experimental techniques Flashcards
what are the effects impurities have in pure substance
increases boiling point and decreases freezing point
the more impurity there is, the bigger the change in melting and boiling points, wider the temp range over which melting and boling points occur
what are the 2 types of mixtures
solutions and suspensions
describes solutions and suspensions
solution: states are completely mixed, must be transparent
suspension state can be seen, not transparent
what is a volatile liquid
a liquid that evaporates easily, sign that forces between particles are weak
describe filtration
separate insoluble solid from liquid.
- mixtures is poured into filter funnel lined with filter paper
- liquid particles are small enough to go through the pores of the filter paper but solid particles are too large to go through
- collect the filtrate in conical flask
what the the method of separating a dense insoluble solid from the liquid
decanting
explain what evaporating to dryness separates
separate solid from liquid to obtain the solid
describe the technique of crystallisation
separate soluble solid from liquid as crystals, used for solids that can be decomposed by heat
- heat solution until saturated/ crystallisation point
- let cool down to form crystals
- filter to remove the liquid and obtain crystals
- absorb remaining liquid by pressing with a sheet of filter paper
how to help a solute dissolve quickly
heat solution
stir
what is aqueous solution
solution in water
what does soluble and insoluble mean
will dissolve in a solvent; does no dissolve in a solvent
define solubility
amount of solute that will dissolve in 100g of a solvent, at a given temp
define saturated solution
when no more of the solute will dissolve in it at that temp
what is solute, solvent and solution
substance you dissolve in the solvent to make a solution; liquid in which solute is dissolved, to make a solution; mixture obtained when a solute is dissolved in a solvent
what is a pure substance
no other substances mixed with it
what do you use to measure liquids and what is the unit
measuring cylinder, pipette, burettes
cm^3 and dm^3
what are disadvantages and advantages of measuring liquids using measuring cylinder, pipette and burette
measuring cylinder is less accurate where there’s no d.p but fast to used
pipette and burette is more accurate nut harder to used
what are the importance of pure substance
medicine, impurities weaken metal structure
how to test for a saturated solution
take a clean glass rod and dip into the solution and remove it.
there wld be a small amount if solution on the rod
if small crystals form on the rod as the solution cools, the solutions is saturated
describe how to use simple distillation
separate pure liquid from a solution
- solution is heated in the flask until solution boils
- pure liquid turns into vapours and leaves the flask
- vapour is cooled by condenser which turns back into liquid
what is the liquid which we obtain from distillation called?
distillate
what are some safety measurements when using simple distillation
thermometer needs to be placed at side arm of distillation flask to measure boiling point and not the substance that is being distilled
boiling chips ensure smooth boiling
don’t use Bunsen burners with flammable liquid
what do we do if the distillates is volatile?
put the reciver in a large container of ice to keep temp of distillate low so it’ll remain in liquids state
what shld we use if the liquid we are distilling is flammable?
oil or water bath
when shld we use oil or water bath
oil is for liquids with a boiling point under 200 and above 100
water us for liquid that has boiling point under 100
disadvantage of distillation saltwater ?
expensive as fossil fuel it main fuel
how to be separate ethanol and water
use fractional distillation
- heat mixture in flask. at x temp, ethanol will boil. some water will evaporate. mixture of water and ethanol vapor will rise up
- vapours of ethanol will condense on glass beads in column , making them hot
- when bead reach x temp, ethanol vapour will no longer condense. only the water vapour will- water drips back into flask and ethanol vapour goes into condenser
- pure ethanol drips into the beaker
- eventually when thermometers reading rises above x, ethanol is gone .
where does the water enter and leave the condenser
cold water enters from the bottom of the condenser and leaves from the top
what does miscible mean
components that are mixed tgt
what does fractional distillation do?
separate mixtures of miscible liquid with widely different boiling points
why does fractionating column have beads
increase surface area so vapours can cool and condense repeatedly
explain how to use separating funnel
separate immiscible liquids
- pour mixture into separating funnel, ensuring tap is closed
- support the separating funnel with retort stand, placing clean beaker below
- allow some time for liquids for the liquids to separate completely
- open tap to allow the denser liquid at the bottom to drain into the beaker
* *remeber to close the tap before liquid in the top layer ruins out - place another beaker below separating funnel and allow little liquid in the top later into it and dispose this liquid
what do you use to separate mixtures of 2 solids of different solubility in a given solvent
solvent extraction/ dissolving
- add water into mixture
- stir
- filter the mixture and rinse the residue to remove any soluble impurity and dry it by pressing filter papers on it
- heat filtrate until crystallisation point
- allow saturated solution to cool and form crystals
- filter to obtain crystals
how to separate salt and sugar
use solvent extraction where ethanol dissolves sugar but not salt
ethanol is flammable so use water bath
what is fractional distillation used for in industries
refine crude oil into petrol and other grps of compound
separate gas in air - air is cooled until liquid then warmed up
producing ethanol
what is sublimation
separate a mixture of solids, one of which sublimes
- heat mixture gently over bunsen burner
- put a evaporating dish in top of the beaker with cold water
- substance will evaporate then condense to from crystals
what is the basic principle of chromatography?
components in a mixture have different tendencies to absorb onto a surface and dissolve in a solvent
different solubilities in a given solvent - more soluble a substance, the further it will travel
what does adsorption mean
the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface
all chromatographic methods must require
a stationary phase - static part of solid or liquid
mobile phase - moving part- liquid or gas
what is the set up of paper chromatography
1.draw pencil line across width of paper, abt 1 cm from bottom - base line
2. place concentrated solutions of mixture on middle section on pencil line using capillary tube
3. hang strip in a beaker / glass containing solvent
solvent shld be below base line
what is chromatography used for
identifying a substance
separate mixtures of substances
purify a substance by separating it from its impurities
why do components in a mixture separate in chromatography
they have difference in adsorption on to the stationary phase and solubility in mobile phase
how to calculate rf
distance travelled by spot / distance travelled by solvent
what if mixtures are colourless for chromatography
use locating agents
locating agents binds to the chemical on spot and produce coloured spot or glows under UV light
