AQA Chemistry A-level 3.3.6: Organic Analysis Detailed Notes PDF
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This document provides detailed notes on Organic Analysis for A-Level Chemistry, focusing on tests for functional groups, mass spectrometry, and infrared spectroscopy. Includes key concepts such as how different compounds react and are identified.
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AQA Chemistry A-level 3.3.6: Organic Analysis Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...
AQA Chemistry A-level 3.3.6: Organic Analysis Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-cc 3.3.6.1 - Tests for Functional Groups Alcohols 1o and 2o alcohols are identified using a cidified potassium dichromate. It turns from orange to green if they are present. 3o alcohols are not oxidised and the potassium dichromate remains orange. Example: Aldehydes Tollen’s reagent can be used to identify aldehydes. It is added to the solution being tested and warmed gently. If an aldehyde is present, a silver mirror will form in the test tube. If not, the solution will remain colourless. Example: Fehling's solution is another way of testing for aldehydes. It is added to the solution being tested and heated. A brick red precipitate will form if an aldehyde is present and if not, the solution remains blue and there is no observed change. Example: Alkenes Bromine water is used to test for unsaturated hydrocarbons. It changes from orange-brown to colourless if a carbon-carbon double bond is present. If not, no change is observed. Example: Carboxylic Acid These compounds react with sodium carbonate as acids, producing CO2. This gas can be collected and tested using limewater. This solution will turn cloudy if the gas is CO2. Example: 3.3.6.2 - Mass Spectrometry This analytical technique is used to identify compounds and determine their molecular formula (see 3.1.1). High Resolution Mass Spectrometry This is a much more sensitive form of mass spectrometry which allows the Mr of a substance to be determined to several decimal places. Precise atomic masses are always given and can then be used to calculate the molecular formula of the compound being tested. 3.3.6.3 - Infrared Spectroscopy This analytical technique uses infrared (IR) radiation to determine the functional groups present in organic compounds. The IR radiation is passed through a sample where the different types of bonds absorb the radiation in different amounts. These varying amounts of absorbance are measured and recorded allowing certain bonds and therefore functional groups to be identified. A spectrum is produced from the measurements which has characteristic curves for the different functional groups: -OH Alcohol Group . The characteristic peak is in the range 3230 - 3550 cm-1 -OH Acid Group . The characteristic peak is in the range 2500 - 3000 cm-1 C=C Unsaturated Group . The characteristic peak is in the range 1620 - 1680 cm-1 C=O Carbonyl Group . The characteristic peak is in the range 1680 - 1750 cm-1 Fingerprint Region Each IR spectrum has a fingerprint region to the right-hand side. This contains tiny differences from species to species which act as a molecules ‘fingerprint’, allowing it to be identified. Global Warming Infrared absorption also occurs in the atmosphere with molecules such as ozone. This causes heat to be trapped within the Earth’s atmosphere, an important factor for the existence of life here. However when chemicals such as CFCs are released into the atmosphere from human activity, this heating effect is enhanced, leading to global warming.
