Electronegativity Essay Example

solution. It isn't table salt, but the salt Ions can carry an electrical charge Just Like salt water can.

The salt In the electrophoresis buffer completes the circuit between the positive and negative electrodes. When the electrodes of the gel box are connected to a power supply, electricity flows through the electrical circuit, causing the negatively charged DNA molecules to move into the agrees gel.

The DNA molecules continue to travel through the agrees toward the positive electrode as long as an electrical current is present. Recall that shorter DNA molecules travel through agrees faster than longer DNA molecules. In this way, agrees gel electrophoresis separates different DNA fragments based on size.

Once the samples are loaded, the electrical current supplied by the power supply not only moves the DNA samples through the gel but the dye molecules as well. Note the colored lines that appear. These lines do not represent the DNA fragments.

These lines represent the dye in the loading buffer that was used to visualize the samples during the loading step. Once the gel run Is complete, the agrees gel can be removed from the gel box and soaked In an tedium bromide solution. Recall that thulium bromide Is the nitrogenous bases in a DNA molecule.

In summary, gel electrophoresis is a vibratory procedure used to separate biological molecules with an electrical current. Together with a gel box and a power supply, an agrees gel can be used to separate DNA molecules based on size. Loading buffer enables scientists to insert DNA samples into the wells of the agrees gel.

Once the electrophoresis procedure is Initiated, the dye in the loading buffer

forms a dye front that is used to determine Nee the procedure is complete. When the electrophoresis procedure is complete, the agrees gel can be soaked in an tedium bromide solution to visualize the DNA bands on a UP box.

Kuris Anthony D. Saucing MILS-la Chromatography Equipments Column Chromatography Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures. The mixture is dissolved in a fluid called the mobile phase, Inch carries it through a structure holding another material called the stationary phase. Column chromatography is basically a type of adsorption chromatography techniques.

Here the separation of components depends upon the extent of adsorption to stationary phase. Here the stationary phase is a solid material packed in a vertical column made of glass or metal.

When a mixture of mobile phase and sample to be separated are introduced from top of the column, the individual components of mixture move with different rates. Those with lower affinity and adsorption to stationary phase move faster and eluted out first while those with greater adsorption affinity move or travel slower and get eluted out last. The solute molecules adsorb to the column in a reversible manner. The rate of the movement of the components is given as follows R= Rate of movement of a component / Rate of movement of mobile phase.

I. E. It is the ratio of distance moved by solute to the assistance moved by solvent.

Planar Chromatography Planar chromatography is a separation technique in which the stationary phase is present as or on a plane. The plane can be a paper, serving as such or impregnated by a

substance as the stationary bed (paper chromatography) or a layer of solid particles spread on a support such as a glass plate (thin layer chromatography).

Different compounds in the sample mixture travel different distances according to how strongly they interact with the stationary phase as compared to the mobile Paper chromatography is a technique that involves placing a small dot or line of ample solution onto a strip of chromatography paper.

The paper is placed in a Jar containing a shallow layer of solvent and sealed. As the solvent rises through the solvent. This paper is made of cellulose, a polar substance, and the compounds Nothing the mixture travel farther if they are non-polar.

More polar substances bond Ninth the cellulose paper more quickly, and therefore do not travel as far. Paper is made of cellulose fibers, and cellulose is a polymer of the simple sugar, glucose. The key point about cellulose is that the polymer chains have -OH groups sticking out all around them.

To that extent, it presents the same sort of surface as silica gel or alumina in thin layer chromatography. It would be tempting to try to explain paper Chromatography in terms of the way that different compounds are adsorbed to different extents on to the paper surface.

In other words, it would be nice to be able to use the same explanation for both thin layer and paper chromatography. Unfortunately, it is more complicated than that! The complication arises because the cellulose fibers attract water vapor from the atmosphere as well as any water that Nas present when the paper was made.

