Topic 2 - states of matter and mixtures

describe the arrangement, movement and the relative energy of particles in each of the three states of matter

• the three states of matter are solid, liquid and gas

• melting and freezing take place at the melting point

  • solid → liquid: melting

  • liquid → solid: freezing

• boiling and condensing take place at the boiling point

  • liquid → gas: boiling

  • gas → liquid: condensing

• they can be represented by the simple model below, particles are represented by small solid spheres

• gas: particles have the most energy, as the particels are the most spread apart

  • liquid: particles have more energy than those in a solid, but less than those in a gas and solid have the least energy - particles vibrate in a fixed position

recall the names used for the interconversions between the three states of matter

• state changes (melting, boiling, freezing and condensing) are physical changes - they involve the forces between the particles of the substances but the particles themselves don’t change

• chemical changes are where a new product has been formed

explain the changes in arrangement, movement and energy of particles during these interconversions

• particle theory can help to explain melting, boiling, freezing and condensing…

  • the amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance

  • the nature of the particles involved depends on the type of bonding and the structure of the substance

  • the stronger the forces between the particles the higher the melting point and boiling point of the substance

predict the physical state of a substance under specified conditions, given suitable data

• if you are given the melting point and boiling point of a substance:

  • at temperature below the melting point, the substance will be solid

  • at temperatures above the melting point but below the boiling point, the substance will be liquid

  • at temperatures above the boiling point, the substance will be a gas

what is a mixture

• consists of 2 or more elements or compounds not chemically combined together

• chemical properties of each substance in the mixture are unchanged

what is a pure substance

• a pure substance = a single element or compound, not mixed with any other substance

• in everyday language, a pure substance = substance that has had nothing added to it, so it is unadulterated and in its natural state, eg. pure milk

interpret melting point data to distinguish between pure substances

• pure substances melt and boil at specific/exact temperatures, mixtures do not:

  • this means melting and boiling points data can be used to distinguish pure substances from mixtures (which melt over a range of temperatures due to them consisting of 2 or more elements or compounds)

explain the experimental technique for simple distilation

• simple distilation is used to seperate a solvent from a solution, it is useful for producing water from salt solution

  • simple distilation works because the dissolved solute has a much higher boiling point than the solvent

  • when the solution is heated, solvent vapour evaporates from the solution. the gas moves away and is cooled and condensed

  • the remaining solution becomes more concentrated in solute as the amount of solvent in it decreases

explain the experimental technique of fractional distilation for seperation of mixtures

• used to seperate a pure liquid from a mixture of liquids

  • works when the liquids have different boiling points

  • commonly used to seperate ethanol from water

  • (taking the example of ethanol) ethanol has a lower boiling point than water so it evaporates first. the ethanol vapour is the cooled and condensed inside the condenser to form a pure liquid

  • sequence of events in distilation is as follows: heating → evaporating → cooling → condensing

  • fractional distilation is also used to seperate oil. the oil is heated in the fractionating column and the oil evaporates and condenses at a number of different temperatures

  • the many hydrocarbons in crude oil can be seperated into fractions each of which contains molecules with a similar number of carbon atoms

  • the fractionating column works continuously, heated crude oil is piped in at the bottom. the vaporised oil rises up the column and the various fractions are constantly tapped off at the different levels where they condense

  • the fractions can be processed to produce fuels and feedstock for the petrochemical industry

explain the experimental technique of filtration for seperation of mixtures

• if you have produced eg. a precipitate (which is an insoluble salt), you would want to seperate the salt/precipitate from the salt soluton

  • you would do this by filtering the solution, leaving behind the precipitate on the filter paper

explain the experimental technique of crystallisation for seperation of mixtures

• if you were to have produced a soluble salt and you wanted to seperate this salt from the solution that it was dissolved in

  • you would first warm the solution in an open container, allowing the solvent to evaporate, leaving a saturated solution

  • allow this solution to cool

  • the solid will come out of the solution and crystals will start to grow, these can then be collected and allowed to dry

explain the experimental technique of paper chromatography for seperation of mixtures

• chromatography..

  • used to seperate mixtures and give information to help identify substances

  • involves a stationary phase and a mobile phase

  • seperation depends on the distribution of substances between the phases

• Rf value = distance moved by substance/distance moved by solvent

  • different compounds have different Rf values in different solvents, which can be used to help identify the compounds

  • compounds in a mixture may seperate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents

• paper chromatography

  • analytical technique separating compounds by their relative speeds in a solvent as it spreads through paper

  • the more soluble a substance is, the further up the paper it travels

  • seperates different pigments in a coloured substance

• pigment

  • solid, coloured substance

describe paper chromatography

the seperation of mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (the paper contains the stationary phase), which causes the substances to move at different rates over the paper

interpret a paper chromatogram: to distinguish between pure and impure substances, to identify substances by comparison with known substances and to identify substances by calculation and use of Rf value

• pure substances: should only have one spot on a chromatogram

• impure substances/mixtures: will show up with more than one spot on a chromatogram

• to identify by comparing with known substances: carry out paper chromatography with both the known substance and substance you’re testing on the same paper. if both spots are at the same height up the paper at the end then you know the substance you’re testing is the same as the known substance

• to identify by calculation of Rf values: you can calculate Rf values and then compare them to known values for different substances

Core practical: Investigate the composition of inks using simple distillation and paper chromatography

Aims:

• to investigate the composition of inks using simple distillation and chromatography

Simple distillation

method:

1. add a small volume of ink to a flask. connect the flask to the fractionating column and secure it with a stand, boss and clamp

2. attach a condenser to the top of the fractionating column, connect it to a cold water tap and sink, secure it over a beaker

3. heat the flask using a Bunsen burner, reducing the flame as necessary to achieve gentle simmering

4. collect a small sample of the distilled solvent, then turn the Bunsen burner off

results

1. describe the appearance of the distilled solvent

2. if your apparatus included a thermometer at the top of the column, record the maximum temperature reaches as the solvent was collected

analysis

1. explain any difference in the appearance of the solvent and ink

2. if you measured the maximum temperature, compare this to the boiling points of possible solvents. these could include water, ethanol and propanol

Paper chromatography

method:

1. draw a pencil line across the chromatography paper, 1-2 cm from the bottom

2. use a pipette or capillary tube to add small spots of each ink to the line on the paper

3. place the paper into a container with a suitable solvent in the bottom

4. allow the solvent to move through the paper, but remove the chromatogram before it reaches the top

5. allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent

results

record your results in a suitable table

analysis

1. calculate the Rf value of each spot

2. compare the Rf values and colours of each spot in the inks. describe their similarities and differences

how can waste and ground water can be made potable, including the need for sedimentation, filtration and chlorination, sea water can be made potable by using distillation and water used in analysis must not contain any dissolved salts

• potable water: it is suitable for drinking so much have:

  • low levels of microbes

  • low levels of containing substances

  • it is not the same as pure water but is still safe

• making waste and ground water potable:

  1. sedimentation: large insoluble particles will sink to the bottom of the water

  2. filtration: water is filtered through beds of sand which removes small insoluble particles

  3. chlorination: chlorine gas is put through water to kill microbes

• making sea water potable using distillation

  1. filter the seawater

  2. boil it

  3. water vapour is cooled and condensed

• water used in analysis:

  • must be pure because any dissolved salts could react with the substances you are analysing, leaving you with a false result