Inorganic Chemistry Practical by Dr Deepak Pant (the reading strategies book txt) 📖

when you are through with it. Weigh carefully about 0.9 g of EDTA (record to the nearest 0.1 mg). Quantitatively transfer this into a 250 mL volumetric flask then add 2-3 mL
of pH 10 ammonia buffer. Fill the flask about halfway to the mark with deionized water and swirl to dissolve. This process can take up to 15 minutes. Once dissolved, dilute to the mark and then cap and invert the flask at least 6 times to get a uniform solution. Keep the solution capped.
The Blank and Titration Procedure.
In order to correct for any error attributable to the deionized water and the indicator color transition, you will be analyzing a blank solution. The volume of EDTA used to titrate the blank will be subtracted from all other titration volumes.
Pipette a 10.00 mL sample of deionized water into a clean 250 mL Erlenmeyer flask. Add about 1mL of ammonia buffer, using a 10mL graduated cylinder. At this point heat the flask on the hot plate until condensation forms on the inside rim of the flask. Immediately add a few drops of indicator. If the solution turns blue, there is no measurable calcium or magnesium in solution and you will not have a blank correction. If the solution stays red or violet, immediately start titrating with the EDTA solution. Titrate until there is no trace of red or violet in your solution.
Be sure to go dropwise as you approach the endpoint. The kinetics of the indicator reaction is low; heating aids in speeding up the transition from red to blue. However, it is necessary to titrate slowly as you approach the endpoint so that it is not overshot.
The color change upon reaching the endpoint for this titration is subtle. Two pieces of advice will help improve your results. First, ask a TA or the instructor to inspect your solution near the endpoint of your first titration to be sure you really are at the endpoint. Second, try to reach the same color for each titration of your unknowns and standards. This consistency in technique will improve the precision of your measurements.

Titrating the Unknown.
Repeat the above procedure, substituting 10.00 mL portions of your unknown sample, in place of the 10.00 mL deionized water sample. Repeat the unknown titration between 3 and 6 times depending upon time constraints. Typically, the more titrations you perform, the better the results.


Chromatography
Chromatography is a family of analytical chemistry techniques for the separation of mixtures. It involves passing the sample, a mixture which contains the analytic, in the "mobile phase", often in a stream of solvent, through the "stationary phase." The stationary phase retards the passage of the components of the sample. When components pass through the system at different rates they become separated in time, like runners in a marathon. Ideally, each component has a characteristic time of passage through the system. This is called its "retention time."
A chromatograph takes a chemical mixture carried by liquid or gas and separates it into its component parts as a result of differential distributions of the solutes as they flow around or over a stationary liquid or solid phase. Various techniques for the separation of complex mixtures rely on the differential affinities of substances for a gas or liquid mobile medium and for a stationary adsorbing medium through which they pass; such as paper, gelatin, or magnesium silicate gel.
Analytical chromatography is used to determine the identity and concentration of molecules in a mixture. Preparative chromatography is used to purify larger quantities of a molecular species. Most of the following refers to analytical chromatography.
Chromatography theory
Chromatography is a separation method that exploits the differences in partitioning behavior between a mobile phase and a stationary phase to separate the components in a mixture. Components of a mixture may be interacting with the stationary phase based on charge, relative solubility or adsorption. There are two theories of chromatography, the plate and rate theories.
Retention
The retention is a measure of the speed at which a substance moves in a chromatographic system. In continuous development systems like HPLC or GC, where the compounds are eluted with the eluent, the retention is usually measured as the retention time Rt or tR, the time between injection and detection. In interrupted development systems like TLC the retention is measured as the retention factor Rf, the run length of the compound divided by the run length of the eluent front:

The retention of a compound often differs considerably between experiments and laboratories due to variations of the eluent, the stationary phase, temperature, and the setup. It is therefore important to compare the retention of the test compound to that of one or more standard compounds under absolutely identical conditions.
Paper chromatography
A small spot of solution containing the sample is applied to a strip of chromatography paper about one centimetre from the base. This sample is adsorbed onto the paper. This means that the sample will contact the paper and may form interactions with it. Any substance that will react with (and thus bond to) the paper cannot be measured using this technique. The paper is then dipped in to a suitable solvent (such as ethanol or water) and placed in a sealed container. As the solvent rises through the paper it meets the sample mixture which starts to travel up the paper with the solvent. Different compounds in the sample mixture travel different distances according to how strongly they interact with the paper. Paper chromatography takes some time and the experiment is usually left to complete for some hours.
The final chromatogram can be compared with other known mixture chromatograms to identify sample mixes. Two-way paper chromatography involves using two solvents and rotating the paper 90o inbetween. This is useful for separating complex mixtures of similar compounds.


