chapter 3: separation and purification Flashcards
what is a mixture?
a mixture is made up of two or more substances that are not chemically combined
what is a pure substance?
- it is made up of a single element or a compound and is not fixed with any other substances
what is filtration used for? and how does it work?
- used to separate insoluble solid particles from a liquid
> can do so because the liquid particles are small enough to pass through the pores of the filter paper but a solid cannot - solid that remains on the filter paper is called the residue and the liquid that passes through is called the filtrate
what is evaporation to dryness used for?
- used to obtain a soluble solid ( thermally stable) from a solution by heating the solution until all the water has boiled off
- solid obtain by evaporation to dryness is not always pure
> when all the water has been removed, any soluble impurities will be left together with the solid
what is crystallisation and what is it used for?
- obtaining a pure, soluble solid (thermally unstable) sample from a solution
- water is removed by heating the solution and heating is stopped when a saturated solution is formed
- if the resulting solution is allowed to cool to room temp
> dissolved solid crystal will form pure crystals - crystals are the rinsed with cold distilled water to remove water soluble impurities
> blot dry between two sheets of filter paper
what is sublimation used to separate? and what are some examples?
- it is used for separating a solid that sublimes from one that does not
- eg. iodine, carbon dioxide, ammonium chloride
what is using a magnet for and what are some example of metals that are magnetic?
- used to separate a magnetic substance from a non magnetic substance
- eg. iron, nickle, cobalt
what is simple distillation used for?
- used to separate a pure solvent from a soluble solute in a solution
fill in the blanks on the steps of simple distillation:
- in distillation flask, solution boils
> __i__ added to ensure ___ii__ boiling
> water __iii__, rises and enters the _iv___ - in the condenser, water vapour is cooled
> vapour condenses and cooled into __i__ water - pure water collected as a __i__ in the conical flask
- remaining salt solution becomes concentrated
> if distillation allowed to carry on, a solid residue of salt will be left in the flask
1i) boiling chips
1 ii)smooth
1 iii)vapourises
1 iv) condenser
2i) pure
3i) distillate
distillation:
why should the bulb of the thermometer be placed beside the side arm of the distillation flask and not inside the solution?
- ensures that the thermometer is measuring the boiling point of the substance being distilled .
what is the separating funnel used for?
it is used for separating immiscible liquids
what needs to be done for a volatile liquid to be distilled and why?
- if distillate is volatile, the receiver can be put into a large container filled with ice
> helps keep the temperature of the distillate low so that it remains in a liquid state
how does the temperature change as salt solution undergoes distillation?
-when the salt solution is heated, the temperature increases
- when solution boils > thermometer records a temperature of 100°C which is the temperature of the steam
>temperature remains unchanged until all the water has boiled off
what is fractional distillation used for? and give an example
- used to separate two miscible liquids with different boiling points
eg. ethanol and water
what are industrial applications of fractional distillation?
- obtain nitrogen, argon and oxygen from air
- separate petroleum into useful fractions
- obtain ethanol produced by the fermentation of glucose solution
what is chromatography used for? and what is a chromatography paper with the separated components called?
- a method of separating components of a mixture that dissolves in the solvent
- chromatogram
what does Rf value stand for?
- retention factor
just remember this :)
- when chromatography is allowed to proceed for a short time and a longer time, Rf value is obtained
- Rf value of substance does not change as long as chromatography is carried out under the same conditions
tehe patrick dempsey is hot
what happens if we need to run a chromatogram on colourless substances such as amino acids?
we spray a locating agent
> causes colourless substances to become coloured spots
what are the uses of chromatography?
- separate the components in a sample
> dyes in ink, pigments in plants and amino acids obtained from plants - identify components present in a sample
>traces of banned substances in food - identify substances
> poisons pesticides and drugs - determine whether a sample is pure
how to determine if a solid is pure?
- if it has an exact and fixed melting point
what are the effects of impurities on melting point?
- impurities lowers the melting point of a solid
>greater amount of impurities, the lower the melting point - cause melting point to take place over a range of temperature
what are the effects of impurities on boiling point?
- increases the boiling point of a liquid
> the greater amount of impurities, the higher the boiling point - also causes boiling point to take over a range of temperatures.
describe the process and the steps of separating immiscible liquids using the separating funnel. use oil and water for your explanation.
- *make sure that the tap of it is closed
pour the mixture of oil and water into the separating funnel - support the separating funnel using the retort stand and place a clean beaker below the separating funnel
- allow liquids to separate completely ( may take some time)
> denser liquid (water) will be the bottom layer - open the tap of the funnel & allow the bottom layer to drain into the beaker
> close tap before top layer liquid runs out - place another beaker below the separating funnel and open the tap and allow a little of the top layer of liquid into the beaker > dispose it
> funnel contains oil and beaker contains water