You can therefore think of paper as being

cellulose fibers with a very thin layer of water molecules bound to the surface. It is the interaction with this water which is the most important effect during paper chromatography. Electrochemical Cell Set-up(experiment) a) The simplest experimental set up for performing electrochemical experiments.

B) A schematic representation of a three electrode potential . Up to now we discussed shortly the principles of semiconductor-electrolyte interfaces. However, it was said nothing about the practical implementation of electrochemical techniques.

Let us start by discussing the most simple experimental setup for performing electrochemical measurements. The following elements are necessary: three electrodes immersed into an electrolyte; A battery; A voltmeter.

An imperative. Ere electrode, which has to be studied or where the electrochemical reaction should take place (in our case it will be the electrode in which we intend to introduce pores), is called the working electrode (WE). The second electrode, which is closing the circuit, is called the counter electrode (CE).

The third one, used to measure the Olathe between the electrolyte and WE, is called the reference electrode (RE).

If a current is flowing thought a solid-electrolyte interface, chemical reactions will occur at the interface. Electrons leaving the solid will reduce species in solution, whereas electrons moving into the solid lead to the oxidation of species in solution. Due to the Chemical reactions at the interface the composition of the electrolyte near the surface of the solid will change continuously and thus the distribution of the voltage across the semiconductor-electrolyte interface will vary as well.

This is especially true at high current densities.

For this reason, in order to maintain a constant composition of the solution near the

surface of the sample, I. E. The working electrode, continuous a) A schematic representation of a setup with a three electrode potential. B) A schematic representation of a set up with a four electrode potential.

As long as the contact between the sample and the working electrode is good enough. However, if the mimic resistance between the WE and the sample is not sufficiently small, e. G. "hen using In/Ga alloy, a four electrode potential must be used.

The fourth electrode is called the sense electrode (SE ) and is connected to the sample. Now, the potential can be regarded as being composed of two 'independent' subsystems. One containing the WE and CE electrodes through which the current is flowing. Correspondingly, the second subsystem contains SE and RE electrodes and measures the potential.

A feedback interaction between the two subsystems results in an ideal tool for controlling electrochemical processes. In this configuration the contact between the sense electrode and the sample is not critical because no current is lowing through it.

Now the desired potential will be exactly applied on the sample/ electrolyte Junction. In spite of the fact that a four electrode potential diminishes the importance of the contact quality between WE and the sample, during the pore formation process the quality of the contact between the sample and the working electrode is still very important.

It determines how uniform the current is distributed across the whole surface of the sample. If the contact is not uniform the distribution of the current and consequently the porous layer will not be uniform as well.

A significant improvement of the uniformity of the backside contact can

be achieved by liquid contact, I. E. The sample has two electrolyte Junctions. The first Junction (the front side) will be the one of interest and where the pores will grow.

The second ;unction will play the role of an uniform backside contact. On both Junctions electrochemical reactions will take place. If at the front Junction an anodic reaction takes place, then at the back contact a catholic reaction will occur. This idea can be realized by the so called double electrochemical cell.

Separation of Actions and Anions Classification of the Actions and Anions Ere five groups of actions and the characteristics of these groups are as follows: *Group 1 Actions of this group form precipitates with dilute hydrochloric acid. Ions of this group are lead(al), mercury(l), and silver(l). *Group 2 The actions of this group do not react with hydrochloric acid, but form precipitates with hydrogen sulfide in dilute mineral acid medium. Ions of this group are bismuth(all), cadmium (II), tin(al), tin(lb), arsenic(all), arsenic(V), antimony(all), and antimony(V).

He first four form the sub-group 2/a and the last six the sub-group bib. Nile sulfides of actions in Group 2/a are insoluble in ammonium polypeptide, those of actions in Group bib are soluble. *Group 3 Actions of this group do not react either with dilute hydrochloric acid, or with hydrogen in dilute mineral acid medium. However they form precipitates with ammonium sulfide Cross, Abaca (s)in neutral or monomaniacal medium. Actions of this group are iron(al), aluminum(all), and zinc(al). *Group 4 Actions of this group do not react with the reagents of Groups 1, 2, and 3.

