chemical analysis how can we tell what chemicals we have in front of us obtaining pure substances is very important when it comes to chemistry one way to tell if a substance is pure or not is by testing to see what its melting point or boiling point is if it's pure it should be a very specific temperature a formulation is a mixture that has been specially designed to be useful in a very specific way with very specific quantities of different substances used to make things like paints fuels Alloys fertilizers think of George's Marvelous Medicine as being the ultimate formulation chromatography is a way of separating substances in a mixture for example pigments in inks or drugs in a urine sample the stationary phase often special chromatography paper or just filter paper is what the substances move up with the help of the mobile phase often just water which Rises up the paper due to capillary action dragging lighter particles further up the stationary phase we draw the line at the bottom in pencil so it doesn't move with the solvent the water then at the end of the process we measure how far the solvent has moved and also how far the substance or substance is have moved to and these are both measured from that starting line we can then calculate an RF value that stands for a retention factor which is just a ratio of how far a spot has moved compared to the solvent so that ends up being a number between zero and one we can compare RF values of our spots with known RF values to identify what's in our mixture we can test for hydrogen by holding a burning splint over the test tube which will produce a squeaky pop oxygen will relight a glowing splint carbon dioxide will turn lime water cloudy when bubbled through it chlorine gas will bleach damp blue litmus paper that means turn it white we can test for some metals with flame tests lithium will produce a crimson flame sodium yellow potassium lilac calcium orange red and copper green we can test for other metals in solutions by adding sodium hydroxide aluminium calcium and magnesium in solution will produce a white precipitate however the aluminium hydroxide produce will then dissolve if excess sodium hydroxide is added copper 2 ion that is cu2+ ions form a blue precipitate Ion 2 green precipitate ion 3 Brown you might have to complete an ionic equation for these for example the copper and hydroxide ions making copper hydroxide and you got to make sure it's balanced too just three quick ones carbonates react with acids to make carbon dioxide gas and we know how to test for that we test for halide ions that's hallogen ions by mixing with silver nitrate solution and nitric acid if chlorine ions are present silver chloride is made that's a white precipitate silver bromide is cream and silver iodide is yellow finally sulfate ions will produce a white precipitate when mixed with barium chloride and hydrochloric acid of course all of these are chemical tests we can do in our school Labs but in proper Labs with lots of money they use instrumental methods to determine what substances they have these instruments are accurate sensitive and fast for example they can do flame emission spectroscopy flame tests on steroids the light produced by a flame is passed through a spectroscope which can identify exactly what wavelengths are being emitted say on an emission line Spectrum which can then be used to identify these metal ions so I hope you found that helpful leave a like if you did and pop any questions or comments below I'll see you in the next video