experimental techniques

Question 1

what are the effects impurities have in pure substance

Answer 1

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

Question 2

what are the 2 types of mixtures

Answer 2

solutions and suspensions

Question 3

describes solutions and suspensions

Answer 3

solution: states are completely mixed, must be transparent

suspension state can be seen, not transparent

Question 4

what is a volatile liquid

Answer 4

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

Question 5

describe filtration

Answer 5

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

Question 6

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

Answer 6

decanting

Question 7

explain what evaporating to dryness separates

Answer 7

separate solid from liquid to obtain the solid

Question 8

describe the technique of crystallisation

Answer 8

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

Question 9

how to help a solute dissolve quickly

Answer 9

heat solution

stir

Question 10

what is aqueous solution

Answer 10

solution in water

Question 11

what does soluble and insoluble mean

Answer 11

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

Question 12

define solubility

Answer 12

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

Question 13

define saturated solution

Answer 13

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

Question 14

what is solute, solvent and solution

Answer 14

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

Question 15

what is a pure substance

Answer 15

no other substances mixed with it

Question 16

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

Answer 16

measuring cylinder, pipette, burettes

cm^3 and dm^3

Question 17

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

Answer 17

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

Question 18

what are the importance of pure substance

Answer 18

medicine, impurities weaken metal structure

Question 19

how to test for a saturated solution

Answer 19

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

Question 20

describe how to use simple distillation

Answer 20

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

Question 21

what is the liquid which we obtain from distillation called?

Answer 21

distillate

Question 22

what are some safety measurements when using simple distillation

Answer 22

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

Question 23

what do we do if the distillates is volatile?

Answer 23

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

Question 24

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

Answer 24

oil or water bath

Question 25

when shld we use oil or water bath

Answer 25

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

Question 26

disadvantage of distillation saltwater ?

Answer 26

expensive as fossil fuel it main fuel

Question 27

how to be separate ethanol and water

Answer 27

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 .

Question 28

where does the water enter and leave the condenser

Answer 28

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

Question 29

what does miscible mean

Answer 29

components that are mixed tgt

Question 30

what does fractional distillation do?

Answer 30

separate mixtures of miscible liquid with widely different boiling points

Question 31

why does fractionating column have beads

Answer 31

increase surface area so vapours can cool and condense repeatedly

Question 32

explain how to use separating funnel

Answer 32

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

Question 33

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

Answer 33

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

Question 34

how to separate salt and sugar

Answer 34

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

Question 35

what is fractional distillation used for in industries

Answer 35

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

Question 36

what is sublimation

Answer 36

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

Question 37

what is the basic principle of chromatography?

Answer 37

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

Question 38

what does adsorption mean

Answer 38

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

Question 39

all chromatographic methods must require

Answer 39

a stationary phase - static part of solid or liquid | mobile phase - moving part- liquid or gas

Question 40

what is the set up of paper chromatography

Answer 40

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

Question 41

what is chromatography used for

Answer 41

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

Question 42

why do components in a mixture separate in chromatography

Answer 42

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

Question 43

how to calculate rf

Answer 43

distance travelled by spot / distance travelled by solvent

Question 44

what if mixtures are colourless for chromatography

Answer 44

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