Topic 2 - States of Matter & Mixtures

density of solid

high

density of liquid

medium

density of gas

low

arrangement of particles in a solid

regular lattice

arrangement of particles in a liquid

randomly arranged

arrangement of particles in a gas

randomly arranged

movement of particles in a solid

vibrate around a fixed position

movement of particles in a liquid

move around and past each other

movement of particles in a gas

move rapidly and randomly in all directions

ranking of states of matter from lowest energy to highest per particle

solid

liquid

gas

What happens during a change of state from solid to liquid and liquid to gas

When the melting/boiling point is reached, then energy is used to break the attractive forces between the particles instead of increasing the mean particles’ energy

melting

solid to liquid

boiling

liquid to gas(from below surface as well as on surface)

freezing

liquid to a solid

evaporation

liquid to a gas(at surface only)

condensation

gas to a liquid

sublimation

solid to a gas

deposition

gas to solid

What type of change is a change of state of matter?

physical change

Explain the change in arrangement from solid to liquid

The regular lattice arrangement of a solid is broken and now there is a random arrangement. However, the particles are still touching due to existing but weaker forces of attraction

Explain the change in energy from solid to liquid

The mean energy per particle increases due to the solid being heated up

Explain the change in particle movement from solid to liquid

the particles go from vibrating in their fixed positions to being able to move past each other

Explain the change in particle arrangement from liquid to gas

The particles go from being able to touch each other to being completely separate from each other, this is due to the attractive forces between the particles being completely broken

Explain the change in particle movement from liquid to gas

the particles go from moving past each other to flying around the container in a rapid and random motion

Explain the change in particle energy from liquid to gas

the mean energy has increased per particle, thus the energy is at its highest in a gas

How does condensation work?

When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid

When does evaporation only happen?

Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquids surface at low temperatures, below the boiling point of the liquid

What 2 factors affect how quickly a liquid can evaporate?

The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate

Does evaporation occur at one specific temperature?

No, evaporation occurs over a range of temperatures, but heating will speed up the process as particles need energy to escape from the surface

label this diagram

A - solid
B - transitioning from solid to liquid
C - liquid
D - transitioning from liquid to gas
E - gas
F - increasing the temperature and speed of the particles in a gas

How to work out substance state of matter given temperature, bp and mp

mp > temp> bp - liquid
temp <= mp - solid
temp >= bp - gas

Why do u suppose condensing and freezing plateau?

Energy is being absorbed to create attractive forces between the particles

pure substance

consists of a single element/compound and contains no other substances

mixture

2 or more elements that are physically but not chemically mixed together.

The chemical properties of the substances in a mixture remain unchanged

What’s the difference between mps and bps in pure substances vs mixtures?

mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the mp and broaden the mp range

pure substances melt and boil at sharp and specific temperatures

How do you test the purity of drugs?

Slowly heat up a small amount of the sample which makes it easier to observe the exact melting point. This is then compared to data tables and the closer the measured value is to the actual mp/bp then the purer the sample is

What does an impure substance look like on a cooling curve

An impure sample of the compound would produce a gradual decrease in temperature as it freezes as shown in the graph below

What does a pure substance look like on a cooling curve

The horizontal part of the graph shows that the compound has a sharp melting point, so the compound is pure

What is simple distillation used for?

To separate a liquid and soluble solid from a solution

Why does simple distillation work?

Because there is a difference in boiling points

Label the apparatus for distillation

A - round bottom flask
B - a heat source, usually a Bunsen Burner
C - evaporated solvent
D - condenser with condensing jackets(water going out at the top and water coming in at the bottom)
E - distillate

Describe the stages of simple distillation

Stage 1 - Set up equipment.

Stage 2 - Place and heat the mixture in a distillation flask.

Stage 3 - The liquid will boil to become a gas.

Stage 4 - As the solvent vapourises, it rises up and leaves the solute behind

Stage 5 - The vapourised solvent enters the condenser

Stage 6 - The cold water around the condenser will make the steam condense back into liquid form.

Stage 7 - Collect the distillate

miscible

Describes two or more liquids that are completely soluble in each other

What is fractional distillation used for?

two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two)

What is a fractionating column?

A vertical column used in fractional distillation to separate liquids based on their boiling points.

How does a fractionating column work?

The lower melting point liquid rises to the top while the higher melting point liquid sinks, due to multiple condensers at different levels cooling the vapors at different rates.

What is simple distillation weak in that fractional distillation excels in?

Separating components of mixtures with similar boiling points

anti-bumping granules

Added to the round bottomed flask during distillation to spread the heat

Uses of fractional distillation in real life

separate crude oil
make alcoholic drinks such as vodka and whisky, hence the name a brewing distillery
separate elements of air

What is filtration used for?

to separate an undissolved solid from a mixtures of the solid and a liquid/ solution

How does filtration work?

