The purpose of this lab is to identify two different unknown organic compounds, through investigating different chemical properties by various experiments. The chemicals could be alkanes (hexane), alkenes (hex-1-ene) or alcohols (methylpentan-1-ol or hexa

GCSE Science

Mohit Parkash, Elias Assaf N2A IEGS

Chemistry B Mr. Nicolas

“Identification of unknown organic compounds” 2011–10–28

Identification of unknown organic compounds

Mohit Parkash

Elias Assaf

Mr. Nicolas

Chemistry B

N2A

IEGS

Introduction;

We are provided with three sample bottles each containing 5-10 cm3 of aqueous solutions. Two of the compounds are pure organic substances while one substance is a mixture of the two pure organic compounds. The pure substances provided could possibly be Hexane, Hex-1-ene, Hexan-1-ol or methylpentan-1-ol.

Aim;

The purpose of this lab is to identify two different unknown organic compounds, through investigating different chemical properties by various experiments. The chemicals could be alkanes (hexane), alkenes (hex-1-ene) or alcohols (methylpentan-1-ol or hexan-1ol).

Background;

Alkanes, alkenes and alcohols are all organic compounds with different chemical/physical properties. Different chemical properties give different reactions with other substances, and different physical properties are for instance boiling point, melting point and density. By testing for their properties it is possible to determine what an unknown organic compound is.

Alkenes are very useful compounds that can be used for fuel and illuminant, for the manufacture of a variety of polymers and as raw material for the manufacture of industrial chemicals such as alcohols etc.

Alkanes are very useful compounds that can be used in the production of polymers and fuels.

The main uses for alcohols are as solvents for gums, resins etc.

This is why it is important to be able to determine what different substances are. If we can determine it we can used it for the production of other things.

Materials;

3 Unknown chemical substances (A56, B56, A+B56)
Bromine water (Br2)
Distilled water (H2O)
Paraffin oil ()
3 Test tubes with lids
Test tube rack
3 Pipettes
1 Beaker
3 Measuring cylinders
Water bath
Thermometer
Bunsen burner
Tripod

Safety Materials;

Safety goggles
Lab coat

Precaution;

Be careful when using unknown compounds, if you spill it on your skin it can become itchy and irritating, do not have something in the way that makes you uncomfortable while doing the experiment. Also, wear a lab coat and safety goggles to keep your clothes and eyes safe.

Method; (before lab investigation)

Take the 3 unknown compound bottles which are provided.
Add ___ ml of each unknown liquid into a distilled beaker to save “supplies” so different experiments can ...

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Safety Materials;

Safety goggles
Lab coat

Precaution;

Method; (before lab investigation)

Take the 3 unknown compound bottles which are provided.
Add ___ ml of each unknown liquid into a distilled beaker to save “supplies” so different experiments can be done, to be able to get as accurate results as possible
Now, test the solubility of the 3 liquids to be able to see which substance is which, alcohol, alkane or alkene. Because they all have different reactions with water.
If provided with both alkane and alkene, add some bromine water to see which is which since they both have different reactions with the substance.
If provided with the hexan-1-ol and/or methylpentan-1-ol, test their boiling points. The B.P of hexan-1-ol is between 155-159o C so by testing the B.P, it will be clear to see which is which since the isomer (methylpentan-1-ol) will have a less a B.P due to branching.
After having the first 2 substances identified, the 3rd unknown liquid can be determined since it’s a mix of the other 2!

Method; (after lab investigation)

Start off by cleaning the materials with distilled water.
Add 3 ml of your two pure substances into 2 different distilled test tubes. The rest can be used for further experimentation.
Now, test the solubility in water of the 2 liquids, if it is an alkane, alkene or an alcohol. Because they all have different reactions with water. (Hex-1-ene and Methylpentan-1-ol is insoluble .Hexane and Hexan-1-olis soluble)
Test your substances with bromine water. When alkenes are added to bromine water, the brownish color decolorizes and becomes transparent. Alkanes do not react with bromine water.
Check for alkanes. Alkanes do not react with bromine water; now check the boiling point of Hexane. Hexane boils at 70°C. Put the test tube in a water bath (70°C), if the substance boils it indicates that it is an alkane.
If provided with the hexan-1-ol and/or methylpentan-1-ol, test their boiling points. The B.P of hexan-1-ol is between 155-159oC so by testing the B.P, it will be clear to see which is which since the isomer (methylpentan-1-ol) will have a less a B.P due to branched chains.
The boiling points needs to be tested by heated up in paraffin oil, because it has a higher boiling point than the alcohols, if the alcohols would be heated up in water, the substance would not get any warmer than 100oC because water evaporates at a temperature over 100 oC.
After having the first 2 substances identified, the 3rd unknown liquid can be determined since it is a mixture of the substances you have identified.

