• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12

Identification of an Organic Unknown.

Extracts from this document...

Introduction

Identification of an Organic Unknown. In this investigation I will be supplied with an unknown compound containing one of the following functional groups: * Alkene * Primary alcohol * Tertiary alcohol * Aldehyde * Ketone * Carboxylic acid * Ester * Phenol Wet tests are chemical tests and are useful because they are qualitative and mainly based on observations. Dry tests are more quantitative and go into more detail because determine exact molecular structure. I will be carrying out wet test instead of dry tests because it is more economical as using chemicals is cheaper then using machines and all we need to determine is the functional group. By using a number of chemical tests I will need to identify the functional group present. Each test used to identify the functional group is dependant on the previous result. I will use a flowchart to demonstrate the paths. Alkenes are hydrocarbon chains which contain carbon-carbon double bonds, C=C. These consist of a sigma bond and a pi bond. The electron charge cloud of the C=C is the centre of attraction for electrophiles. In most reactions involving alkenes, electrophiles are added to the C=C to give saturated compounds. This means that the characteristic reactions of alkenes are addition reactions. To test for an alkene, bromine water can be used. The orange bromine decolourises if C=C is present. Equation for bromine water and ethene: C2H4 + Br2 C2H4Br2 Mechanism: Alcohols are compounds in which a hydroxyl (-OH) group is bonded to a saturated carbon atom. Primary and secondary alcohols undergo oxidation when reacted with a mixture of potassium dichromate (VI). In the reaction the orange dichromate (VI) ions are reduced to green chromium (III) ions. Primary alcohols oxidise to form aldehydes whereas secondary alcohols oxidise to form ketones. Primary alcohols -OH group is attached to a carbon that has three hydrogens whereas a tertiary alcohol has a -OH group which is attached to a carbon that has three R groups and no hydrogens. ...read more.

Middle

I will also add water to the Fehlings solution in a separate test tube and use it as a control to show it only reacts with aldehydes. Outcomes: a colour change to red/ brown precipitate indicates presence of aldehyde, no colour change suggests it is a ketone. Refer to hypotheses table. Justification: only aldehydes are easily oxidised to acids, ketones are not. Fehlings solution is an alkaline copper (Cu2+) solution, which becomes reduced to (Cu+), a red/ brown precipitate of Cu2O, and the aldehyde becomes oxidised to RCOO- Safety: follow general safety procedures. 3. Test for carboxylic acid Apparatus: * Sodium hydrogen carbonate * Pipette * 2 test tubes * Limewater * Clamp * Rubber tube Procedure: add sodium hydrogen carbonate solid to 2cm3 of the unknown in a test tube. If effervescence occurs then add bubbles to limewater in test tube attached to a clamp, should be bubbled by using a rubber tube. Outcomes: if effervescence occurs then the bubbles should be added to limewater. If the limewater turns milky/ cloudy this shows that carbon dioxide gas is being released. If there is no effervescence and limewater does not turn cloudy then therefore the unknown must either be ester, alkene, phenol or alcohol. Justification: This shows that it is a carboxylic acid because it is the only compound in the unknown sample, which liberates carbon dioxide. The hydrogen in the carboxylic acid is replaced by sodium and water and carbon dioxide are also formed. Safety: follow general safety procedures. Be careful with apparatus to avoid breakages. 4. Test for phenol Apparatus: * FeCl3 crystals * Water * Test tube Procedures: dissolve crystals of FeCl3 in 2cm3 of water and add to 2cm3 of the unknown organic. Also add crystals to a test tube of water to use as a control to show it doesn't react with other groups and compare results. Outcome: a colour change to purple/ violet suggests that it is a phenol however if there is no change then it is an ester, alkene or alcohol. ...read more.

