Triboelectric Series Become positive in charge The following - - PDF document

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http://www.school-for-champions.com/science/static_materials.htm

Become positive in charge

The following materials will tend to give up electrons when brought in contact with

• ther materials. They are listed from those with the greatest tendency to give

electrons to those that barely give up electrons. Dry human skin Greatest tendency to giving up electrons and becoming highly positive (+) in charge Leather Rabbit fur Fur is often used to create static electricity Glass The glass on your TV screen gets charged and collects dust Human hair "Flyaway hair" is a good example of having a moderate positive (+) charge Nylon Wool Lead A surprise that lead would collect as much static electricity as cat fur Cat fur Silk Aluminum Gives up some electrons Paper

Neutral

There are very few materials that do not tend to readily attract or give up electrons when brought in contact or rubbed with other materials. Cotton Best for non-static clothes Steel Not useful for static electricity

Become negative in charge

The following materials will tend to attract electrons when brought in contact with

• ther materials. They are listed from those with the least tendency to attract

electrons to those that readily attract electrons. Wood Attracts some electrons, but is almost neutral Amber Hard rubber Some combs are made of hard rubber Nickel, Copper Copper brushes used in Wimshurst electrostatic generator Brass, Silver Gold, Platinum It is surprising that these metals attract electrons almost as much as polyester Polyester Clothes have static cling Styrene (Styrofoam) Packing material seems to stick to everything Saran Wrap You can see how Saran Wrap will stick to things Polyurethane Polyethylene (like Scotch Tape) Pull Scotch Tape off surface and it will become charged Polypropylene Vinyl (PVC) Many electrons will collect on PVC surface Silicon Teflon Greatest tendency of gathering electrons on its surface and becoming highly negative (-) in charge

Triboelectric Series

2 An effort to reconstruct Millikan's "exemplary" experimental thinking revealed serious discrepancies between Millikan's notebooks and his published "raw" data (Holton, 1978). The numerous notes which are scattered across the pages cast further doubt on Millikan's integrity: This is almost exactly right & the best one I ever had!!! [20 December 1911] Exactly right [3 February 1912] Publish this Beautiful one [24 February 1912] Publish this surely / Beautiful !! [15 March 1912, #1] Error high will not use [15 March 1912, #2] Perfect Publish [11 April 1912] Won't work [16 April 1912, #2] Too high by 1½% [16 April 1912, #3] The notebooks reveal that, indeed, substantial data are missing from Millikan's published reports. Of 175 total drops documented in the notebooks, only 58 (barely one-third) appear in the final paper. By contrast, Millikan had announced in his 1913 paper that "It is to be remarked, too, that this is not a selected group of drops but represents all of the drops experimented on during 60 consecutive days, during which time the apparatus was taken down several times and set up anew" [his own emphasis!]. In his 1917 book, The Electron, he repeats this statement and then adds, "These drops represent all of those studied for 60 consecutive days, no single drop being omitted." http://www1.umn.edu/ships/ethics/millikan.htm

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Was Millikan unethical?

At first blush, this outrageous violation of scientific integrity would seem to discredit Millikan's findings. Even if one assumes that standards of reporting data earlier in the century were less rigorous, Millikan clearly misrepresented the extent of his data. One may caution students, however, that we may not want to conclude that therefore there was no good, "scientific" basis for his selective use of data. A more complete analysis of Millikan's notebooks, in fact, and of the nature of the experimental task that they crudely document, reveals more tellingly the reasons that Millikan included some drops and excluded others. http://www1.umn.edu/ships/ethics/millikan.htm

4 One may examine further specifically when the observations that Millikan excluded occurred. The first 68 observations, for instance, were omitted entirely. Why? Following February 13, 1912 (which marks the first published data), one may also note, the number of excluded results decreases as the series of experiments proceeds. Apparently, Millikan became more skilled as time went on at producing stable, reproducible data. Prior to February 13th, one may infer, he was still working the "bugs" out of the apparatus and gaining confidence in how to produce trustworthy results. That is, he was testing his equipment, not any theory of the electron or its charge. Here, the notebooks help focus our attention on the apparatus and the material conditions for producing evidence, not the role of the evidence itself. http://www1.umn.edu/ships/ethics/millikan.htm In fact, Franklin notes, Millikan threw out data that was "favorable" as well as "unfavorable" to his expectations. Clearly, Millikan's results were over-determined. That is, he had more data than he needed to be confident about his value for the electron's charge. Here, the redundancy of data was an implicit method for safeguarding against

• error. Thus, what appears as fraud from one perspective becomes,

from an experimental perspective, a pattern of good technique. http://www1.umn.edu/ships/ethics/millikan.htm

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There are rules for dealing with “bad” data:

• 1. Use median instead of mean for

small sample sizes.

