Chemical Tests
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Mix 1 – 2 cm3 of A with about 5 cm3 of tap water. Test the pH of the mixture with a few drops of Universal Indicator. Record your observation(s) and conclusion.
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In the fume cupboard, add a small spatula measure of solid PCl5 to 1 – 2 cm3 of A. Test any gas evolved with the stopper from a concentrated ammonia bottle. Record your observation(s) and conclusion.
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Warm about 1 cm3 of A with 2 cm3 of an equal mixture of potassium dichromate and 2M sulphuric acid in a boiling tube. Note any colour change and write an equation to represent the reaction occurring.
Chemical Tests Observations
- After mixing, there were two layers in the test tube the bottom layer was a white (cloudy) precipitate and the top layer was a clear liquid. After adding the Universal Indicator it remained green.
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After adding PCl5 to the test tube there was a sudden reaction and a gas was given off. Testing it with the stopper from the concentrated ammonia bottle gave white fumes.
- In the beginning the mixture of the compound A, potassium dichromate and 2M sulphuric acid was pale yellowish/green. After heating the mixture in a boiling tube the mixture turned to pale blue color.
Chemical Tests Results
- The green color of the universal indicator after being added proved that the compound was neutral pH.
- The white fumes given off after testing the gas with the stopper from the concentrated ammonia bottle told us that the gas given off was HCL and this proved that there was an OH group of an alcohol in the compound.
- The color changing of the solution from pale yellowish/green to pale blue tells us that the alcohol has been oxidized to ketone.
Identity And Structure
The unknown compound A is likely to be Propan–2-ol.
Structure:
H H H
H C C C H
H OH H
Compound B
Composition: C = 73.0%
H = 5.4% hence E.F. = C9H8O2
O = 21.6%
Compound B is AROMATIC with one side chain and two functional groups. The Mr is 148.
If the Mr is 148, hence the Molecular Formula: C9H8O2
The following chemical tests will further identify the compound.
Chemical Tests
- Warm a spatula measure of B with sodium carbonate solution and suggest the identity of the gas evolved.
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In a DRY test tube add a spatula measure of PCl5 to a similar amount of solid B. Warm gently if required and test the gas evolved with the stopper from a bottle of concentrated ammonia solution.
- Prepare a HOT aqueous solution/suspension of B in a boiling tube and divide into four portions in order to carry out the following tests:
- Add a few drops of litmus solution
- Add magnesium ribbon and reheat. Identify the gas.
- Add a few drops of bromine water and shake.
- Add a few drops of acidified potassium manganate (VII).
From the results of these tests identify the TWO functional groups present in B and draw a possible structural formula.
Predict the structures of the products formed when B reacts separately with (a) ethanol + concentrated H2SO4 (b) bromine liquid.
25 cm3 of a solution of Compound B required 15.2 cm3 of 0.05M NaOH for neutralisation. Calculate the molarity and mass concentration of the solution of B.
Chemical Tests Observations
- After warming the spatula measure of the compound b with the sodium carbonate a gas was given off.
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After adding PCl5 to the boiling tube and warming it there was a sudden reaction and a gas was given off. The test tube got a layer of burned black substance on its outside. Testing the gas with the stopper from the concentrated ammonia bottle gave white fumes.
- a) After adding the lithmus solution the suspension went red
b) Adding the magnesium and reheating results in a reaction and a gas is given off.
c) The yellow/orange color of bromine water goes transparent meaning it decolorized.
d) The acidified potassium manganate decolorized as well.
Chemical Tests Results
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The colorless gas that was given off was diagnosed as CO2. This was the, prove for the presence of a carboxylic acid functional group.
- The white fumes given off after testing the gas with the stopper from the concentrated ammonia bottle told us that the gas given off was HCL and this proved that there was an OH group of a carboxylic acid in the compound.
- a) The solution to change the color to red meant that the compound is acidic.
b) The gas that was given off was hydrogen.
c) The decolorizing of the Bromine Water meant that there was an Alkene functional group in the compound.
d) The decolorizing of the acidified potassium manganate is prove that there is an acid group in the compound.
Identity And Structure
The unknown compound B is likely to be Cinnamic Acid.
Structure:
Compound C
Composition: C = 66.6%
H = 11.2% hence E.F. = C4H8O
O = 22.2%
The mass and infra red spectra of compound C was given can be found on the Appendix sheet. The Mr and the molecular formula of C were deduced. The infra red spectrum gave a signal and was identified as:
Mr of C = 72 M.F. = C4H8O
1720cm-1 to 1750cm-1 = C = O stretch in Aldehyde.
Chemical Tests
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Half fill a test tube with Tollen’s reagent (a solution of Ag2O in dilute ammonia) then add 10 drops of C. Stand in a hot water bath for a few minutes.
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To about 2 cm3 of C in a boiling tube add about 5 cm3 of Fehling’s solution then heat carefully with a Bunsen burner.
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Mix 2 cm3 of C with a few cm3 of acidified potassium dichromate in a boiling tube. Heat the mixture until it just boils and account for any colour change.
What can you conclude about the functional group in C from the results of tests 1 and 2? Give the name and structural formula of Compound C. In each of the three tests above, C is converted into the same end product – draw the structure of this product.
