Chemical Analysis

• Everyday life purity - a substance with nothing added to it, it is in its natural state
• Chemistry purity - a pure substance is something that only contains one compound or element throughout, boils and melts at a specific temperature
• Testing the purity of a substance - Measure the melting or boiling points of the sample and compare it to the melting or boiling of the pure substance (from a data book). The closer the sample boiling or melting point to the actual melting or boiling point, the purer the sample. Impurities will lower the melting point and increase the me.tong range. Impurities will increase the boiling point and range.
• Formulations - Useful mixtures with a precise purpose that are made by following a formula. Each component is a measured quantity and contributes to the properties of the formulations so it meets a required function. - E.g.

  paint: pigment (colour), solvent (gets rid of lumps), binder (holds the pigment in place), additives (added to changed physical and chemical properties of the paint further)
• The pharmaceutical industry can use formulations of a pill to change the drug so it is delivered to the correct part of the body, that its consumable and has a long shelf life
• Everyday formulations - cleaning products, fuels, cosmetics, fertilisers, metal alloys
• Testing for gases - Chlorine - bleaches damp litmus paper turning it white
• Testing for gases - Oxygen - will delight a glowing splint when out inside a test tube containing oxygen
• Testing for gases - Carbon dioxide - bubbling through lime water will turn it cloudy
• Testing for gases - Hydrogen - if you hold a burning splint at the open end of a test tube you’ll get a ’squeaky pop’ sound
• Paper chromatography - method - 1) Draw the base line in pencil (2) Spot each food colouring on the base line (3) Label to spots in pencil with their original colour (4) Add water into a beaker (5) Roll the top of the paper around a glass rod and tape it (6) Place the paper in the beaker, do not submerge the food colouring spots in water (7) Remove the paper once all the colours in the ink have been spread out (8) Draw where the solvent reached in pencil
• Paper chromatography - mobile phase - where molecules can move (solvent)
• Paper chromatography - stationary phase - where molecules can’t move (paper)
• Chromatography- A technique used to separate mixtures of substances based on their solubility
• Rf value is the ratio between the distance travelled by the dissolved substances (the solute) and the distanced travelled by the solvent
• Rf = distanced travelled by substance / distance travelled by solvent
• Testing for Cations - Different metal ions produce different flame colours when they heated. As the ions heat up their electrons move to higher energy levels. When the electrons drop back to their original energy levels, they release energy as light.
• Testing for cations - Flame tests - 1) Dip a clean wire loop into a solid sample of the compound being tested (2) Put the loop into the edge of the blue flame from a Bunsen Burner (3) Observe and record the flame colour produced
• Testing for Cations - Flame test results - Lithium (Li+) crimson flame
• Testing for Cations - Flame test results - Sodium (Na+) yellow flame
• Testing for Cations - Flame test results - Potassium (K+) lilac flame
• Testing for Cations - Flame test results - Calcium (Ca 2+) orange-red
• Testing for Cations - Flame test results - Copper (Cu 2+) green
• Testing for Cations - Flame test - Thismethod only works with single metal ion compounds as if a sample is tested and contains a mixture of metal ions, the flame colours of some ions may be hidden by the colours of others
• Testing for Cations - Coloured precipitates with Sodium hydroxide - Many metal hydroxides are insoluble and precipitate out of the solution when formed. You can testing for cations by adding a few drops of sodium hydroxide to your mystery compound.
• Testing for Cations - Coloured precipitates with Sodium hydroxide results - Calcium, Ca 2+ (aq) + 2OH - (aq) —-> CaOH (s), forms white precipitate
• Testing for Cations - Coloured precipitates with Sodium hydroxide results - Copper (II), Cu 2+ (aq) + 2OH - (aq) —-> Cu(OH)2 (s), Blue precipitate
• Testing for Cations - Coloured precipitates with Sodium hydroxide results - Iron (II), Fe 2+ (aq) + 2OH - (aq) —-> Fe(OH)2 (s), green precipitate
• Testing for Cations - Coloured precipitates with Sodium hydroxide results - Iron (III), Fe 3+ (aq) + 3OH - (aq) —-> Fe(OH)3 (s), Brown precipitate
• Testing for Cations - Coloured precipitates with Sodium hydroxide results - Aluminium, Al 3+ (aq) + 3OH - (aq) —-> Al(OH)3 (s), white precipitate
• Testing for Cations - Coloured precipitates with Sodium hydroxide results - Magneisum, Mg 2+ (aq) + 2OH - (aq) —-> Mg(OH) 2 (s), white precipitate
• Testing for Cations - Coloured precipitates with Sodium hydroxide - We need to be able to distinguish between aluminium, magnesium and calcium as they all produce the same white precipitate when reacting with sodium hydroxide. To do this we add excess sodium hydroxide to each solution. Aluminium hydroxide precipitate dissolves to form a colourless solution. Calcium hydroxide is unchanged. Magnesium hydroxide is unchanged. You can then distinguish between the magnesium and calcium with a flame test as the calcium will produce an orange-red flame.
• Testing for Anions - Carbonates - carbonates are substances that contain CO3 -2 ions
• Testing for Anions - Carbonates - 1) Add a few drops of dilute hydrochloric acid to a test tube into the unknown substance (2) Collect any gas formed in a plastic pipette and bubble it through some limewater (3) If carbonate ions are present the limewater will turn cloudy - Na2CO3 (aq) + 2HCL (aq) ---> CO2 (g) + 2NaCl (aq) +H2O (l)
• Testing for Anions - Sulfates - substances containing SO4 -2 ions
• Testing for Anions - Sulfates - 1) Use a dropping pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution to a test tube containing the sample (2) If sulfate ions are present a white precipitate will form - Ba 2+ (aq) + SO 4 -2 (aq) ---> BaSO4 (s)
• Testing for Anions - Halides (chloride) - 1) Add a couple of drops of dilute nitric acid followed by a couple of drops of silver nitrate solution to the unknown solution (2) If chloride ions are present a white precipitate will form - Ag+ (aq) + Cl- (aq) ---> AgCl (s)
• Testing for Anions - Halides (bromide) - 1) Add a couple of drops of dilute nitric acid followed by a couple of drops of silver nitrate solution to the unknown solution (2) If bromide ions are present a cream coloured precipitate will form - Ag+ (aq) + Br- (aq) ---> AgBr (s)
• Testing for Anions - Halides (iodide) - 1) Add a couple of drops of dilute nitric acid followed by a couple of drops of silver nitrate solution to the unknown solution (2) If iodide ions are present a yellow precipitate will form - Ag+ (aq) + I- (aq) ---> AgI (s)
• Flame emission spectroscopy - A sample is place in a flame. As the ions heat up their electrons move to higher energy levels. When the electrons drop back to their original energy levels they release as light. The light passes through a spectroscope which and detect different wavelengths of light and as a result produce a line spectrum.