CHEM140 Lecture Notes - Lecture 2: Dialog Box

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olivelouse517

24 Jan 2016

School

University of Waterloo

Department

Chemistry

Course

CHEM140

Professor

All

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Document Summary

A reference identifies a cell or a group of cells on a worksheet o. References allows you to use data contained in different parts of a worksheet. Tells excel which cells to look in to find values you want to use. Cell references are based on column and row heading. Tells excel how to find another cell starting from the cell containing the. Used if you always want to refer to cells relative to the cell containing formula (c4, f8, etc) the formula, even if you copy or move the formula. Tells excel how to find a cell based on exact location of the cell in the. Used when you want to refer to the same cell regardless of where the o. A formula + will always add values of cells in b1 and b2. whereas worksheet (, , etc) formula is located on the worksheet. B1+b2 will change if it is copied to a different location.

Related Questions

Plastics Identification Data Table
Letter Label	Sampleâs Color	Sampleâs Shape	Floats in Water? (Yes/No)	Sinkersâ Boiling Water Results (Note color/shape changes.)	Sinkersâ Acetone Test Results (Note texture changes.)	Floatersâ Alcohol Test Results (Note number of squirts.)	Plastic Type
A
B
C
D
E
F
G

Questions

Why does PP float before HDPE and LDPE in the alcoholâwater solution?

Did any of the four plastics melt in boiling water? (Hint: How does melting differ from softening in plastics?)

When PS reacts with acetone, is this a physical or chemical change? Explain.

What is the approximate density of the alcoholâwater solution that was diluted with water to help identify LDPE from HDPE?

Looking at plastic containers like milk jugs, deli boxes, detergent bottles, soda bottles, and pill vials makes a person wonder whether they are really all that different from one another. The numbers and letters in the recycle codes seem to indicate that the plastics arenât the same, because these codes all refer to different kinds of plastics. For example, HDPE (high-density polyethylene) has the plastics recycling code number 2, while number 3 is used for PVC or V (polyvinyl chloride). An example of the polyethylene terephthalate (PETE) recycle code is shown at right. In this Activity, you will follow a flowchart to determine the identity of all seven recyclable plastics, without their labels; the first separation involves comparing the densities of plastic pieces to water.

A recycling plant may use manual separation of containers by having people visually recognize and remove containers as they travel along a conveyor belt. All of one kind of plastic will be collected at one location in the plant. Automated sorting may use whole containers or cut-up containers, called flake. Flake sorting involves putting the flakes into large containers of water to separate the âfloatersâ from the âsinkersâ. Whole container sorting uses electromagnetic radiation such as visible, near infrared, and X-ray systems. Optical sorting uses visible light to sort containers by color. Containers exposed to near infrared light absorb specific wavelengths and transmit others based on crystallinity of the plastics. Sensors detect the change in wavelength for each container and initiate the sorting by using jets of air to blast a container to a specific location. X-ray systems detect chlorine atoms in PVC. Recycle plants may sort plastics by using a combination of the systems described above or other technologies that are currently being developed.

Try This

You will need: seven kinds of plastic containers with different recycle codes, scissors, two cups or beakers, two stirring rods or wooden craft sticks, room temperature water, 70% isopropyl alcohol, graduated cylinder, acetone, 2 plastic pipets, hot plate with a 400 mL beaker of boiling water (student groups may share the boiling water), tongs, and forceps.

Cut a small, flat piece (1.5 cm Â´ 1.5 cm) from each container (seven total) and start a data table to record the color and shape of each piece as well as the permanent marker letter label (AâG) your instructor previously marked on each container. If two containers are the same color, cut different shapes (triangle, rectangle, circle, etc.) to help with piece identification. Now you are ready to follow the flowchart. Record your observations in the data table as you go along.

Tap Water Test: Place all seven pieces of plastic in a beaker or cup of room temperature tap water. Stir vigorously with a stirring rod or wooden craft stick to dislodge any bubbles from the plastic pieces. Bubbles tend to adhere to plastics. How would this change the apparent density? Observe and record which pieces sink and which float.

70% Alcohol Test: Remove the pieces that float from the water. Add them to a beaker or cup containing about 20 mL of 70% isopropyl alcohol. Stir. Do the pieces sink or float in the 70% alcohol? How does the density of alcohol compare to water?

Using a plastic pipet, add a squirt of tap water to the beaker containing alcohol. Stir. Do any of the pieces begin to float? When adding water to 70% alcohol, how does the density of the solution change? Keep adding squirts of water and stir until one piece floats. According to the flowchart, what is the identity of this plastic? Remove the piece and record your results.

Add more squirts of water until a second piece floats. Remove the piece and record the identity of the second plastic. You can now identify the third piece since it is still sinking.

Boiling Water Test: Place the four pieces that sank in tap water in the beaker of boiling water for a minimum of 30 s. Using tongs, remove them one at a time and test their flexibility, noting their size and color. Record your results. Which plastics can you now identify using the flowchart?

Acetone Test: Place the final two plastic samples in a small amount of acetone for one minute. Record your results.

Check with your instructor to see whether you correctly identified the seven plastics. You are now ready for an unknown. If your unknown floats in the tap water test, you will need to use the known pieces for PP, HDPE, and LDPE along with your unknown to help you with the identification in the 70% alcohol test.

