SC3 - States of Matter / Separating and Purifying Substances

Question 1

What are the 3 states of matter?

Answer 1

solid, liquid, gas

Question 2

Properties of gases

Answer 2

Particles are arranged randomly and far apart, particles move fast in all directions and can move and flow.

Question 3

Properties of liquids

Answer 3

Particles are arranged randomly and they are close together (about 50% are touching), particles roll over each other to move, liquids can flow.

Question 4

Properties of solids

Answer 4

Regular arrangement of particles, close together, particles vibrate about fixed positions, fixed volume and cannot flow.

Question 5

What are the state changes?

Answer 5

Gas -> liquid = condensation
Liquid -> solid = freezing
Solid -> liquid = melting
liquid -> gas = evaporation
Gas -> solid = deposition 
solid-> gas = sublimation

Question 6

What are the state symbols?

Answer 6

They show the state that a substance is in.

s) for solids
(g) for gases
(l) for pure liquids
(aq) for aqueous solutions (impure liquids

Question 7

What are pure substances?

Answer 7

Pure substances only contain one type of element or compound.

Question 8

What are impure substances?

Answer 8

Impure substances are mixtures, and contain more than one type of element or compound.

Question 9

How can you tell if a substance is pure or impure based on its heating or cooling curve?

Answer 9

Pure substances melt at a fixed point because all the forces between particles are the same. It will produce a flat line on a heating/cooling curve when it changes state.
Impure substances have different forces between particles, so it requires different amounts of energy to break the bonds, meaning they melt over a range of temperatures. They produce a sloped line on a heating/cooling curve when changing state.

Question 10

What is a mixture?

Answer 10

A mixture is a combination of elements and/or compounds which are not chemically joined together, and so physical processes can be used to separate them.

Question 11

What is filtration and when is it used?

Answer 11

Filtration is used when an insoluble substance is mixed with a solvent (e.g. sand and water). During filtration, a filter funnel is lined with filter paper. The solvent and any solutes pass through the filter paper to form the filtrate, which collects in a conical flask. The insoluble substances cannot fit through the holes in the filter paper and build up as residue.

Question 12

What is crystallisation and when is it used?

Answer 12

Crystallisation is used to separate dissolved solutes from their solvent. To do this, you need a Bunsen burner, a heat mat, a tripod, gauze and an evaporating dish. Pour the solution into the evaporating dish and heat on a low level until about half of the solvent has evaporated. Take the evaporating dish off the heat and leave it to cool, then dry the crystals in a oven.

Question 13

What is chromatography and when is it used?

Answer 13

Chromatography can be used to separate multiple dissolved solutes from their solvent. To do this, you need a beaker, a pencil, and some chromatography paper. Draw a line in pencil above the water line of the beaker and put your samples along it. Place the paper in the water and wait for the samples to separate into their constituents.

Question 14

What can go wrong with chromatography?

Answer 14

If start line is drawn in pen, then the ink in the pen will also separate and run up the paper, spoiling your results.
If the water line is above the start line, the samples will dissolve into the pool of water and not separate into their constituents.

Question 15

What is Rf value?

Answer 15

Rf = distance travelled by substance / distance travelled by solvent

If two substances produce the same spots on the chromatogram, it is likely that they are the same substance. Unidentified substances can also be identified by comparing Rf values of the spots to known Rf values from a book.

Question 16

What are the different phases in chromatography and why do some spots travel further than others?

Answer 16

Mobile phase = solvent
Stationary phase = chromatography paper

Substances which are more attracted to the mobile phase travel the furthest, and those which are the most attracted to the stationary phase travel the least (i.e. most soluble in the solvent travel furthest)

Question 17

What is distillation?

Answer 17

Distillation is a method for separating dissolved solids from water (i.e. it purifies the water).
You can do distillation using a Bunsen burner, tripod, conical flask, delivery tube and test tube, but this is not the most efficient method as lots of the vapour is lost. To improve this method, you can use a condenser.

Question 18

What is fractional distillation?

Answer 18

Fractional distillation is used to separate two or more liquids. Some liquids have a lower boiling point than others, so they evaporate first. You can then continue heating the flask to collect the other fractions with higher boiling points. The main difference between simple and fractional distillation is that fractional distillation uses a fractionating column, which creates a temperature gradient.

Question 19

Core practical - investigating inks

Answer 19

First the ink is place in a flask and distilled to separate the water from the ink. Then, paper chromatography is used to analyse what solutes are in ink.

Question 20

How is drinking water made potable (safe to drink)?

Answer 20

First, water from reservoirs, rivers, lakes or aquifers is passed through a sieve to remove large items such as twigs. Then, sedimentation, in which small particles are left to settle out, then filtration using beds of sand and gravel, finally, chlorination, where chlorine is added to the water to kill any microorganisms in the water.