Organic Analysis Flashcards
How can you discern between Primary and Secondary alcohols?
1) Add excess alcohol to 2cm3 of acidified potassium dichromate solution in a round-bottomed flask
2) Set up the flask as part of the distillation apparatus
3) Gently heat the flask- the alcohol will be oxidized and the product will be distilled off immediately
4) Test whether the product is a ketone or an aldehyde using Fehling’s solution and Benedict’s solution
How can you test whether you’ve got a Primary, Secondary, or tertiary alcohol?
1) Add around 10 drops of the alcohol to 2cm3 of acidified potassium dichromate in a test tube
2) Warm the mixture gently in a hot water bath
3) Observe a color change
Primary: The orange solution slowly turns green as an aldehyde forms (if continue heating then you’ll get a carboxylic acid)
Secondary: The orange solution slowly turns green as a ketone is formed
Tertiary: Nothing happens
How can you identify whether a solution is a ketone or aldehyde? (B & F)
1) Add 2cm3 of either benedicts or Fehling’s solution to a test tube. (should be a clear blue liquid)
2) Add 5 Drops of the aldehyde or ketone to the test tube
3) Put the test tube in a hot water bath to warm it for a few minutes
Aldehyde: should go brick red precipitate
Ketone: nothing happens
How can you identify whether a solution is a ketone or aldehyde? (T)
1) Put 2cm3 of 0.10 mol dm-3 silver nitrate solution in a test tube
2) Add a few drops of dilute sodium hydroxide solution. A light brown precipitate should form
3) Add drops of dilute ammonia solution until the brown precipitate dissolves completely
4) Place the test tube in a hot water bath and add 10 drops of aldehyde or ketone. Wait for a few minutes
Aldehyde: A silver mirror (a thin coating of silver) forms on the walls of the test tube.
Ketone: Nothing happens
How do you test for alkenes?
Bromine water test
1) Add 2cm3 of the solution that you want to test to a test tube
2) Add 2cm3 of bromine water to the test tube
3) Shake the test tube
Alkene: The solution will go from orange to colorless
Not alkene: The solution will remain orange
How do you test for carboxylic acids?
Carboxylic acids react with carbonates to form a salt, carbon dioxide, and water.
1) Add 2cm3 of the solution you want to test to a test tube
2) Add 1 small spatula of solid sodium carbonate or 2cm3 of sodium carbonate solution
3) If the solution begins to fizz, bubble the gas through lime water in another test tube.
Carboxylic acid: The lime water should go from clear to cloudy
Not carboxylic acid: Nothing happens
How can mass spectroscopy help to identify compounds?
You can find out the relative molecular mass of a compound. A molecular ion is formed when a molecule loses an electron. The molecular ion produces a molecular ion peak on the mass spectrum of the compound. The mass/charge ratio of the molecular ion peak will be the same as the molecular mass of the compound.
What is high-resolution mass spectroscopy?
High-resolution mass spectrometers are mass spectrometers that can measure atomic and molecular masses extremely accurately. They are useful in identifying compounds that appear to have the same mass number when they are rounded.
How does infrared spectroscopy help you to identify organic molecules?
In infrared spectroscopy, a beam of IR radiation is passed through a chemical. It is absorbed by the covalent bonds in the molecules, increasing their vibrational energy. Bonds between different atoms absorb different frequencies of IR radiation. Bonds in different places in a molecule absorb different frequencies too. An IR spectroscope produces a graph to show you what frequencies the molecules are absorbing- which you can use to identify the functional groups in a molecule.
What are ‘fingerprint regions’ on a graph produced by an Infrared spectroscope?
The region between 500 cm-1 and 1500 cm-1 is called the fingerprint region. It’s unique to a particular compound. You can use a computer database to check this region of an unknown compound’s IR spectrum against those compounds. If it matches one of them, you know what the molecule is.
This is also a good way to see how pure a compound is- extra peaks in the fingerprint region are impurities.
How is Infrared radiation absorption related to global warming?
- some of the EM radiation emitted by the sun reaches the earth and is absorbed. The earth then re-emits some of it as infrared radiation (heat)
- Molecules of greenhouse gases, like carbon dioxide, methane, and water vapor, in the atmosphere absorb this infrared radiation. They then re-emit some of it back towards the earth, keeping us warm. This is called the ‘greenhouse effect’
- human activities such as burning fossil fuels and leaving rubbish to rot in landfill sites have caused a rise in greenhouse gas concentrations.
- this means more heat is being trapped and the earth is getting warmer- leading to global warming.
