3.6 Organic analysis

• Organic Analysis: Alcohols can be tested using acidified potassium dichromate, which oxidizes primary and secondary alcohols but not tertiary ones.
• The primary and secondary alcohols both give the same color change, so fractional distillation is used to distinguish between them.
• Aldehydes are produced from primary alcohols, so if an aldehyde is formed, the initial alcohol is primary.
• Ketones are produced from secondary alcohols, so if a ketone is formed, the initial alcohol was a secondary alcohol.
• Failing solution, also known as Benedict's, is an oxidizing agent that oxidizes aldehydes but not ketones.
• In the presence of failing solution, aldehydes form a blue solution that turns to a brick red precipitate, while ketones remain blue.
• Tollen's reagent is used to distinguish between aldehydes and ketones.
• Tollen's reagent consists of silver nitrate solution, which is colourless, and a few drops of sodium hydroxide and dilute ammonia.
• When Tollen's reagent is added to a solution containing aldehydes or ketones, a pale brown precipitate is formed.
• The pale brown precipitate in Tollen's reagent is insoluble, so it can be used to identify the presence of aldehydes or ketones.
• Ethanol, CH3CH2OH, and propane, C3H8, all have a molecular mass of 44 to the nearest whole number.
• The precise mass of carbon, hydrogen, and oxygen can be measured to four decimal places.
• High resolution mass spectrometry can distinguish between these two molecules.
• The molecular mass of propane, C3H8, can be calculated using these atomic masses.
• The frequency of infrared radiation absorbed by a covalent bond depends on the atoms either side of the bond and the position of the bond in the molecule.
• A peak at 3000 cm-1 suggests an OH as an acid.
• Standard mass spectrometry gives a mass to the nearest whole number.
• High resolution mass spectrometry can measure to several decimal places.
• High resolution mass spectrometry is useful when identifying different molecules with the same molecular mass rounded to the nearest whole number.
• The molecular mass of methanol, CH3OH, can be calculated using these atomic masses.
• Infrared spectroscopy uses infrared radiation to increase the vibrational energy of covalent bonds in a sample.
• The fingerprint region of an infrared spectrum is used to identify the functional groups present.
• A peak at 1700 cm-1 suggests a carbonyl group.
• An infrared spectrum of ethanoic acid can be assigned to identify what is present.
• If a ketone is present, no silver precipitates will be formed.
• Carboxylic acids are reacted with a carbonate to produce carbon dioxide gas.
• Mass spectrometry is used to determine the relative molecular mass or M R of a compound.
• When a molecule goes to a mass spectrometer, it is broken up into smaller bits called fragments.
• To use Tollen's reagent, add an aldehyde or a ketone to the reagent, place it in a hot water bath, and observe for a silver precipitate.
• Bromine water is used to test for alkene presence.
• Tollen's reagent is used to identify aldehydes and ketones.
• If an aldehyde is present, a silver precipitate will coat the inside of the flask.
• The molecular ion peak is the same as the molecular mass of the compound.
• The molecular mass of a compound can be determined by comparing the molecular ion peak to the molecular mass of known compounds.
• The molecule is knocked an electron off, leaving a positive charge, resulting in a +1 charge.
• Add bromine water to an alkene, shake, and observe for a colorless solution forming.
• Lime water turns cloudy if carbon dioxide is present, indicating the presence of a carboxylic acid.
• The mass divided by the charge is the molecular mass ratio, represented by the letter Z.
• The M plus 1 peak in mass spectrometry is the molecular ion peak, which shows the mass of the original molecule.