Topic 0- Alchemy and potions

Question 1

what is the conversion of a solid to a liquid?

Answer 1

melting. particles gain kinetic energy and vibrate faster and faster. This allows particles to overcome forces or attraction that holds them in place in the state of a solid. The regular pattern is broken down and the particles are free to ‘slide over’ to each other

Question 2

what is the conversion of a liquid to a solid?

Answer 2

freezing. the particles lose kinetic energy and this allows the forces of attraction between the particles to hold them together. The particles arrange themselves into a regular pattern and cannot slide over each other

Question 3

what is the conversion of a liquid to a gas?

Answer 3

boiling. the particles gain kinetic energy and move further apart. Eventually the forces of attraction between the particles are completely destroyed and are then able to escape from the liquid

Question 4

what is the conversion of a gas to a liquid?

Answer 4

condensing. the particles lose kinetic energy and this allows the forces of attraction to bring the particles closer together. The particles eventually clump together to form a liquid

Question 5

what is the conversion of a solid to a gas?

Answer 5

sublimation. the particles gain kinetic energy and vibrate faster and faster. Eventually the forces of attraction between particles are completely broken and they are able to escape from the solid

Question 6

what are forces of attraction?

Answer 6

also known as intermolecular forces they are the forces which mediate interaction between molecules

Question 7

describe an experiment to investigate the small size of particles and their movement (dilution of coloured solution)

Answer 7

when potassium manganate crystals are dissolved in water, a purple solution is formed. Very few tiny crystals can produce a highly intense colour. When this solution is diluted several times, the colour fades, but does not disappear until a lot of dilutions are made. This indicates that there are a large number of particles of potassium manganate in a very small amount of solid. If this is true, then the particles of potassium manganate must be very tiny.

Question 8

describe an experiment to investigate the small size of particles and their movement (diffusion)

Answer 8

particles will move to fill the space available to them. They can do this in both liquids and gases. Place hydrochloric acid at one end of a tube and ammonia solution at the other. Where they meet a ring of ammonium chloride appears. From this we can tell that the ammonium must have travelled faster, as it got further in the time. Lighter particles travel faster, so we can tell that ammonia is a lighter gas

Question 9

what is meant by the term ‘atom’?

Answer 9

atoms are made up of sub-atomic particles called protons, neutrons and electrons

Question 10

what is meant by the term ‘molecule’?

Answer 10

most molecules are made up of two or more atoms covalently bonded together. Molecules that contain only one atom are called monatomic molecules

Question 11

what are elements?

Answer 11

a substance made up of just one type of atom

Question 12

what are compounds?

Answer 12

a molecule that is made up of atoms of 2 or more different kind of elements

Question 13

what are mixtures?

Answer 13

two or more atoms or molecules that are mixed together but not actually chemically bonded to each other

Question 14

describe experimental techniques for the separation of mixtures (filtration)

Answer 14

Used to separate two substances: one solid, one liquid
this consists of a barrier which one component of a mixture can pass through but the other is caught by eg. water goes through filter paper, rocks are caught by it

Question 15

describe experimental techniques for the separation of mixtures (simple distillation)

Answer 15

used to separate mixtures of a liquid and a soluble solid
one substance is evaporated off. eg. salt water is heated to 100°; water evaporates off (it rises and then goes down into the condenser where it is cooled back into water), the salt is left in the original flask

Question 16

describe experimental techniques for the separation of mixtures (crystallisation)

Answer 16

used to create pure crystals of a solid that have been dissolved in a solvent
a solution is warmed allowing the solvent to evaporate, the solution is now left to cool and will form crystals

Question 17

describe experimental techniques for the separation of mixtures (fractional distillation)

Answer 17

the mixture is evaporated and rises up the tube. Different substances have different boiling points and so will condense at different temperatures; as the mixture travels up the tube, the temperature decreases, substances begin to condense at different places (due to the change in temperature) and are collected. This separates the mixture into its different parts

Question 18

describe experimental techniques for the separation of mixtures (paper chromatography)

Answer 18

used to see the different dyes in a substance or to separate them

• paper with a pencil line and a dot of substance A is put into a beaker of solvent
• paper must not be dipped in further than pencil line
• the solvent will travel up the paper
• the dyes will (usually) separate travelling up the paper
• the further away from the line, the more soluble the dye (due to particle size)
• if substance A does not separate, it is ether pure or not soluble in the solvent

Question 19

what is meant by soluble?

Answer 19

able to be dissolved, especially in water

Question 20

how can information from chromatograms be used to identify the composition of a mixture?

Answer 20

• some coloured substances are better at dissolving in liquid than bonding with paper; so they travel further up the paper
• if two substances travel the same distance up the paper, they’re likely to be the same substance (eg. same colour)
• the shape on the chromatogram can be compared with that of known substances and where they match they are the same substance

Question 21

how do you calculate rf value?

Answer 21

distance moved by spot/ distance moved by solvent front (never more than 1)

Question 22

what does the rf value tell us?

Answer 22

the higher the rf value, the higher the spot

Question 23

what are the uses of chromatography?

Answer 23

• to determine the purity of a given substance
• to identify poisons and drugs, or to detect traces of unlawful dyes or other additives in foodstuffs
• to separate pigments from plants, dyes from ink, amino acids from proteins