They form precipitates with ammonium carbonate in the presence of

ammonium chloride in neutral medium. Actions of this group are calcium(al), strontium(al), and barium(al). *Group 5 Common actions, which do not react with reagents of the previous groups, form the last group of actions, which includes magnesium(al), lithium(l), sodium(l), potassium(l), and ammonium(l) ions. Ere methods available for the detection of anions are not as systematic as those Inch have been described above for actions.

No really satisfactory scheme has yet been proposed which permits the separation of the common anions into major groups, and the subsequent unequivocal separation of each group into its Independent constituents; however, it is possible to detect anions individually in most cases, after perhaps a 1-2 stage separation. It is advantageous to remove all heavy metals from the sample by extracting the anions through boiling with sodium carbonate solution; heavy metal ions are precipitated out in the form of carbonates, Nile the anions remain in solution accompanied by sodium ions.

He following scheme of classification of anions has been found to work well in practice; anions are divided into four groups on the basis of their reactions with elute hydrochloric acid and of the differences of solubility's of their barium and silver salts. Group 1 Visible change, gas evolution and/or formation of a precipitate, with dilute hydrochloric acid. Ions of this group are carbonate, silicate, sulfide, culprits, and theosophical. Group 2 The anions of this group do not react with hydrochloric acid, but form precipitates with barium ions in neutral medium.

Ions of this group are sulfate, phosphate, fluoride, and borate. Group 3 Anions of this group do not react either with dilute hydrochloric acid, or with barium ions in neutral

medium.

However, they form precipitates with silver ions in dilute nitric acid medium. Anions of this group are chloride, bromide, iodide, and technicians. Group 4 Common anions, which do not react with reagents of the previous groups, form the last group of anions, which includes nitrite, nitrate and chlorate ions. He identification of a single action in solution is a fairly simple and straightforward process, although without a good identification scheme it may require so many experiments as the number of potential actions, if we know at least one specific reaction for each action.

In order to reduce the number of tests required for the Identification, it is important to develop a good identification scheme, which reduces the number of potential actions step by step placing them into groups. There are several possibilities and anyone could develop his/her own identification scheme. He scheme you find below follows the classification of actions into groups, as described in the Freshness' system. In case of a solid sample it is assumed that the sample is soluble in water or dilute nitric acid. Once the action is found, its presence should be verified by other, characteristic sections. Resting FOR A SINGLE ACTION IN SOLUTION 11) Group I actions Add to the solution an excess of dilute HCI.

If there is no change, follow (AAA). A Unite precipitate may contain Pub+, High+ or Gag+. Filter and wash the precipitate and then add NH solution to the precipitate.

If the precipitate does not change:Pub+ present turns black: High+ present dissolves:Gag+ present AZ) Group 'IA actions Acidify the solution and add HAS in excess. If there is no change follow (3).

A

precipitate may result if Hug+, Bib+, cue+, CDC+, ASS+, ASS+, Sob+, Sob+, sin+, sin+ Nerve originally present. Check the color of the precipitate ! ) Filter the precipitate, Nash with dilute HCI, and treat with an excess of (NH)ass. If the precipitate dissolves, follow (b). Yellow: CDC+ present rake a fresh sample and add dilute Noah.

If the precipitate is yellow:Hug+ present white:Bib+ present b) Group BIB actions blue:Cue+ present Add dilute HCI to the (NH)ass filtrate in excess, when the precipitate reappears.

Rake a fresh sample, acidify, and precipitate the sulfide. Examine its color: brown precipitate:Sin+ present An orange precipitate indicates Sob. To identify its oxidation state, take a fresh sample, acidify with 1:1 HCI and add SKI: no coloration:Sob+ present brown collaborations+ present A yellow precipitate indicates As or Sin+.