Chemical Tests Observations
- After adding the 10 drops of compound C in the Tollen’s reagent present in the test tube and letting the test tube stand in a hot ice bath there was a silver mirror on the inside surface of the test tube.
- In the beginning the solution was blue, after heating it the Bunsen burner the solution changed color to deep Brown/Red precipitate.
- The color of the solution to start with was Orange but after heating it changed color to pale Green.
Chemical Tests Results
- The silver mirror that appeared on the inside surface of the test tube proved that the compound initially was an Aldehyde.
- The changing of the color of the solution from Deep Blue to Brick Red was another prove that the compound initially was an Aldehyde.
- The changing of the color of the solution from orange to pale green shows the oxidation of the Aldehyde.
Identity And Structure
The unknown compound C is likely to be Butanal.
Structure:
Compound D
Composition: C = 20.0%
H = 6.7% hence E.F. = CH4N2O
O = 26.7%
N = 46.6%
D is a natural compound formed as a product of the metabolism of proteins. A normal individual roughly excretes between 28 and 30g of D per day.
The following information was given to help find the Mr and MF of D.
Compound D can be completely hydrolysed in the presence of a suitable enzyme. One mole of water will hydrolyse one mole of D. 250 cm3 of a solution of D containing 120 gdm-3 required 9 cm3 of water for complete hydrolysis.
Working:
D + H20 Hydrolysed Products
250cm-1 9cm-1
120 g/dm3 9 g
; 30 g ; 0.5 Mole
Hence 0.5 Mole Of D is reacting = 30 g
So 1 Mole = 60 g
Mr of D = 60 M.F. = CH4N2O
Chemical Tests
- Dissolve a spatula measure of D in tap water and add an equal volume of NaOH solution. Heat gently and test the vapor evolved with moist red litmus paper and identify the gas.
- Make up another solution of D as above and test the pH with Universal Indicator solution. What conclusion can you draw?
Identify compound D and draw a diagram to show the structure and shape of the molecule. Indicate clearly the positions of any lone pairs of electrons.
Chemical Tests Observations
After adding D to equal amounts of sodium hydroxide, water and heating gently the solution was transparent. Placing Red Litmus Paper at the edge of the boiling tube tested the gas given off. The red litmus paper turned blue.
After adding the universal indicator to the boiling tube the color changed from green to blue.
Chemical Tests Results
The gas given was Ammonia and the, prove was that the red lithmus changed to blue.
- The changing of the color of the universal indicator proved that the compound was alkaline.
Identity And Structure
The unknown compound D is likely to be Urea.
Structure:
Compound E
Composition: C = 88.2%
H = 11.8% E.F. = C5H8
Mr = 136 M.F. = C10H16
Compound E is aliphatic. It contains a 6-membered ‘cyclohexene’ ring with 2 side branches on carbons 1 and 4.
A natural product, E is an oily liquid and belongs to a class of compounds called TERPENES. It can be extracted from oranges or lemons by distillation, makes up nearly 90% of the oils in their peels and is responsible for their characteristic odors.
Chemical Tests
- Add an equal volume of bromine solution and shake.
- Add an equal volume of acidified potassium manganate (VII) solution and shake.
Record your observations and conclusions; which functional group does E contain? Deduce the identity of Compound E and draw a full structural formula.
Compound E undergoes addition polymerisation under certain conditions. Draw the structure of the most likely product of polymerisation by showing TWO repeating units.
Chemical Tests Observations
- The yellow/orange of the bromine water solution goes colorless once when added to compound E.
- The purple color of the acidified potassium manganate goes colorless.
Chemical Tests Results
The bromine water and the acidified potassium manganate both going colorless is prove that there is a carbon – carbon double bound that comes due to the presence of an Alkene.
Identity And Structure
The unknown compound E is likely to be Limonene.
Structure:
Compound F
Formula = C3H7X, where ‘X’ is a halogen atom.
Chemical Test
Add a few drops of F to 2 cm3 of NaOH solution in a test tube then warm in a water bath for 3 – 4 minutes with occasional shaking. Acidify with about 3 cm3 of dilute nitric acid then add a few drops of silver nitrate solution. Note the appearance of any precipitate then test its solubility in excess dilute ammonia solution. Use your results to identify the halide in F.
By using the N.M.R. spectrum provided of Compound F I was able to determine the structure of F.
The isomer of F has the N.M.R. spectrum shown. Draw the structure of this isomer and account for the appearance of the spectrum.
Write equations for the reaction of Compound F with:
- Sodium cyanide dissolved in alcohol
- Alcoholic potassium hydroxide.
In each case name the organic product.
Chemical Tests Observations
In the beginning after adding the NaOH the solution remained clear and transparent. After heating the solution there were two layers that formed. A large lower layer and a smaller upper layer. The upper layer was less dense and a bit less transparent. After acidifying the lower layer turned cloudy and the upper layer remained the same. The solubility of the slightly creamy white precipitate was tested.
Chemical Tests Results
The conclusion drawn by testing the solubility is that the liquid is not miscible and the color of the precipitate tells us that the Halide X is Chlorine.
Identity And Structure
The unknown compound F is likely to be Propyl Chloride.
Structure: