c12 Flashcards
what is chromatography used for?
to seperate substances and provide information to help identify them
describe chromatography, and how you would find the Rf value.
draw start line on paper using pencil. place spot of food colouring on start line. place water in beaker / container. place (chromatography) paper in beaker / container so paper is in solvent but solvent is below start line. wait for solvent to travel up the (chromatography) paper (until near top). mark solvent front. dry the (chromatography) paper.
to find the r value:
* measure distance between start line and centre of spot
* measure distance between start line and solvent front
* use of measurements to determine Rf value
how can you tell a substance is pure?
they melt and boil at a specific and sharp temperatures. this is because mixtures have a range of melting and boiling points as they consist of different substances
meaning of pure in every day language
a substance that has nothing added to it - eg pure milk.
what is a formulation?
mixtures made up of substances in definite quantities designed to give products with desired properties
eg: paint, medicine
how can a chromatography be used to distinguish pure substances from impure substances?
the compouns in a mixture may seperate into different spots depending on the solvent, but a pure compound will only produce a single spot in all the solvents.
how to test for oxygen?
a glowing splint is inserted into a test tube of gas. if the splint relights, there is oxygen.
how to test for carbon dioxide?
an aqueous solution of calcium hydroxide (limewater) is used. when carbon dioxide is shaken with or bubbled through limewater, the limewater turns milky/ cloudy.
how to test for chlorine?
when damp litmus paper is put into chlorine gas, the litmus paper is bleached and turns white.
what are flame tests used for?
its used to identify some metal ions - cations.
colour lithium ion turns in flame test
crimson flame
colour sodium ion turns in flame test
yellow flame
colour potassium ion turns in flame test
lilac flame
colour calcium ion turns in flame test
orange-red flame
colour copper ion turns in flame test
green flame
colour aluminium solution turns when sodium hydroxide is added?
white precipitate
when NaOH is added in excess, colour is colourless.
colour calcium solution turns when sodium hydroxide is added?
white precipitate
colour magnesium solution turns when sodium hydroxide is added?
white precipitate
colour copper (II) solution turns when sodium hydroxide is added?
blue precipitate
colour iron (II) solution turns when sodium hydroxide is added?
green precipitate
colour iron (III) solution turns when sodium hydroxide is added?
brown precipitate
how can you identify a carbonate?
carbonates react with dilute acids to form carbon dioxide. carbon dioxide can be identified with limewater.
how can u identify a halide?
halide ions in solution produce precipitates with silver nitrate solution in the precense of dilute nitric acid.
silver chloride : white
silver bromide: cream
silver iodide: yellow
how can you identify a sulfate?
sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
advantages of instrumental methods over chemical tests
provide a greater accuracy, they are faster and easier to use, they are automated and can perform multiple simultaneous sampling and testing, modern instruments are sensitive and can work with very small sample sizes.
what is flame emission spectroscopy and how does it work?
an instrumental method to analyse metal ions in solution.
the sample is put into a flame and the light given out is passed through a spectroscope. the output is a line spectrum that can be analysed to identify metal ions in the solution and measure their concentrations.
describe a flame test
clean platinum wire loop by dipping it in dilute HCl
hold the loop in a blue flame after setting up a bunsen burner (do this till it burns without any colour)
then dip the wire loop back into the sample you want to test
put the wire back into the flame and record the colour that the flame is
ionic equation for precipitate formation for calcium ion and sodium hydroxide
Ca2+ + 2OH- -> Ca(OH)2
ionic equation for precipitate formation for copper(II) ion and sodium hydroxide
Cu2+ + 2OH- -> Cu(OH)2
ionic equation for precipitate formation for iron(II) ion and sodium hydroxide
Fe2+ + 2OH- -> Fe(OH)2
ionic equation for precipitate formation for iron (III) ion and sodium hydroxide
Fe3+ + 3OH- -> Fe(OH)3
ionic equation for precipitate formation for aluminium ion and sodium hydroxide
Al3+ + 3OH- -> Al(OH)3
ionic equation for precipitate formation for magnesium ion and sodium hydroxide
Mg2+ + 2OH- -> Mg(OH)2
method for the sulfate ions test and ionic equation
use a dropping pipette to add a couple of drops of dilute HCl and a few drops of Barium Chloride solution to a test tube with the unknown solution. if the sulfate ions are present a white precipitate will form
Ba2+ + SO4 2- -> BaSO4
what is stationary phase?
it is contained on the paper and does not move through it
how do substances separate by chromatography?
- solvent moves through paper
- different dyes have different attractions for paper and different solubilities in solvent
- therefore they are carried different distances
