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chemistry > experimental techniques > Flashcards

experimental techniques Flashcards

1
Q

what are the effects impurities have in pure substance

A

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

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2
Q

what are the 2 types of mixtures

A

solutions and suspensions

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3
Q

describes solutions and suspensions

A

solution: states are completely mixed, must be transparent

suspension state can be seen, not transparent

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4
Q

what is a volatile liquid

A

a liquid that evaporates easily, sign that forces between particles are weak

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5
Q

describe filtration

A

separate insoluble solid from liquid.

  1. mixtures is poured into filter funnel lined with filter paper
  2. liquid particles are small enough to go through the pores of the filter paper but solid particles are too large to go through
  3. collect the filtrate in conical flask
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6
Q

what the the method of separating a dense insoluble solid from the liquid

A

decanting

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7
Q

explain what evaporating to dryness separates

A

separate solid from liquid to obtain the solid

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8
Q

describe the technique of crystallisation

A

separate soluble solid from liquid as crystals, used for solids that can be decomposed by heat

  1. heat solution until saturated/ crystallisation point
  2. let cool down to form crystals
  3. filter to remove the liquid and obtain crystals
  4. absorb remaining liquid by pressing with a sheet of filter paper
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9
Q

how to help a solute dissolve quickly

A

heat solution

stir

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10
Q

what is aqueous solution

A

solution in water

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11
Q

what does soluble and insoluble mean

A

will dissolve in a solvent; does no dissolve in a solvent

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12
Q

define solubility

A

amount of solute that will dissolve in 100g of a solvent, at a given temp

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13
Q

define saturated solution

A

when no more of the solute will dissolve in it at that temp

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14
Q

what is solute, solvent and solution

A

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

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15
Q

what is a pure substance

A

no other substances mixed with it

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16
Q

what do you use to measure liquids and what is the unit

A

measuring cylinder, pipette, burettes

cm^3 and dm^3

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17
Q

what are disadvantages and advantages of measuring liquids using measuring cylinder, pipette and burette

A

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

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18
Q

what are the importance of pure substance

A

medicine, impurities weaken metal structure

19
Q

how to test for a saturated solution

A

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

20
Q

describe how to use simple distillation

A

separate pure liquid from a solution

  1. solution is heated in the flask until solution boils
  2. pure liquid turns into vapours and leaves the flask
  3. vapour is cooled by condenser which turns back into liquid
21
Q

what is the liquid which we obtain from distillation called?

A

distillate

22
Q

what are some safety measurements when using simple distillation

A

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

23
Q

what do we do if the distillates is volatile?

A

put the reciver in a large container of ice to keep temp of distillate low so it’ll remain in liquids state

24
Q

what shld we use if the liquid we are distilling is flammable?

A

oil or water bath

25
Q

when shld we use oil or water bath

A

oil is for liquids with a boiling point under 200 and above 100
water us for liquid that has boiling point under 100

26
Q

disadvantage of distillation saltwater ?

A

expensive as fossil fuel it main fuel

27
Q

how to be separate ethanol and water

A

use fractional distillation

  1. heat mixture in flask. at x temp, ethanol will boil. some water will evaporate. mixture of water and ethanol vapor will rise up
  2. vapours of ethanol will condense on glass beads in column , making them hot
  3. 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
  4. pure ethanol drips into the beaker
  5. eventually when thermometers reading rises above x, ethanol is gone .
28
Q

where does the water enter and leave the condenser

A

cold water enters from the bottom of the condenser and leaves from the top

29
Q

what does miscible mean

A

components that are mixed tgt

30
Q

what does fractional distillation do?

A

separate mixtures of miscible liquid with widely different boiling points

31
Q

why does fractionating column have beads

A

increase surface area so vapours can cool and condense repeatedly

32
Q

explain how to use separating funnel

A

separate immiscible liquids

  1. pour mixture into separating funnel, ensuring tap is closed
  2. support the separating funnel with retort stand, placing clean beaker below
  3. allow some time for liquids for the liquids to separate completely
  4. 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
  5. place another beaker below separating funnel and allow little liquid in the top later into it and dispose this liquid
33
Q

what do you use to separate mixtures of 2 solids of different solubility in a given solvent

A

solvent extraction/ dissolving

  1. add water into mixture
  2. stir
  3. filter the mixture and rinse the residue to remove any soluble impurity and dry it by pressing filter papers on it
  4. heat filtrate until crystallisation point
  5. allow saturated solution to cool and form crystals
  6. filter to obtain crystals
34
Q

how to separate salt and sugar

A

use solvent extraction where ethanol dissolves sugar but not salt
ethanol is flammable so use water bath

35
Q

what is fractional distillation used for in industries

A

refine crude oil into petrol and other grps of compound
separate gas in air - air is cooled until liquid then warmed up
producing ethanol

36
Q

what is sublimation

A

separate a mixture of solids, one of which sublimes

  1. heat mixture gently over bunsen burner
  2. put a evaporating dish in top of the beaker with cold water
  3. substance will evaporate then condense to from crystals
37
Q

what is the basic principle of chromatography?

A

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

38
Q

what does adsorption mean

A

the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface

39
Q

all chromatographic methods must require

A

a stationary phase - static part of solid or liquid

mobile phase - moving part- liquid or gas

40
Q

what is the set up of paper chromatography

A

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

41
Q

what is chromatography used for

A

identifying a substance
separate mixtures of substances
purify a substance by separating it from its impurities

42
Q

why do components in a mixture separate in chromatography

A

they have difference in adsorption on to the stationary phase and solubility in mobile phase

43
Q

how to calculate rf

A

distance travelled by spot / distance travelled by solvent

44
Q

what if mixtures are colourless for chromatography

A

use locating agents

locating agents binds to the chemical on spot and produce coloured spot or glows under UV light

chemistry (9 decks)

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