More Things To Try

You might want to explore plastics coded as 7, âotherâ, or âmixedâ with this approach (see the figure at right). The results may be inconclusive because two or more polymers may be used to make these containers, or it might be 95% of one plastic and 5% another so that it will test as one component. Some containers have many additives to give the container a softer texture; some have several coloring agents. These additives will alter the density of the plastic. Another experiment to try is to test whether black microwavable PET dinner trays react like the transparent PET bottles.

I want to find the Kn value of Cu(II) and EDTA. I was given the formula kn= [ML4]/[ML3][L]. 12.3 ml of edta was used to tritrate 0.1194 grams of Copper in 50 ml of water. The indicator used was murexide.

At the core of general acid-base theories, there is the concept of âtransferâ of one entity to another. In the case of BrÃ¸nsted-Lowry acid base theory, the transferred entity is the proton, and their transfer processes are widely exploited in chemical methods. In addition to proton transfer, electron pairs can also be donated/shared between donors and acceptors. In this case, an atom/molecule, which can accept a pair of electrons, is referred to as a Lewis acid while the entity donating the pair of electrons is referred to as a Lewis base. The most prevalent Lewis acid-base systems involve metal complexes with vacant nd-orbitals, as well as electron deficient systems including B, Si, Ge, etc. The Lewis acid base theory is also known as the Hard-Soft acid base theory (HSABT) with âhardnessâ defined as small highly charged species that are weakly polarizable (Lewis acids). In contrast, âsoftnessâ is described by species that are larger and highly polarizable species with low charge (Lewis bases).
In the case of metal chemistry, Lewis acid-base theory provides a means to describe the ability of âligandsâ to coordinate to metal ions as well as the stability of metal-ligand complexes. Recall that coordination bonds are the donation/acceptance of lone pairs of electrons to empty metal orbitals to another atom; the definition of Lewis acid-base chemistry! The stability of Lewis acid-base complexes can be described through the stability constant which is analogous to the Ka that describes BrÃ¸nsted-Lowry acidities. Many metal ions can coordinate (bind) many Lewis base ligands in a step-wise fashion according to:
M + L = ML K1 = [ML]/[M][L] Eq. 1
ML + L = ML2 K2 = [ML2]/[ML][L] Eq. 2
ML2 + L = ML3 K3 = [ML3]/[ML2][L] Eq. 3
MLn-1 + L = MLn Kn = [ML4]/[ML3][L] Eq. 4
and for which the free energy for this dissociation reaction is given by:
ÎG0 = -RTLnKn Eq. 5.
where R is the gas constant and T is the temperature in Kelvin.
Figure 1: Left- EDTA. Right- Typical EDTA-transition metal complex.
The ethylene diamine tetraacetic acid ligand (EDTA, a Lewis base) provides a mechanism to probe the Lewis acid strength of various metal complexes (Figure 1). This multi-dentate ligand (multiple Lewis base sites on a single ligand) forms complexes with metals of the form:
Mn+ + Y4- = MYn-4 Eq. 6
K = [MYn-4]/[Mn+][Yn-4] Eq. 7
where Y4- is the EDTA ligand.
In this experiment, the Lewis acid strength for two different metals will be examined by measuring the stability constants for the metal-EDTA complex. Of specific interest is the how the Lewis acid strength of the metal ion correlates with:
1) atomic/ionic radii, 2) oxidation state, 3) electron configuration, and 4) polarizability.
You will determine the stability constants of both a Cu2+- and Zn2+-EDTA complexes as well as the corresponding free energy. Using these data, you will compare the relative Lewis acidities of both metals and describe differences in terms of the metal ion properties described above.
.
Chemicals
CuSO4
ZnSO4
EDTA
Murexide
Instruments
Buret
Experimental
You and your group will determine the concentration and ultimately the free energy of Cu(II) and Zn(II) using the hexadentate chelating ligand, EDTA.
You will be given a ~100 mM standardized solution of EDTA (check the label for exact concentration prior to beginning). You will need to weigh ~0.1 g per metal salt sample. Dissolve the metal salt into 50 mL of DI water. Add 2-3 drops of murexide to your metal. After properly preparing your buret with EDTA, titrate your metal with EDTA. Repeat for a total of 3 titrations per metal.
1. Approximately how much EDTA will you need for each titration assuming the metal-saltsâ masses are accurate?
2. What type of indicator is murexide and what color will its endpoint be?
Post-Lab Questions
1.
a) Using the equations given in the introduction and your titration results, what are the Kn of the EDTA-Copper complex? Show calculations.
b) Using the equations given in the introduction and your titration results, what are the Kn of the EDTA-Zinc complex? Show calculations.
2. What are the corresponding ÎG values for the EDTA-metal complexes? Show your calculations
3. Would copper be considered a hard or soft lewis acid? What about zinc? Describe what makes these metals hard or soft.
4. What trends would you predict for EDTA-metal complex Kn and ÎG values when:
a) going down a row of transition metals of the same oxidation state?
b) of the same transition metal with increasing oxidation state? (For example, Iron can exist as Fe(II), Fe(III), Fe(IV), and higher oxidation states)
5. Discussion (formal report style): Compare and contrast the concepts of Lewis and BrÃ¸nsted-Lowry acids and bases. Support these concepts with your data over the last two weeks and with research. Cite your sources.

CHEM140 Lecture Notes - Lecture 2: Dialog Box

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