seperation techniques (topic 1) Flashcards
define the term ‘mixture’ (2)
- two or more different substances
- not chemically joined together
which of the diagrams above depicts a mixture of compounds
A
which two of the following substances are mixtures
- air
- steel
(for filtration)
explain why filtration cannot be used to separate a mixture of ethanol and water (1)
ethanol and water are both liquids
use the words ‘boils’, ‘cools’, ‘condenses’ and ‘water vapour’ to explain how salt water can be distilled into pure water (4)
- the salt water is heated until it boils
- water vapour leaves the solution
- water vapour travels down the condenser
- water vapour condenses in the condenser
- pure water is collected in the conical flask / beaker
suggest why it is not safe to drink the distilled water sample prepared in the school laboratory (1)
- apparatus may not have been cleaned
- risk of contamination with other chemicals in the laboratory
describe how to obtain salt crystals from salt water by crystallisation (2)
- heat the solution until crystallisation point is reached
- leave the solution to cool
hexane and water are immiscible, describe how separate samples of hexane and water can be obtained from a mixture of hexane and water (2)
- use separating funnel
- run off lower layer of liquid
explain the difference between a mixture and a compound (2)
- mixture: multiple substances mixed together, but not chemically combined/bonded
- compound: different elements together and chemically combined
suggest what would happen to the temperature of the water as it flows through the condenser (1)
- the temperature of the water increases
describe how oxygen and nitrogen are obtained from liquid air by fractional distillation (4)
- liquid air enters fractionating column
- liquid air warms
- nitrogen has a lower boiling point, so becomes a gas first, and is collected from the top of the column
- liquid oxygen has a higher boiling point, so stays in liquid state, and is collected from bottom of column
what is the name of the process used by the student
simple distillation
describe how the process shown in the image produces pure water from salt solution (4)
- the salt solution is heated
- the water evaporates
- the vapour cools in the condenser
- the vapour condenses
- pure water collects in the beaker
fractional distillation
(6)
method (max 4 marks):
- draw a start line on chromatography paper in pencil
- spot of each food colouring on pencil line
- place a suitable solvent in a beaker
- clip end of paper in water
- so chromatography paper is in the solvent but solvent is below the start line
- use a lid
- leave for water to rise up paper
- mark the solvent front
- dry the chromatography paper
measurements (max 2 marks):
- measure the distance between the start line and the centre of the spot
- measure the distance between the start line and the solvent front
- use the measurements to determine the Rf value
the Rf value of the blue dye is 0.60, the distance moved by the blue dye is 5.7 cm, calculate the distance moved by the solvent
rf value equation
which food colouring has a Rf value of 0.3
food colouring 1
from the chromatogram, what conclusions can the scientist make about the colourings in sweets S and P (3)
- S contains 6 colourings
- P contains 5 colourings
- S contains more colours than P
- both S and P contain the same 5 colourings
- both contain 1 and 3
- neither contain 2 and 4
(4)
- filter to remove the sand
- as sand is insoluble in water and salt is soluble
- distil the filtered mixture
- solid salt stays in flask and pure water condenses
