Chemical Analysis Flashcards
What is a pure substance and how can you distinguish it from mixtures?
A pure substance is a single element or compound, not mixed with any other substance. They have specific melting and boiling points which can be used to tell them apart from mixtures.
What is a formulation?
A formulation is a mixture that has been designed as a useful product. Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties. Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
How does paper chromatography separate mixtures?
As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.
Suggest how chromatographic methods can be used for distinguishing pure substances from impure substances?
They would be easy to distinguish as a pure substance produces one spot on the chromatogram whereas an impure substance produces two or more spots.
How do you calculate the Rf value from a chromatogram?
Rf = distance moved by substance / distance moved by solvent
Describe the test for hydrogen
The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a squeaky pop sound.
Describe the test for oxygen
The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.
Describe the test for carbon dioxide
The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy).
Describe the test for chlorine
The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.
Describe the results that lithium, sodium, potassium, calcium and copper compounds produce in flame tests
- lithium compounds result in a crimson flame
- sodium compounds result in a yellow flame
- potassium compounds result in a lilac flame
- calcium compounds result in an orange-red flame
- copper compounds result in a green flame
What happens to solutions of aluminium, calcium and magnesium ions when a sodium hydroxide solution is added?
They form white precipitates when sodium hydroxide solution is added
What are the results of adding sodium hydroxide to solutions of copper(II), iron(II) and iron(III).
Copper(II) forms a blue precipitate.
Iron(II) forms a green precipitate.
Iron(III) forms a brown precipitate.
How would you test for halide ions in a solution
Add a silver nitrate solution and dilute nitric acid. Silver chloride is white
Silver bromide is cream
Silver iodide is yellow
(cats with brains can ideally yodel)
How would you test for sulfate ions in a solution
Sulfate ions in a solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
