 16 Review of the calculations:

Stoichoimetry 7 – 2010B 1819.pdf review: The backside in particular.

End of Wednesday.

_________________________________________________________________________. Jump to: Wednesday Homework / top

12/21 – Wednesday – B Day – 2, 3b Lab/4

Main focus –

a) To take the Redox volumetric titration and Spectrophotometry test.

b) To accept many holiday gifts from very appreciative students.

Period 2:

1. Redox volumetric Test

Period 3b/4:

1. Redox volumetric Test

2. Cross Linked Polymer Synthesis activity introduction

______________________________________________

12/21 – Wednesday Homework: –

1. Review your Lab Test on volumetric titrations and Spectrophotometry. I will provide a key or a video.

I will have your graded tests back to you this afternoon!

Volumetric Titrations and Spectrophotometry 1 test key.pdf
View Download

2. Shop and wrap presents for a tall teacher. I am a tall, boys husky.

____________________________________________________________________ Jump to: Thursday Homework / top

12/22 – Thursday – A Day – 2/3a Lab, 4

Main focus –

a) To take the volumetric titration and spectrophotometry test 2.

b) To introduce the synthesize a cross – linked polymer lab for Friday.

Period 2/3a:

1. Test 2 – Volumetric Titrations/Spectrophotometry

2. A = abc , calculate the absorptivity constant for each point, error analysis

Cross linked Polymer introduction –

Period 4:

1. Test 2 – Volumetric Titrations/Spectrophotometry

______________________

The Synthesis of a Cross Linked Polymer

This lab might be a stretch for us right now but I hope it sticks to you.

a) Dissolve 4 grams of polyvinyl chloride in 100 ml of distilled water. Make sure to keep the warm solution at or near 70 degrees Celsius. If too warm it will denature and curl up.

b) In a plastic cup please add 16 ml of sodium tetraborate with your choice of food coloring, glitter, and/or fluorescent compound (if you want to have it glow in the dark).

c) Once the polyvinyl chloride is dissolved, POUR the hot polyvinyl solution into the plastic cup with the sodium tetraborate, food coloring etc and stir with wooden popsicle stick like a banshie!

d) Once the polymer cools enough we will test its physical properties and then dispose of it in a ziplock baggie.

______________________

12/22 – Thursday Homework: –

1. There is no homework tonight except for well YOU KNOW!!!!!! Don’t make me uncomfortable!!

2_______________________________________________________________ Jump to: Friday Homework / top

12/23 – Friday – B Day – 2, 3b Lab/4

Main focus –

a) To bring in heavy presents for your tallest teacher.

b) To synthesize a cross – linked polymer.

Period 2:

1. Cross-Linked Polymer synthesis lab

Period 3b/4:

1. A = abc , calculate the absorptivity constant for each point, error analysis

2. Introduce Cross-Linked polymer Synthesis Lab

3. Cross-Linked Polymer synthesis lab

______________________

12/23 – Holiday Homework: –

1. Please respond to the Holiday Form daily over break by writing the time left in your break with the countdown below everyday.

1: Holiday Form:

Happy New Year!