• 2. Acquire more data ($$).
• 3. Q test or Grubbs test to identify outliers

(careful!).

• 4. Report the procedure used to deal with

error.

https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spect rpy/nmr/nmr1.htm

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https://www.math10.com/en/algebra/probabilities/binomial- theorem/binomial-theorem.html

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https://wonderopolis.org/wonder/what-is-pascals-triangle

5000 10000 15000 20000 25000 30000 35000 40000 45000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

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5000 10000 15000 20000 25000 30000 35000 40000 45000 1 2 3 4 5 6 7 8 9 1011121314151617

Defining a new dependent coordinate (z) in terms of x, the mean, and the standard deviation and plotting y versus z gives the graph on the right.

(p. 70, Harris 8e)

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https://www.chemistry.mcmaster.ca/esam/Chapter_3/section_2.html

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N = number of measurements s = standard deviation s = population standard deviation

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Three common cases for using the t test to compare measured values:

• 1. the mean of one sample is compared to a “known” value
• r established standard

Example: molarity “known” to be 0.1147 M

• 2. the mean of one sample is compared to the mean of

another sample

Examples: concentration of phenol in Hogtown Creek; average height of CHM 3120 students

• 3. comparing individual data points in a set of paired

measurements; this approach is commonly used to compare different analytical techniques (p. 78, Harris 8e)

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Three common cases for using the t test to compare measured values:

• 1. the mean of one sample is compared to a “known” value
• r established standard

Example: molarity “known” to be 0.1147 M

• 2. the mean of one sample is compared to the mean of

another sample

Examples: concentration of phenol in Hogtown Creek; average height of CHM 3120 students

• 3. comparing individual data points in a set of paired

measurements; this approach is commonly used to compare different analytical techniques (p. 78, Harris 8e)

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What is the pH of 1  108 M HNO3(aq)?

• A. 6.0
• B. 7.0
• C. 8.0
• D. 9.0

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Rank the following solutions in order of increasing pH: 0.1 M HNO2, 0.1 M HNO3, 0.1 M NaNO2, 0.1 M NaNO3, 0.1 M NaOH

• A. HNO2 < HNO3 < NaNO2 < NaNO3 < NaOH
• B. HNO3 < HNO2 < NaNO2 < NaNO3 < NaOH
• C. HNO2 < HNO3 < NaNO3 < NaNO2 < NaOH
• D. HNO3 < HNO2 < NaNO3 < NaNO2 < NaOH
• E. HNO3 < HNO2 < NaOH < NaNO3 < NaNO2

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2 4 6 8 10 12 14 10 20 30 40 50 60 70 80 90 100

pH Volume of 0.10 M NaOH added (mL) HCl HNO2

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Which acid / conjugate base pair would be best to prepare a 6.85 pH buffer? Three practical methods to prepare a buffer:

1- First Method : By the Titration, in the presence of one of the two buffer forms with strong base or acid:

 Prepare a buffer composed of an acid and its salt by adding a

strong base(e.g. NaOH) to a weak acid (e.g. Acetic acid) until the required pH is obtained

 If the other form of buffer is available (in this case sodium

acetate), a strong acid is added (e.g. HCl) until the required pH is

• btained.

CH3COONa+HClCH3COOH+NaCl

 So acetate buffer is formed(CH3COOH/CH3COONa)

Source: fac.ksu.edu.sa/sites/default/files/BUFFER_0.ppt

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

Advantages: Easy to understand. Useful when only one form of the buffer is available (in this case acetic acid)



Disadvantages:

1.

Slow.

2.

May require lots of base (or acid). 2- Second Method: Using the buffer pKa , calculate the

amounts (in moles) of acid/salt or base/salt present in the buffer at the desired pH.

 If both forms (i.e., the acid and the salt) are available, convert the

amount required from moles to grams ,using the molecular weight of that component, and then weigh out the correct amounts of both forms. Or convert moles to volume if the stock is available in the liquid form.

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

Advantages:

1.

Fast.

2.

Easy to prepare.

3.

Additional pH adjustment is rarely necessary, and when necessary, the adjustment is small.



Disadvantages:

1.

Requires the buffer pKa

2.

and solving two equations.

.3-The Thired Method: Using table

 Find a table of the correct amounts of acid/salt or

base/salt required for different pH's

 Dissolve the components in slightly less water than is

required for the final solution volume.

 Check that the pH and correct if necessary.  Add water to the final volume.

21 

Advantages:

1.

Easy to do (with appropriate table).

2.

Convenient for frequently prepared buffers.



Disadvantages:

1.

May be impossible to find table.

2.

Table may be incorrect.

3.

Requires both forms of buffer.

4.

Component amounts from table will need to be adjusted to give the buffer concentration and volume in your solution.