Topic 2 - states of matter and mixtures Flashcards
Describe the arrangement of movement of particles in solids
Tightly packed together in a regular arrangement
Vibrate in fixed positions
Describe the arrangement and movement of particles in liquids
Close together but able to move past each other
Vibrate and move around each other
Describe the arrangement and movement of particles in gases
Well separated with no regular arrangement
Vibrate and move freely at high speeds
Compare the relative Energies of particles in solids, liquids and gases
Particles in a solid have the least amount of energy and particles in a gas have the most energy
What does interconversion of state mean?
When matter changes from one state to another due to changes in temperature or pressure
What are the names for the state changes from solid to liquid and vice versa?
Solid to liquid: melting
Liquid to solid: freezing
What are the names for the state changes from liquid to gas and vice versa?
Liquid to gas: evaporation
Gas to liquid: condensation
Describe the forces between particles in solids
Strong forces of attraction between particles which keeps them in their fixed positions
Describe the forces between particles in liquids
Weaker attractive forces than in solids
Describe the forces between particles in gases
Weakest intermolecular forces so particles are in random movement
How does a physical change differ from a chemical change?
A physical change involves changes in the forces between particles. The particles themselves remain the same and the chemical properties stay the same.
A chemical change is different as it affects the chemical properties of a substance
Are physical changes relatively easy to reverse?
Yes, because no new product is formed during the changes if state
What is the term describing when a solid changes straight Into a gas?
Sublimation
Describe what happens, in terms of particles, when a solid is heated and melts into a liquid
The particles absorb thermal energy which is converted into kinetic energy. The particles in the solid vibrate more. This causes the solid to expand until the structure breaks and becomes a liquid
Describe what happens, in terms of particles, when a liquid is heated and evaporated into a gas
The particles expand and some on the surface gain sufficient energy to overcome the intermolecular forces and evaporate. At the boiling point, all of the liquid particles gain enough energy to evaporate
What is a mixture?
A substance that contains 2 or more elements or compounds that are not chemically combined together.
What is a pure substance?
A single element or compound, not mixed with any other substance
How can you use melting point data to distinguish between pure substances and mixtures?
Pure substances have a sharp exact melting point whereas mixtures melt over a range of temperature since they consist of several elements/compounds
When is simple distillation used?
To separate a pure liquid from a mixture of liquids. Only works when the liquids have different boiling points
How can ethanol be separated from water?
Simple distillation
When is fractional distillation used to separate mixtures?
To separate all the elements/compounds in a mixture.
What is the difference between fractional and simple distillation?
Simple distillation is Andy able to separate the liquid with the lowest boiling point from the mixture
Fractional distillation separates all the chemicals in a mixture, using their different boiling points
How does fractional distillation work?
Oil is heated until it evaporates into the fractionating column.
Vapours rise up the fractionating column and condense at the different fractions, depending on the relative boiling point of each substance
What sort of mixtures can filtration be used to separate?
An insoluble substance from a solution
When is the process of crystallisation used to separate a mixture?
To separate a soluble solid from a solution if the solid decomposes when heated
What process can be used to identify substances in a mixture?
Chromatography
Describe the process of crystallisation
Pour the solution into an evaporating dish and heat gently
When the crystals start to form, remove the dish from the heat and leave to cool
Once cold, filter the crystals out of the solution and leave them in a warm place to dry
Describe the process of filtration
Place filter paper in a funnel
Pour the solution containing an insoluble substance through the funnel into a conical flask
The insoluble substance will collect on the filter paper and the solution will collect in the conical flask
How does paper chromatography work to separate a mixture?
The mobile phase (solvent) moves through the stationary phase (paper) so anything dissolved in the mobile phase will move up the paper
Compounds interact differently with each phase so will move different distances through the stationary phase meaning they will be separated.
How can chromatography show the composition of a mixture?
Different coloured substances in the mixture will separate as they have different solubilities in the solvent and will travel at different rates
Why should pencil be used to draw the line along the bottom of the chromatography paper?
It will not affect the experiment as it is insoluble in the solvent
Why should the water (solvent) in the beaker for paper chromatography be no deeper then 1cm deep?
If it is deeper it will wash away the substances placed on the line on the chromatography paper
Why should you use a lid when carrying out paper chromatography?
To prevent the solvent evaporating
How many spots will a pure substance produce on a chromatogram?
Only one
How many spots will an impure substance produce on a chromatogram?
As it contains more than one compound so it will produce more spots (one spot for each chemical)
What is an Rf value?
The ratio between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent
How do you calculate arc values?
Distance travelled by substance/distance travelled by solvent
When measuring the distance moved by a substance on the chromatography paper, where should you measure between
From the pencil baseline to the middle of the spot of the substance
Will substances with a higher solubility in the solvent travel further up the chromatography paper? Why?
Yes because they will stay dissolved in the solvent for longer
How could you separate salt from a mixture of sand and salt?
Add water to the mixture
Filter the solution to remove the insoluble sand
Evaporate the water to collect the salt crystals
How can liquids be separated if they have different densities?
They will naturally sit on two layers so use a flask with a tap on the bottom. Open the tap to collect the bottom liquid
What does potable mean?
Safe to drink
How can waste and groundwater be made potable?
Sedimentation: large insoluble particles sink to the bottom after the water is left still for a while
Filtration: removes small insoluble particles by passing the water through layers of sand and filters
Chlorination: kills bacteria and microorganisms which are too small to be removed by filtration
How can see water be made potable?
Distillation
What issues surround the process of making seawater potable?
Extremely expensive as it requires a lot of energy to boil large volumes of water
Wastewater is toxic due to the high concentration of salt so must be disposed of carefully
What is deionised water?
Water that has had metallic ions (such as copper or calcium ions removed
Why is deionised water used in experimental analysis?
It is uses to prevent ions in the water interacting with the substances under analysis. If it wasn’t deionised, false positive results may be produced