Thin layer chromatography (TLC)
In thin layer chromatography or TLC the stationary phase consists of a thin layer of adsorbent like silica gel, alumina, or cellulose on a flat carrier like a glass plate, a thick aluminum foil, or a plastic sheet.
The process is similar to paper chromatography with the advantage of faster runs, better separations, and the choice between different adsorbents. TLC is a standard laboratory method in organic chemistry. Because of its simplicity and speed TLC is often used for monitoring chemical reactions and for the qualitative analysis of reaction products.
TLC plates are made by mixing the adsorbent with a small amount of inert binder like calcium sulfate (gypsum) and water, spreading the a thick slurry on the carrier, drying the plate, and activation of the adsorbent by heating in an oven. The thickness of the adsorbent layer is typically around 0.1 - 0.25 mm for analytical purposes and around 1 - 2 mm for preparative TLC.
Several methods exists to make colorless spots visible:
• Often a small amount of a fluorescent dye is added to the adsorbent that allows the visualization of UV absorbing spots under a black light ("UV254").
• Iodine vapors are a general unspecific color reagent.
• Specific color reagents exist into which the TLC plate is dipped or which are sprayed onto the plate.
Once visible, the spots can be quantified by way of calculating their Rf values. These values should be the same regardless of the extent of travel of the solvent, and in theory are independant of a single experimental run. They do depend on the solvent used, and the type of TLC plate.


Thin-Layer Chromatography: Analysis of a Commercial Analgesic
Most non-prescription pain-relieving remedies contain aspirin (o-acetylsalicylic acid) or acetaminophen - and some contain both. Many also have some auxiliary compounds with analgesic properties. In addition, caffeine is included in some preparations. Caffeine is not an analgesic, but aids in the relief of certain types of headaches because of its stimulant effect (CNS and cardiac).
PROCEDURE
Crush the tablet to a powder on a piece of glassine weighing paper. Put half of the powder in a 5 mL plastic beaker and add 2 mL of methanol and 1 mL of dichloromethane.
Stir the mixture with a glass rod for about one minute to allow the solvent to extract the active ingredients. Allow the insoluble matter to settle. Carefully decant the supernatant liquid into a clean, dry 5-mL beaker.
On a TLC strip coated with Silica Gel IB-F, apply a spot of the solution of "unknown" and two of the four known solutions. On a second Silica Gel strip, spot the "unknown" solution and the remaining two known solutions. Be sure to mark the identity of each spot on each strip. Develop each chromatogram in a bottle containing 100% ethyl acetate.
Examine each strip under the ultraviolet light viewer (short wave UV light). Compare the spot positions (the Rf values) of the constituents of the tablet with those of the individual authentic substances. If very little movement of components has occurred on a strip, do not mark any visible spots with a pencil. Replace the strip in the bottle and repeat the development. Make a table recording the distance each substance moved from the origin and the distance the solvent moved.


Lab Report
Title: Thin Layer Chromatography
Name:
Date:
In the following table, enter the distance traveled by each spot, along with its' corresponding Rf

Sample Distance Front
Traveled (cm). Distance Component
Traveled ( cm.) Silica Gel TLC Plate in
100 % Ethyl Acetate Solvent

Aspirin
RfAspirin = __________

Acetaminophen
RfAcetominophen = __________

Caffeine
RfCaffeine = __________

Phenacetin
RfPhenacetin = __________


Unknown
Tablet

1_________

2_________

3_________

4_________
Rf1 = __________

Rf2 = __________

Rf3 = __________

Rf4 = __________
Experiment: Paper Chromatographic separation of Ag(I),Hg2(II) and Pb (II) Ions
Materials required
The following materials are required for the separation of Ag(I) ,Hg(II) and Pb(II) ions
(a) CHROMATOGRAPHY PAPER: What man no.1 filter paper strip of 25cm x 7cm used.
(b) JAR: Paper chromatographic jar is used whose height is 30 cm and diameter 10cm.
(c) Salt solution: aqueous 1% solution of silver nitrate , mercurous nitrate and lend nitrate are prepared .these solution are slightly acidified with dilute nitric acid .
(d) Developing solvents: one can use anyone of the following solvents:
(i) Tertiary butanol (40 ml) + acetone (30 ml)+water (12 ml)+conc.nitric acid (8ml)
(ii) Methyl n-propyl keton (85ml)+10 N HCI (15 ml)
(iii) n – butyl alcohol mixed with 5% (V/V) of glacial acetic acid followed by water to turbidity
(iv) Distilled or deionised water.
(e) Visualising agent :one may use anyone of the following visualising agents
(i) Colourless ammonium sulphide solution is prepared by bubbling H2S in dilute NH4OH.