Results;

Equations;

Sample A + Br2 → No reaction

Sample B + Br2 → Decolorzation

Sample A + H2O → Cloudy, Not really dissolved

Sample B + H2O →No reaction, Insoluble/2 layers

Sample A + Water bath (80oC) → No boiling, Not an alkane

Conclusion;

From the results it can be concluded that one of the organic compounds given were Hex-1-ene and Methylpentan-1-ol. To determine Hex-1-ene the properties for alkenes had to be tested. Alkenes consist of a carbon-carbon double bond; this means that when it reacts with a substance it will rupture the pi-bond, forming new single bonds. If alkenes mix with bromine it will decolorize and this was clearly the case when substance B56 was mixed with bromine. To be sure that B56 was hex-1-ene the solubility in water was tested; fortunately it was insoluble, proving the result correct.

But, alkanes do not react like alkenes when added to bromine water. Because alkanes only have single bonds, means that the bromine molecules are unable to bond because they can not bond to the saturated molecules. Therefore the colour will still remain brownish. This proved that B56 was not an alkane because the liquid decolorized.

To determine A56 it was tested for both alkane and alkene. However, it did not react as expected for alkanes and alkenes. Instead, it became cloudy in water which was a sign of it being methylpentan-1-ol. To be sure that it wasn’t an alkane or alkene it was boiled in the water bath. It did not boil at 75oC. This indicated that it must be an alcohol. When the boiling point was checked, it started boiling at 138oC when it was placed in paraffin wax and heated up by a Bunsen burner, which is really close to the estimated B.P. of methylpentan-1-ol. So it is sure that the substance was Methylpentan-1-ol.

Finally, the 3rd test tube was a mix of hex-1-ene and methylpentan-1-ol.

Evaluation;

The experiment was well performed according to the method, even if it could have been done better. Results of the different experiments may be a bit inaccurate, because different group members did different observations. The easiest way to improve this would be to have both group-members to observe every experiment together, to see when the reactants have fully reacted, which would give us more accurate results.

To avoid contaminating the substances used during the lab, one member of the group had to clean all equipments used, properly and thoroughly. When cleaning, distilled water and normal tap water was used, distilled water was only used on the equipment in a lot of contact with chemicals. If the equipments are not cleaned properly or not cleaned at all there could be some chemicals or residue left on the equipments. Then the substances used during the lab would later be contaminated if dirty equipments are used, this would thereby lead to inaccurate results. By cleaning all equipments used during the investigation the factor of getting inaccurate results due to contamination was cleared. After cleaning the equipments it was made sure that no water was left since this could lead to contamination as the water could interfere with the substances used during the investigation, this was done by wiping the water with a peace of paper. Also, if the water was not wiped out of the equipment such as the test tube that was used to check the boiling point of the alcohol, it could have affected our results of the boiling point of the alcohol since water has quite a low boiling point compared to alcohols.

Another thing we could have done better is that we could have stirred the paraffin oil when checking for the boiling point of the alcohol. It would be good to stir the oil so the heat is equally distributed, since the Bunsen burner just has a flame straight up into the middle of the beaker which makes the oil hotter in the middle than around it.

Another inaccuracy with the paraffin oil could be that the oil got heated up to fast due to a high flame from the Bunsen burner. The high flame may be too hot so the paraffin oil heated up but the thermometer was not fast enough to show the actual temperature of the paraffin oil.

Overall we are pleased with the results and the way the experiment was carried out. The results were fairly accurate of the experiments. To make this experiment more interesting we could have investigated other chemical properties, for example doing the match test for alcohols to get a full understandable knowledge about testing for unknown organic chemicals.

Peer Reviews

Here's what a star student thought of this essay

dragonkeeper13

20th of Jul 2012

Quality of writing

The candidate's spelling, punctuation, and grammar is very good throughout. However, their explanations and descriptions could have been clearer as they tended to use long sentences where a short bullet point or table could have been used, and often repeated themselves. Although headings have been used throughout, some information was still in the wrong sections, for example explanations of the chemistry behind the reactions were spread all over the report and often repeated, and all the information about reducing errors was included in the evaluation rather than in a 'reducing errors' section in the method. They have also not stuck to convention to give a fully detailed method - instead they simply order you to 'test the solubility' with no indication as to how to do this. A scientific report should allow the reader to precisely copy the author's method, and so needs more detail. they have ended the report well by suggesting one way to further develop on their analysis, having mentioned possible causes of errors. Overall, their quality of writing is acceptable, but the report needs proof reading and more detail.

Level of analysis

The candidate has carried out several tests, and used their results to analyse the substances. However, they do not appear to have thoroughly understood the tests - for example claiming that the fact that one substance did not boil at 75 degrees meant that it must be an alcohol - to support this they should have given the boiling points for all the substances and thus decided that the only ones above 75 degrees were alcohols, or described how they have eliminated the other possibilities (by earlier tests). This section of the report could have been written more clearly to clarify this. One test they have clearly understood and analysed well is the bromine test for unsaturation - they have given a very good explanation of the reaction. They have also shown knowledge of advanced chemistry by describing the differences in boiling point between branched and unbranched molecules.

Response to question

The candidate has written up an experiment they carried out to identify unknown substances. They included all the required sections - an introduction, method, results, conclusion, and evaluation. However, they have written the method and results sections out twice - proof checking should have spotted this, and their method lacks detail and a labelled diagram. However, they have used their results to identify the substances correctly and so come to a well-supported conclusion, and as part of this did an additional test on one substance to double check their results, showing a thorough, scientific approach.