Chemical Analysis AQA 2016 Chemistry topic 8 W Richards 10/11/2018 10/11/2018 Chemical Analysis AQA 2016 Chemistry topic 8 W Richards The Weald School

8.1 Purity, Formulations and Chromatography 10/11/2018 8.1 Purity, Formulations and Chromatography

Are the following pure or impure? Pure Substances 10/11/2018 A “pure” substance is defined as a substance that doesn’t contain any impurities (i.e. anything other than the substance it’s supposed to be). Are the following pure or impure?

Boiling Points of Mixtures 10/11/2018 Pure elements and compounds boil at specific temperatures (e.g pure water boils at 100OC). However, what happens when you have a mixture? % of ethanol % of water Boiling Point (OC) 100 78 80 20 82 60 40 90 94 98 Some questions: What temperature does pure ethanol boil at? What effect does adding ethanol have to the boiling point? What would be the boiling point of a 50/50 mix?

Formulations 10/11/2018 Formulations are mixtures that have been made from specifically measured quantities in order to give the mixture a particular purpose. Some examples:

Words – chemicals, paper, solvent, sizes, reference Chromatography 10/11/2018 Chromatography is a technique used to find out what unknown mixtures are made of. Substances are separated by the movement of a “mobile phase” through a “stationary phase”. In paper chromatography, the _____ is the stationary phase and the ______ is the mobile phase. R G B Different _____ spread out and stop at different points due to their different ____ and properties. They can then be identified by comparing to standard ________ materials. Words – chemicals, paper, solvent, sizes, reference

Chromatography 10/11/2018 Chromatography can be used to separate a mixture of different inks. Some example questions… R G B X 1 2 3 Z 1) Ink X contains two different colours. What are they? 2) Which ink is ink Z made out of?

Rf value 10/11/2018 The Rf value is a way of measuring how far a substance has moved: This line marks the distance travelled by the solvent R G B Rf value = Distance travelled by substance Distance travelled by solvent

Example questions Calculate the Rf values of the following: 10cm 8cm 10/11/2018 Calculate the Rf values of the following: R G B 10cm 2cm 8cm 5cm

8.2 Identification of Common Gases 10/11/2018

Testing for hydrogen 10/11/2018 “POP”

Testing for Oxygen 10/11/2018 Oxygen will relight a glowing splint

Testing for Carbon Dioxide 10/11/2018 Limewater Limewater turns milky/cloudy Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water

Testing for Chlorine Chlorine “bleaches” damp indicator paper 10/11/2018 Chlorine “bleaches” damp indicator paper

8.3 Identification of ions by spectroscopic means (Chemistry only) 10/11/2018 8.3 Identification of ions by spectroscopic means (Chemistry only)

Flame tests 10/11/2018 Compound Colour of flame

Q. What would happen if you used a mixture of chemicals? Flame tests 10/11/2018 Compounds containing lithium, sodium, potassium, calcium and copper metal ions (“cations”) can be recognised by burning the compound and observing the colours produced: Lithium Red Sodium Yellow Potassium Lilac Calcium Brick red Copper Green Q. What would happen if you used a mixture of chemicals?

Precipitation Reactions 10/11/2018 A precipitation reaction occurs when an insoluble solid is made by mixing two ionic solutions together. Method: 1) Mix the reactants together 2) Filter off the precipitate 3) Wash the residue 4) Dry the residue in an oven at 50OC

Metal Hydroxides 10/11/2018 Sodium hydroxide can be used to identify some metal ions (cations). Consider calcium chloride: Ca2+(aq) + OH- Ca(OH)2 (s) 2 Metal ion Precipitate formed Colour Calcium Ca2+ Calcium hydroxide: Ca2+(aq) + OH-(aq) Ca(OH)2 (s) White Aluminium Al3+ Aluminium hydroxide: Al3+(aq) + OH-(aq) Al(OH)3(aq) Magnesium Mg2+ Magnesium hydroxide: Mg2+(aq) + OH-(aq) Mg(OH)2 (s) Copper(II) Cu2+ Copper hydroxide: Cu2+(aq) + OH-(aq) Cu(OH)2 (s) Blue Iron(II) Fe2+ Iron(II) hydroxide: Fe2+(aq) + OH-(aq) Fe(OH)2 (s) Green Iron(III) Fe3+ Iron(III) hydroxide: Fe3+(aq) + OH-(aq) Fe(OH)3(aq) Brown Q. Can you complete this table?

Testing for Carbonates 10/11/2018 Carbonates are compounds containing carbon and ________. When an acid is added to a carbonate the carbonate starts to _______. A gas called ______ _______ is produced. Carbon dioxide is tested for using limewater – it turns limewater _____. Words – cloudy, fizz, carbon dioxide, oxygen

Testing for halide ions 10/11/2018 For each test state: 1) The colour of the precipitate 2) What compound it is Test 1: Chloride ions Add a few drops of dilute nitric acid to the chloride ion solution followed by a few drops of silver nitrate. Precipitate formed = silver chloride (white) Ag+(aq) + Cl-(aq) AgCl(s) Test 2: Bromide and iodide ions: Add a few drops of dilute nitric acid followed by a few drops of silver nitrate solution again. A pale yellow precipitate should be formed for bromide ions and a darker yellow precipitate for iodide ions.

Testing for Sulphate ions 10/11/2018 Method: Add a few drops of dilute hydrochloric acid to the sulphate ion solution followed by a few drops of barium chloride. Precipitate formed = barium sulphate (white again)

Instrumental Methods 10/11/2018 Hi. We’re industrial scientists and we want to test for ions but use instrumental methods instead of things like flame tests. What are the advantages of doing these tests instrumentally? Advantages of instrumental methods: More accurate More sensitive Quicker

Flame Emission Spectroscopy 10/11/2018 Flame emission spectroscopy is an example of an instrumental method: Step 1: Burn the chemical and pass the light through a spectroscope: Step 2: Analyse the line spectrum output to identify the metal ion: Unknown ion Potassium Calcium