GCSE AQA Extension Science Chemistry Revision Notes

 Chemistry Revision

·         Tests for Cations (+)

o   Flame colour for identification= Sodium (Na)- Potassium (K)- Calcium (Ca2)- Copper(CU2)- lithium (Li)

o   Some metals form a coloured precipitate with NaOH

§ 

§  Cu2

§  Fe2

§  Fe3

§  Al3- white to colourless

§ 

o   Ammonium + NaOH= Ammonia

§  Ammonia stinks and turns damp red litmus paper, blue.

·         Tests for Anions (-)

o   Testing for Carbonates

§  Acid + Carbonate= Salt+ water+CO2

§  CO2 turns limewater cloudy

§  Also you can put 1 spatula of carbonate and heat strongly. Copper Carbonate goes green to black and stays black. Zinc Carbonate goes from white to yellow and back to white.

o   Testing for Sulfates

§  Add dilute hydrochloric acid followed by barium chloride solution

§  It goes white if compound was a sulphate

o   Testing for halides

§  Add dillute Nitric acid followed by silver nitrate solution

§  Chloride

§  Bromide

§  Iodide

o   Testing for nitrates

§  Add aluminium powder and sodium hydroxide and heat.

§  You’ll get ammonia ( tests for ammonia shown above)

·         Tests for Organic Compounds

o   Organic chemicals contain carbon and it’s compounds

o   Carbon’s presence causes them to burn when heated with a yellow orange or blue flame

o   Unsaturated organic moles contain C=C double bonds… they decolourise bromine water

·         Empirical Formulae & Combustion Analysis

o   The empirical formula is the simplest ratio of atoms in a molecule or compound

o   Combustion Analysis finds the empirical formula of a compound:

§  Compound’s mass is measured

§  It is burned in excess oxygen

§  CO2 and water produced is measured

§  Mass of Carbon x proportion of C in CO2 (12/44= 0.2727)

§  Mass of Hydrogen  x proportion of H in H2O (2/18= 0.111)

§  Divide theses masses by the atomic number of C and H (to find number of moles)

§  Divide by smallest to get simplest ratio.

·         Instrumental Analysis

o   Atomic Spectrometers- Analyse energy (usually light) using a line emission spectrum. Patterns are then matched to existing frequencies on a database

o   Infrared Spectroscopy- detects specific bonds in organic chemicals

o   Ultraviolet Spectroscopy- analyses levels of nitrates + phosphates in water

o   Nuclear magnetic resonance spectroscopy- used to detect some organic molecules

o   Gas-liquid chromatography- separates gases through a column- identified by the distance moved

o   Mass spectrometer- used for elements + ions. Masses of fragments used to identify what is in a sample.

·         Acids- Hydrogen (H+ )ions and proton donors

·         Alkalines-Hydroxide (OH– )ions and protons acceptors

·         Strong acid/alkali= completely ionised

·         Weak acid/alkali=Partially ionised

·         Titrations

o   Measure out 25cm3…