A piece of filter paper is placed in a filter funnel above a beaker

A mixture of insoluble solid and liquid is poured into the filter funnel

The filter paper will only allow small liquid particles to pass through as filtrate

Solid particles are too large to pass through the filter paper so will stay behind as a residue

filtrate

the liquid that passes through the filter paper in filtration

residue

Solid left in the filter paper after filtration

solubility

a measure of how much solute can dissolve in a given solvent at a given temperature.

Why might we crush the solute to increase solubility?

When a substance dissolves, its particles are broken apart by the solvent particles, if we crush the solute then the solvent has less work to do

solubility factors

surface area, agitation(moving the solute to improve contact with the solvent particles), temperature, pressure

What is crystallisation used for?

Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water)

How are solute crystals obtained via crystallisation?

The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind

Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution

If the solution is saturated, crystals will form on the glass rod

The saturated solution is allowed to cool slowly

Crystals begin to grow as solids will come out of solution due to decreasing solubility

The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry

What is paper chromatography used for?

to separate substances that have different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink)

What is a pencil line used for in paper chromatography?

To place spots of the sample on it

Why is a pencil line used on chromatography paper?

Pencil is used for this as ink would run into the chromatogram along with the samples

Why does the pencil line need to sit above the solvent level?

so the samples don’t wash into the solvent container

How does the solvent travel up the paper?

Via capillary action, basically it moves up even with gravity acting on it

Why will the substances spread apart in chromatography?

Different substances have different solubilities so will travel at different rates, causing the substances to spread apart

Which substances spread the furtthest?

Those substances with higher solubility will travel further than the others

What would pure substances look like on a chromatogram?

Pure substances will produce only one spot on the chromatogram

What would mixtures and impure substances look like on a chromatogram?

If the substance is a mixture, it will separate on the paper to show all the different components as separate spots

An impure substance therefore will produce a chromatogram with more than one spot

What will 2 identical substances look like on a chromatogram?

Both chromatograms produced will be identical

What are R_f (retention values) used for?

To identify the components of mixtures by comparing the Rf values of unknown substances in chromatography to substances with known Rfs to see if they match in Rf value

Rf value equation

distance travelled by substance ÷ distance travelled by solvent

What is the scale of Rf values?

0-1

What can be said about a substance with an Rf value close to 1?

the closer it is to 1, the more soluble is that component in the solvent

CP: Investigating Inks - separating the inks

Ink consists of a solvent which has different dyes dissolved in it

The investigation must thus include analysis of both the solvent and the dyes used

The solvent must first be separated which can be done by simple distillation

Solvents tend to have low boiling points than the dyes which tend to be more viscous so it will evaporate first.

Add anti-bumping granules and heat gently so as not to go past the boiling point

Record the temperature of boiling point

CP: Investigating Inks - paper chromatography materials

A 250 cm3 beaker

A wooden spill

A rectangle of chromatography paper

Four known food colourings labelled A–D

An unknown mixture of food colourings labelled U

Five glass capillary tubes

Paper clip

Ruler & pencil

CP: Investigating Inks - Method of chromatography

1. Use a ruler to draw a horizontal pencil line 2 cm from the end of the chromatography paper

2. Use a different capillary tube to put a tiny spot of each colouring A, B, C and D on the line

3. Use the fifth tube to put a small spot of the unknown mixture U on the line

4. Make sure each spot is no more than 2-3 mm in diameter and label each spot in pencil

5. Pour water into the beaker to a depth of no more than 1 cm and clip the top of the chromatography paper to the wooden spill. The top end is the furthest from the spots

6. Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper

   should dip into the solvent

7. Allow the solvent to travel undisturbed at least three quarters of the way up the paper

8. Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line

9. Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent

10. For each of food colour A, B, C and D measure the distance in mm from the start line to the middle of the spot

The R_f values of food colours A, B, C and D should be compared to that for the unknown sample as well as a visual comparison being made

In the UK, where is drinking water sourced from?

rivers

lakes

underground aquifers

potable water

water that is safe to drink

What happens to water in screening and sedimentation?

Water first passes through a sieve to remove large debris

In sedimentation, larger insoluble particles sink to the bottom

In sedimentation, why might chemicals such as iron sulfate or aluminium sulfate be added?

To help smaller particles clump together and settle

What happens in water filtration?

Water is filtered through beds of sand and gravel to remove remaining small solid particles

What happens in water chlorination?

Chlorine is added to kill harmful bacteria and other microorganisms that can’t be removed by filtration.

This helps prevent diseases such as cholera or typhoid

How do you make sea water potable?

Since it contains mainly salts, simple distillation can be used to separate the water and the salts

Why is making seawater potable expensive?

Lots of energy is required to heat the large volumes of water to 100 degrees Celsius

What must happen to the wastewater produced in making seawater potable?

It must be disposed of correctly as the wastewater is extremely toxic due to the very high concentration of salts.

deionised water

water that has had metallic ions such as calcium or copper removed

How does water deionisation work?

Deionisation uses specifically designed ion-exchange resins that remove ions by exchange with hydrogen and hydroxide ions in water, which then recombine to form water molecules

Why is deionised water used in chemical investigations

Deionised water is used as the ions could react with the substances under analysis and would give the experiment a false result