Conclusion

I reason I chose that I would use Iron (III) Chloride test before using bromine water is because phenol and alkene both react with bromine water whereas only phenol reacts with the Iron (III) Chloride and not alkene. I will also use sodium after testing for Primary alcohol because all alcohols react with sodium however tertiary alcohols do not react with oxidising agents and if previous test is negative then it can only test for tertiary alcohols as you can see in the flow chart. My flow chart I feel is very reliable and precise because each test is dependant on previous result and the reagents will not react with other functional groups as set out in my flow chart. I can confidently say my methods and equipment are reliable and accurate to prove my results valid even though certain variables cannot be controlled. After identifying the functional group present, infra red spectra and mass spectrum can be used to confirm results and identify structure. Precautions must be taken when handling: * 2, 4-dinitrophenylhydrazine as it toxic by skin contact * Eye protection must be worn at all times in the lab. * Be certain that there are no flammables in the area when lighting a flame. * Be alert for hazards in the lab. Do not proceed with any experiment until you understand the hazards involved. * Report all injuries to your instructor, even if they appear to be minor. * Do not come into contact with any of the solvents or reagents used in this lab other than soap and water. Remove gloves and wash hands before leaving lab. * Clean up all chemical spills immediately, this includes drips on bottles. * Do not leave any bottle uncapped. * Dispose of all wastes as directed. (Ask before you dump.) Cleaning Up: 1. Discard wastes for each test after consulting the teacher 2. Return all standard samples and test reagents to their original sources. 3. Wipe down your work area of the lab bench with a damp sponge/ tissue. 4. Place all equipment and apparatus in their correct location. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Aqueous Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Aqueous Chemistry essays

  1. Peer reviewed

    Identification of an Organic Unknown.

    4 star(s)

    SAFETY: Follow general safety procedures and bromine water can be toxic and corrosive so always make reference to the hazcards. 3. Test with 2, 4 DNP (2, 4-dinitrophenylhrazine) EQUIPMENT: Test tube Pipettes 2, 4 DNPH solution 1cm� of Ethanol Water Bath PROCEDURES: To 1cm� of 2, 4-dinitrophenylhydrazine solution and 1cm�

  2. The aim of this experiment is to answer the following question: What is the ...

    go down, if it does then that would change the amount of acid and make the experiment inaccurate. I will help to maintain accuracy by placing the titration apparatus close to the water bath. I will also have the titration equipment already set up, so the titration could be done immediately.

  1. Identification of an unknown organic compound

    groups and are therefore named as the carbonyl groups. Aldehydes are unsaturated as they contain less than maximum possible number of hydrogen's. When naming Aldehydes, they have the suffix of -al. E.G. ethanal and they have the common structure of: O // R---C \ H The bond angles in Aldehydes are close to 120 and are trigonar planar in

  2. identifying an unknown compound

    Primary Alcohol (C-OH) 5cm3 samples of the remaining five are placed in boiling tubes. 2cm3 of aqueous potassium dichromate (VI) followed by 4cm3 of dilute sulphuric acid is added to each of the solutions. 1. Samples are gently boiled in water bath and observed for colour change.

  1. ‘The Relative Strength of an Unknown Acid’.

    Therefore a reading of 1.324g indicates that the weight of the material is between 1.3235g and 1.3245g. So hence if the balance reading is accurately recorded, it may still have an error of 0.0005g. Because the mass of the substance is so small a greater error may result, an error of 0.05% could result from weighing a 1.00g sample.

  2. In this investigation I will get a number of unknown organic compounds to which ...

    The oxygen in the -OH group has two lone pairs of electrons, these can overlap with the delocalised ? electrons. Overall, the ? electron charge density is increased (especially at the 2, 4 and 6 positions). This is why this reaction happens only with phenol and not with the carboxylic acid.

  1. Titration with a primary standard.

    Touch the tip to a clean side of the slop bucket to remove any partial drop from the tip. Place the tip of the pipet in a clean Erlenmeyer flask and release your finger from the top. Let the pipet drain by gravity, 10-20 seconds after the pipet is empty,

  2. Identification of an organic unknown.

    In other words, bring together the functional groups that have similar structures. The six functional groups have either a '-OH' or an '=O' element in them (or in the case of the carboxylic acid, both elements are present.) A simple test can be done to determine which group is present.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work