Organic Analysis Flashcards
Describe the test that identifies whether a primary, secondary or tertiary alcohol is present:
Add 10 drops of the alcohol to 2 cm³ of acidified potassium dichromate
Warm of the mixture gently in hot water bath
Wait for colour change:
Primary - orange solution turns green as an aldehyde is formed.
Secondary - orange solution turns green as ketone forms
Tertiary - nothing happens
State how you will identify between a primary or secondary alcohol using acidified potassium dichromate:
Add excess alcohol to 2 cm³ of acidified potassium dichromate solution in around bottom flask
Set up a flask set up the flask as part of distillation apparatus.
Gently heat the flask. The alcohol will be oxidised and the product will be distilled off, collect it.
Once you’ve collected the product you can use Fehling’s solution or Benedict’s solution to distinguish between aldehyde or ketone.
Describe how Fehling’s solution can identify between an aldehyde and a ketone:
Add 2 cm³ of Fehling’s solution to a test tube.
Add five drops of your solution to the test tube.
Put the test tube and hot water bath for a few minutes.
Results:
Aldehyde - the blue solution will give a brick red precipitate
Ketone - nothing happens
Describe how Benedict’s solution can be used to distinguish between an aldehyde and a ketone:
Add 2 cm³ of Benedict’s solution to a test tube.
Add five drops of your solution into the test tube.
Put the test tube in a hot water bottle for a few minutes
Results:
Aldehyde - the blue solution will give a brick red precipitative.
Ketone - nothing happens.
Describe how Tollens’ reagent is made and how it is used to distinguish between an aldehyde and a ketone.
Put 2 cm³ of 0.10 mol dm-³ silver nitrate solution in a test tube. (Colourless solution)
Add a few drops of dilute sodium hydroxide solution. (Light brown precipitate)
Add drops of dilute ammonia solution until the brown precipitate dissolves completely.
Please the test tube and a hot water bath, add 10 drops of the solution, wait for a few minutes.
Results:
Aldehyde - a silver mirror forms on the walls of the test tube
Ketone - nothing happens
Describe the bromine water test:
Add 2 cm³ of the solution that you want to test the test tube.
Add 2 cm³ of bromine water to the test tube.
Shake that test tube.
Results:
Alkene - the solution will decolourise
Not Alkene - nothing happens
What does the bromine water test for?
Alkenes
What is sodium carbonate used to test for?
Carboxylic Acids
Describe the sodium carbonate test used for carboxylic acids.
Carboxylic acids react with carbonates to form a salt, carbon dioxide and water.
1) add 2 cm³ of the solution that you want to test to test tube
2) add one small spatula of solid sodium carbonate
3) if the solution begins to fizz, bubble the gas that it produces through some lime water in a second test tube
Results:
Carboxylic acid: solution will fizz, gas produced, like water goes cloudy
Not carboxylic acid: nothing happens
What does the m/z show in mass spectrometry?
The molecular mass of the compound.
State what high resolution mass spectrometry is:
Some mass spectrometers can measure atomic and molecular mass is extremely accurately (to several decimal places). These are known as high resolution must spectrometers.
They can be used for identifying compounds that appear to have the same Mr when rounded to the nearest whole number.
Describe infrared spectroscopy:
In infrared spectroscopy, a beam of IR radiation is passed through the chemical.
The IR radiation is also absorbed by the covalent bonds in the molecule, increasing their vibrational energy.
Bonds between different atoms absorb different frequencies of IR radiation. Bonds in different places in molecule absorb different frequencies too.
An infrared spectrometer produces a graph that shows you what frequencies of radiation the molecules are absorbing. So you can use it to identify the functional groups in a molecule.
State what the fingerprint region identifies:
The fingerprint region identifies a molecule.
Describe the fingerprint region:
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 computer database to check this region of unknown compounds IR spectrum against those of known compounds. If the match is one of them, you know the molecule is.
Infrared spectroscopy can be used to find how pure the compound is, and identify any impurities. Impurities produce extra peaks in the fingerprint region.
Infrared radiation absorption is linked to what?
Global warming
