Unit 1 & 2- States Of Matter/ Methods Of Separating And Purifying Substances Flashcards
What are the three states of matter?
Solid, liquid and gas
What is the arrangement of particles in gas?
Random and far apart
Describe the movement of particles in a gas
Fast in all directions
Describe the arrangement of particles in a liquid
Random and close together
Describe the movement of particles in a liquid
Move around each other
Describe the arrangement of particles in a solid
Regular and close together
Describe the movement of particles in a solid
Vibrate about fixed position
What type of changes of state changes?
Physical changes
What does not change during state changes
The chemical properties
What changes during a state change?
The arrangement and movement of the particles
How are particles held together in a solid?
Through many weak forces of attraction
How does a substance melt
Energy is used to overcome the forces
What happens during evaporation
The remaining attractive forces are overcome by more heat
Where does energy for melting and evaporation come from
The surroundings
What happens to the energy in particles during condensing and freezing
It is transferred from the particles to the surroundings
When is the temperature of a substance constant?
During state changes
The composition of a pure substance…
Cannot be changed and is the same in all parts of a piece of the substance
What types of substances are pure
Compounds and elements
Can pure substances be separated using physical methods?
No
What is a mixture?
A substance that contains elements and/or compounds that are not chemically bonded together
How can you separate mixtures into different substances?
Using physical processes
What does a fixed composition mean?
Any piece of the substances will have the same amount of elements in it
What are the forces holding the particles together in a solid?
Weak forces of attraction
At what point does a substance changes from a solid to a liquid?
At the melting point
Why does a pure substance have a precise melting point?
Because it has the same composition in every part of it so it’s physical properties of this same
Why do mixtures not have a precise melting point?
Because there a different compositions within the substance
How do filters separate some mixers
They let smaller pieces or liquids through but trap bigger pieces or insoluble substances
The three examples of every day filters
Cars, vacuum cleaners and air-conditioning systems
What is a solution
A mixture made of solutes (dissolved substances) in a liquid called solvent
How can solutes be separated from a solution
By evaporating the solvent and leave the solute behind
What is crystallisation
When the solvent of a solution is evaporated leaving solute separated from the solvent.
How do you sizes of crystals fairy
If the crystal form slowly the particles have longer to form an ordered pattern
What is solution mining
Water is pumped into layers of salt underground dissolving the salt in the water. The solution is then heated which evaporates leaving only the salt.
What is a saturated solution
A solution that contains the maximum amount of solvent in the amount of solute at that temperature
How can you filter solutions in a laboratory
Using a filter funnel lined with filter paper
What is the residue
Bits of insoluble substances left on the filter paper
How can crystallisation be used in the laboratory
A Bunsen burner is used to evaporate the filtrate carefully. It must not be overheated as the hot crystals spit out and can cause crystals to change chemically.
What is a hazard
Something that could cause harm
Give a hazard and solution of crystallisation
There is a risk of the solution spitting which can burn. People should wear eye protection and use a low flame to gently heat the solution
What is paper chromatography
A simple technique that is used to find out which coloured compounds the mixtures contain
Explain paper chromatography
A solvent moves along a strip of paper and carries the different substances in the mixture at different speeds so they are separated
In paper chromatography what is the mobile phase and what is the stationary phase
The mobile phase is this solute and the stationary phase is the paper
What is a chromatogram
The paper with the separate components.
What is the RF value
The distance the compound has risen divided by the distance the solvent has risen
What is the Rf value always below
1
What can paper chromatography be used for
Distinguishing pure and impure substances
Identifying substances by comparing the pattern on the chromatogram with the patterns formed by known substances
Identifying substances by calculating their Rf values.
How do you separate pure water from the dissolved solids
Distillation
Describe how distillation works
Water is evaporated which leaves the solid minerals behind. If the water vapour is then condensed it turns back into water which is now pure.
What are the two physical processes in distillation
Evaporation and condensation
Why is a condenser more efficient during distillation
It means that almost all the water vapour is condensed into water
What distillation is used to separate two or more liquids
Fractional distillation
How does fractional distillation work
The liquid mixture is heated. Different liquids will evaporate faster than others. The first fraction of collected condensated vapour has the lowest boiling point
How can fractional distillation separate to gases
The gases of cold down until they are liquid and then they are heated up slowly again
Give three uses of fractional distillation
To separate the different products in crude oil
To make alcoholic drinks such as whiskey and vodka
To separate the gases in the air
What happens in the fractional column
The hot water vapour rises but at first when is hits the cool glass it drips back down into the flask. As the column heats up there will be a temperature gradient. It will be hotter at the bottom and colour at the top. The faction with the lowest boiling point reach the top of the column first and the vapour will then pass into the condenser. If you keep heating factions with higher boiling points will then rise up the column and can be collected later.
Core practical: describe the stages of simple distillation for investigating inks
Put the ink in the flask and vapours can be led away to be condensed.
Heat the flask of ink using a Bunsen burner.
Continue heating until you have collected a few centimetres of distillate.
Note the maximum temperature obtained.
Core practical: describe the stages of paper chromatography for investigating inks
Draw a pencil line on a piece of chromatography paper about 2 cm from the bottom.
Add a small spot of ink to the pencil line
Add water to a container about 1 cm
Placed the paper into the container so the paper is supported
Take the paper out before it has reached the top and immediately mark where the solvent travelled
Calculate the Rf value
What is the process of producing pure water from the sea
Desalination
How is water separated from dissolve salts
Using simple distillation
Why is simple distillation not usually a suitable method for producing large volumes of drinking water
Because a lot of energy must be transferred to the sea
Where might they use simple distillation for desalination of large volumes
When energy resources are plentiful and cheap
Why should pure water be used for chemical experiments
Because any salts dissolved in the water can affect the results of the experiment
What does freshwater from reservoirs contain
Objects such as leaves and twigs, small and soluble particles such as grit and silt, soluble substances including salts, pesticides and fertilisers, bacteria and other organisms that may be harmful ro health.
What are the main stages of purifying drinking water
Coarse filtration, sedimentation, fine filtration, chlorination
