Booklet 8 - Purity, Formulations And Chromatography Flashcards
What is a pure substance in chemistry?
A pure susbatnce is a single element or compound, thats not mixed with any other substance
How can you test for the boiling and melting points of pure substances?
Pure substances melt or boil at specific temperatures
- melting and boiling points data can be distinguished pure substances from mixtures by testing the melting and boiling points of a substance and comparing it with the melting and boiling points of a pure substance, which you can find from the data book
How do you know if a sample is pure?
The closer the measured value if the substance is to the actual melting or boiling points the purer the sample is
What two things can impurities in a sample do?
1) . Lower the melting point and increase the melting range of the substance
2) . May also increase the boiling point and may result in the sample boiling at a range of temperatures
What is a pure substance in a everyday language?
It can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state eg pure milk
What is a formulation?
A mixture that has been designed as a useful product
- many products are complex mixtures in which each chemical has a particular purpose
How are formulations made?
They’re made by mixing the components in carefully measured quantities to ensure that the product has the required properties
What are some of the examples of formulations?
Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
What is chromatography?
Can be used to separate mixtures and can give information to help identify substances
What’s the mobile phase?
Where the molecules can move, always a liquid or a gas
What is the stationary phase?
Where the molecules cant move, can be a solid or really thick liquid
What does separation depend on?
the distribution of substances between the two phases
What is the process of chromatography?
1) . Draw a pencil line on the paper near the bottem using a ruler, pencil is used as ink would run
2) . Spot samples carefully onto the pencil line
3) . Hang in a beaker of solvent, ensuring that the pencil line is above the level of the solvent
4) . Close the lid and allow the solvent to rise up the paper
5) . When near the top, remove the paper and quickly mark with pencil where the solvent reached. This is the solvent front
6) . Allow paper to dry
What does the mobile stage move through?
The stationary stage, and anything dissolved in the mobile phase moves with it
What happens to chemicals that spend more time in the mobile phase than the stationary phase?
They’ll move futher in the stationary phase
What roles do the stationary and mobile phases play in paper chromatography?
The stationary phase is the chromatography paper and the mobile stage is the solvent
Who two things do molecules depend on regarding how much time they spend in a phase in chromatography?
1) . How soluble they are in the solvent
2) . How attracted they are to the paper
What happens to molecules with a high solubility in solvent (chromatography)?
They are also less attracted to the paper and will spend more time in the mobile phase and they’ll be carried futher up the paper
How can the ratio of the distance moved by a compound to the distance moved by the solvent be expressed?
As its Rr value
Rr = distance moved by substance ➗distance moved by solvent
What do different compounds have? (Chromatography)
They have different Rr values in different solvents, which can be used to help identify the compounds.
Why may compounds in a mixture separate into different spots?
It depends on the solvent BUT a pure compound will produce a single spot in all solvents
What is the test for hydrogen?
It uses a burning splint held at the open end of a test tube of the gad, the hydorgen burns rapidly with a pop sound
What is the test for oxygen?
Uses a glowing splint inserted into a test tube of a gas, the splint relights in oxygen
What is the test for carbon dioxide?
Uses an aqueous solution of calcium hydroxide (limewater), when CO2 is shaken with or bubbled through limewater, the limewater turns milky (cloudy)
What is the test for chlorine?
Uses litmus paper, when it is damp it is put into chlorine gas and the litmus paper is bleached and turns white
What are flame tests used for?
To identify some metal ions (cations), they all produce distinctive colours
What colour do lithium ions burn?
Crimson red flame
What colour do sodium ions burn?
A yellow flame
What colour do potassium ions burn?
A lilac flame
What colour do calcium ions burn?
A orange-red flame
What colour do copper ions burn?
A green flame
What is a drawback of the flame test technique?
If a sample contains a mixture of ions some of the flame colurs can be masked and therfore may not be noted
What solution can be added to indentify metal ions (cations)?
Sodium hydroxide solution
What colour precipitates do solutions of aluminium, calcium and magnesium ions form?
White precipitate when sodium hydroxide solution is added
What precipitate dissolves in excess sodium hydroxide solution?
Aluminium hydroxide precipitate
What ions form coloured precipitates when sodium hydroxide solution is added to it?
Solutions of copper (II), iron (II) and iron (III)
What colour precipitates do copper (II), iron (II) and iron (III) form?
- copper (II) forms a blue precipitate
- iron (II) forms a green precipitate
- iron (III) forms a brown precipitate
How do you test for carbonate ions in solution?
By reacting them with dilute acids to form carbon dioxide gas which can be identified with limewater test
How do you test for halide ions in solution?
Add dilute nitric acid followed by silver nitrate solution
What colours chloride, bromide and iodide go in the prescene of dilute nitric acid and silver nitrate solution?
- Chloride gives a white precipitate of silver chloride
- bromide gives a cream precipitate of silver bromide
- iodide gives a yellow precipitate of silver iodide
How do you test for sulfate ions?
Add dilute hydrochloric acid followed by barium chloride solution. If they’re present a white precipitate of barium sulfate will form
What are instrumental methods?
Elements and compounds can be detected and identified using imstrumental methods which are accurate, sensitive and rapid
What are the advantages of standard lab testing and instrumental methods?
- standard laboratory testing
1) its available in school - instrumental methods
1) very accurate
2) sensitive and rapid
3) only small amount of sample needed
What is flame emission spectroscopy?
An example of instrumental method used to analyse metal ions in solutions
How does flame emission spectroscopy work?
The sample is put into a foame and the light given out is passed 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
What do different ions have different line spectrums?
Different ions will emit different wavelengths so each ion produces a different pattern of wavelength therefore different line spectrum
What does the intensity of the spectrum indicate?
The concentrations of that ion in the solution
