Chemistry Topic 8 Chemical Analysis Pure Substances and formulations Describe how to carry out a Nichrome/platinum loop/wire dip in sample/place in roaring Pure Substances In chemistry, a pure substance is a single element or compound, flame test. flame/ observe colour of the flame. not mixed with any other substance. Pure elements and compounds melt and boil at specific What is the main problem If a sample containing a mixture of ions is used some flame temperatures. Impure substances melt over a range. with flame tests? colours can be masked. What solution is used for the Sodium hydroxide solution can be used to identify some metal Everyday pure substance In everyday language, a pure substance can mean a substance precipitate test? ions (cations). that has had nothing added to it, so it is unadulterated and in its 2- natural state, e.g. pure milk. Sulfate test (SO4 ) Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid. How to determine if a Pure elements and compounds melt and boil at specific Carbonates react with dilute acids to form carbon dioxide gas. 2- substance is pure temperatures. Impure substances melt over a range. Carbonate test (CO3 ) Carbon dioxide can be identified with limewater. Advantages of Instrumental Accurate, sensitive, rapid Halide ions in solution produce precipitates with silver nitrate methods of chemical tests. Halide test (Cl-, Br-, I-) solution in the presence of dilute nitric acid. Silver chloride is Flame Emission The sample is put into a flame and the light given out is passed white, silver bromide is cream and silver iodide is yellow. Spectroscopy through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations. Flame Tests (Cations) Precipitate Tests (Cations) Metal Ion Flame Colour Metal Ion Precipitate Colour Chromatography: a separating technique. + Magnesium Mg2+ White – (negative flame test) Lithium Li Crimson + 2+ Sodium Na Yellow Calcium Ca White – (red flame test) Stationary phase (paper) and a mobile phase (solvent). 3+ Potassium K+ Orange Aluminium Al White (dissolves in excess NaOH) Separation depends on solubility and attraction to the paper(stationary phase). 2+ Calcium Ca2+ Red Copper Cu Blue Iron (II) Fe2+ Green The ratio of the distance moved by a compound (centre of spot from origin) to the Copper Cu2+ Green Iron (III) Fe3+ Brown distance moved by the solvent can be expressed as its Rf value: Rf = distance moved by substance Insoluble Precipitates: distance moved by solvent copper sulfate + sodium hydroxide → sodium sulfate + copper hydroxide Different compounds have different Rf values in different solvents, which can be used CuSO4(aq) + 2NaOH(aq) → Na2SO4(aq) + Cu(OH)2(s) Required Practical to help identify the compounds.

The compounds in a mixture may separate into different spots depending on the Gas Tests Method solvent but a pure compound will produce a single spot in all solvents.

Oxygen Glowing splint inserted into a test Draw a pencil line 2cm from the bottom tube of the gas. The splint relights Mark 5 spots in pencil equal distance along the line in oxygen. Hydrogen A burning splint held at the open Use a capillary tube, put a spot of each sample on

end of a test tube of the gas. Burns the pencil dots rapidly with a pop sound. Add water to the beaker 1cm depth Carbon Aqueous solution of calcium Tape the paper to a glass rod, rest it on top of the Dioxide hydroxide (lime water). When carbon dioxide is shaken with or beaker – do not allow the samples to go in the water bubbled through limewater the Allow the solvent to travel up the paper limewater turns milky (cloudy). Use a pencil to show the distance the water travels Chlorine When damp litmus paper is put into Measure the distance the water has travelled chlorine gas the litmus paper is Measure the distance each sample has travelled bleached and turns white. Calculate Rf