Add (NH)CHIC in excess. If the precipitate remains undisclosed:Sin+ present Perform the luminescence test for identifying Sin+ ions. If the precipitate dissolves:Ass+ or Ass+ present.

Or identify the oxidation state of As present in the solution, take a fresh sample, no coloration:Ass+ present brown coloration:Ass+ present 13) Group Ill actions Neutralist the solution with NH solution and add (NH)AS in excess. If there is no change, follow (4). Examine the precipitate. A green precipitate indicates Car+.

Too fresh sample, add Noah: green precipitate which dissolves in an excess of the reagent:Car+ present A pink (flesh-like) precipitate indicates Man+. To a fresh sample, add Noah: precipitate, which turns darker on standing:Man+ present white A white precipitate may be caused by AAA+ or Zen+.

Too fresh sample add NH, first n moderate amounts, then in excess: white precipitate, which dissolves in excess NH solo. :

Zen+ present white precipitate, which remains unchanged if excess NH is added: AAA+ present A black precipitate occurs if CO+, Inn+, Fee+ or Fee+ were present originally.

Filter, wash and mix the precipitate with 1:1 HCI. Ere precipitate dissolves if Fee+ or Fee+ were present, otherwise it remains unchanged. Green precipitate, turning dark on standing: dark brown precipitate: blue precipitate, turning pink if excess Noah is added: green precipitate, which remains unchanged on standing: Fee+ present Fee+ present CO+ present Inn+ present 14) Group IV actions To the solution add (NH)CHIC in excess, in the presence of Enoch.

If there is no precipitation, follow (5). A white precipitate indicates the presence of ABA+, Sir+ or Ca+.

To a fresh sample ad a four fold (in volume) of saturated Cases solution: immediate white precipitate:ABA+ present a white precipitate is slowly formed: Sir+ present no precipitation occurs:Ca+ present 15) Group V actions Heat a fresh sample gently with some dilute Noah: characteristic dour of ammonia: NH+ present Carry out a flame test with the original sample: red coloration: yellow coloration: pale violet coloration: Or the solution add Noah in excess: white precipitate, which turns red by adding a few drops of titan yellow reagent:MGM+ present Lie present An+ present K+ present Resting FOR A SINGLE ANION IN SOLUTION

The identification of a single anion in solution is a fairly simple and straightforward process, and anyone could develop his/her own identification scheme. The scheme below follows the classification of anions into four groups, as solution. In case of a solid sample it is assumed that the sample is soluble in water. Once the anion is found, its presence

should be verified by other, characteristic 11) Group I anions Add to the solution an excess of dilute HCI.

If there is no change, follow (2). If a Unite precipitate or/and gas liberation is observed, one of the following anions 2-2- 2-2-2- ay present: CO , Isis , S , ASS , SASS . Unite, gelatinous precipitate without the liberation of any gas: Isis present Unite precipitate with the liberation of ASS. The gas is tested with a filter paper moistened with potassium iodated and starch solution. 2- blue coloration:SASS present No precipitate, only gas liberation is observed.

Test the gas with filter paper moistened with lead acetate solution. Black coloration:S present Test the gas with filter paper moistened with potassium iodated and starch solution. Blue coloration:ASS present Introduce the gas into bratty or lime water: white precipitate:CO present Z) Group II anions Neutralist the solution and add Abaca solution. If there is no change follow 3). 2-3- -3- A white precipitate may result if ASS , POP , F , or 803 was originally present.

Filter the precipitate, and add HCI solution. Recipient is not soluble: Add concentrated sulfuric acid to the precipitate or to the original solid sample, and warm the test tube: test-tube acquires a greasy appearance:F present ASS present Add concentrated sulfuric acid and ethanol to the precipitate or to the original 3- green-edged flame:BIB present rake a fresh sample and add ammonium moldboard reagent. Allow, crystalline precipitate:POP present 13) Group Ill anions Acidify the solution with dilute nitric acid and add Again solution. If there is no change, follow Examine the precipitate.