Organic analysis

• What is potassium dichromate (VI)?

  An oxidising agent
• What can potassium dichromate oxidise?

  Primary and secondary alcohols to form aldehydes and ketones
• Outline the test for the presence of primary, secondary or tertiary alcohols.

  -Add 10 drops of the alcohol to 2cm3 of acidified potassium dichromate solution in a test tube

  -Warm the mixture gently in a hot water bath

  -Watch for a colour change

  -With primary and secondary alcohols the orange solution slowly turns green as an aldehyde or ketone forms

  -No colour change is seen with tertiary alcohols.
• How do you test for a primary alcohol?

  -If you oxidise an alcohol under reflex and it tests positive for being a carboxylic acid, then it's a primary alcohol.

  
  

  -If you oxidise an alcohol under distillation conditions and it tests positive for being an aldeyde then it's a primary alcohol.
• How do you test for a secondary alcohol?

  If you oxidise an alcohol under reflex or distillation and it tests positive for being a ketone, then it's a secondary alcohol.
• What is Fehling's solution?

  Blue solution of complexed copper (II) ions dissolved ion sodium hydroxide.
• What is Benedict's solution?

  Same as fehlings but the copper (II) ions are dissolved in sodium carbonate instead of sodium hydroxide.
• How do you test for an aldehyde or ketone using the fehlings test?

  -Add 2cm3 of fehlings solution to a test tube

  -Add 5 drops of the aldehyde or ketone to the test tube

  -put the test tube in a hot water bath to warm it for a few mins

  -fehlings will reduce to a brick red precipitate when warmed with an aldehyde

  -no reaction happens with ketones, so solution will stay blue
• How do you test for an aldehyde or ketone using tollens reagent?

  -Put 2cm3 of 0.10 mol dm-3 silver nitrate solution in a test tube

  -Add a few drops of dilute sodium hydroxide solution. A light brown precipitate should form.

  -Add drops of dilute ammonia solution until the brown precipitate fully dissolves-tollens reagent.

  -The silver ions in tollens reagent are reduced to silver metal when warmed with an aldehyde, but not with ketone.

  -The silver will coat the inside of the apparatus to form a silver mirror.
• What are carboxylic acids?

  Carboxylic acids have a functional -COOH group and their names end in -anoic acid.

  They are formed by oxidising aldehydes or primary alcohols.
• How do you test for a carboxylic acid?

  -Add 2cm3 of the solution that you want to test to a test tube.

  -Add 1 small spatula of solid sodium carbonate or solution.

  -If the solution begins to fizz, bubble the gas that it produces through some limewater in a second test tube.

  -If the solution tested contains a carboxylic acid then carbon dioxide gas will be produced. When carbon dioxide is bubbled through limewater, limewater turns cloudy.
• How to test for an alkene?

  -Add 2cm3 of the solution that you want to test to a test tube

  -Add 2cm3 of bromine water to the test tube

  -Shake the test tube

  -If an alkene is present bromine water decolourises, orange colour disappears goes colourless.
• What can high resolution mass spectrometry measure?

  Can measure atomic and molecular masses extremely accurately, this can be useful for identifying compounds that appear to have the same Mr when they're rounded to the nearest whole number.
• What happens in infrared spectroscopy?

  -A beam of infrared radiation is passed through a sample of a chemical.

  -The IR radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy.

  -Bond between different atoms absorb different frequencies of IR radiation.
• What does the graph that the infrared spectrometer show?

  Shows you what frequencies of radiation the bond in the molecules are absorbing. So you can use it to identify the functional groups in the molecule.
• What is the fingerprint region?

  Region between 1000-1550cm-1 on the spectrum
• What's on the x axis and y axis of an infrared spectrum graph?

  X axis = wave number (cm-1)

  Y axis = transmittance (%)
• The more IR radiation a molecule absorbs...

  The more effective they are as greenhouse gases