Topic 2 - States of matter and mixtures

Question 1

Substance A melts at -183C and boils at -50C, what state is A at -90C?

Answer 1

Liquid

Question 2

Describe the arrangement and movement of particles in solids

Answer 2

• Tightly packed together in regular arrangment
• Vibrate in fixed positions

Question 3

What are the 3 states of matter?

Answer 3

• Solid
• Liquid
• Gas

Question 4

Compare the relative energies of particles in solids, liquids and gases

Answer 4

Particles in solids have the least energy and particles in gas have most energy

Question 5

What are the names for the interconversions of state?

Answer 5

• Solid –> Liquid: Melting
• Liquid –> Solid: Freezing
• Liquid –> Gas: Evaporation
• Gas –> Liquid: Condensation

Question 6

Describe what happens when a solid is heated and melts into a liquid

Answer 6

• When heated the particles absorb thermal energy which is converted into kinetic energy causing particles in the solid to vibrate more.
• This causes slid to expand until structure breaks and becomes a liquid

Question 7

What is the difference between a physical change and a chemical change

Answer 7

• A physical change involces changes in forces between particles.
• Particles remain same and chemical properties remain same
• Chemical change affects properties of the substance

Question 8

What is it called when a solid changes straight to a gas

Answer 8

Sublimation

Question 9

Describe what happens when a liquid is heated and evaporates into gas

Answer 9

• When heated, particles in liquid expand and some particles on surface gain sufficient energy to overcome intermolecular forces and evaporate.
• At boiling point, all of liquid particles gain enough energy to evaporate

Question 10

Describe the arrangement and movement of particles in gases

Answer 10

• Well seperated with no regular arrangement
• Vibrate and move freely at high speeds

Question 11

Describe the arrangement and movement of particles in liquids

Answer 11

• Close together but able to move past each other
• Vibrate and move around each other

Question 12

What is a mixture?

Answer 12

• Substance containing 2 or more elements or compounds not chemically bonded together
• Chemical properties of each substance in mixture are unchanged

Question 13

What is a pure substance?

Answer 13

A single element or compound not mixed with any other substance

Question 14

How can you use melting point data to distinguish between pure substances and mixtures?

Answer 14

• Pure substances have sharp exact melting point whereas mixtures melt over range of temperatures since they consist of several elements/compounds

Question 15

What mixtures can be seperated using simple distillation?

Answer 15

• Used to seperate solvent from solution.
• Useful for producing water from salt solution

Question 16

What mixtures can be seperated using fractional distillation?

Answer 16

• Fractional distillation used to seperate a pure liquid from mixture of liquids
• Liquids must have different boiling points to be seperated

Question 17

How does fractional distillation work

Answer 17

• Oil heated until it evaporates into fractionating column
• Vapours rise up fractionating column and condense at different fractions, depending on relative boiling point of each substance

Question 18

What is difference between fractional and simple distillation

Answer 18

Simple distillation used to seperate solvent from solution
Fractional distillation used to seperate different liquids from mixture of liquids using their different boiling points

Question 19

What sort of mixtures can filtration be used to seperate

Answer 19

Insoluble substance from solution

Question 21

Describe how to do seperate insoluble substance from solution

Answer 21

• Place filter paper in funnel
• Pour solution containing insoluble substance through funnel into conical flask
• Insoluble substsance will collect on filter paper and solution will collect in conical flask

Filtration

Question 22

When is process of crystallisation used to seperate mixture

Answer 22

To seperate soluble solid from solution if solid decomposes when heated

Question 23

How could you seperate soluble solid from solution, if solid decomposes when heated

Answer 23

• Pour solution into evaporating dish and heat gently
• When crystals start to form, remove dish from heat and leave to cool
• Once cold, filter crystals out of solution and leave them in warm place to dry

Crystallisation

Question 24

What process can be used to identify soluble substances in mixture

Answer 24

Chromatography

Question 25

How does paper chromatography work to seperate a mixture

Answer 25

* Solvent moves through paper so anything dissolved in solvent will move up with paper * Compounds interact differently with each phase so will move different distances through paper meaning they will be seperated

Question 26

How can chromatography show composition of mixture

Answer 26

Different coloured substances in mixture will seperate as they have different solubilities in solvent and will travel at different rates

Question 27

Why should penci be used to draw line along bottom of chromatography paper

Answer 27

It will not affect experiment as it is insoluble in solvent

Question 28

Why should water (solvent) in beaker for paper chromatography be no deeper than 1cm deep

Answer 28

If it is deeper it will wash away substances placed on line on chromatography paper

Question 29

Why should you use lid when carrying out paper chromatography

Answer 29

To prevent solvent evaporating

Question 30

How many spots will pure substance produce on chromatogram? How would this be different for impure substance

Answer 30

* Pure substances produce one spot * Impure substance contains more than one compound so will produce more spots (one spot for each chemical)

Question 31

What is paper chromatography

Answer 31

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

Question 32

What is Rf value

Answer 32

Ratio between distance travelled by dissolved substance (solute) and distance travelled by solvent

Question 33

How do you calculate Rf values

Answer 33

Rf = Distance travelled by substance / Distance travelled by solvent

Question 34

When measuring distance moved by substance on chromatography paper, where should you measure between

Answer 34

Pencil base line to middle of spot of substance

Question 35

How can you use chromatography to see if certain substance is present in mixture

Answer 35

* Run pure sample of substance alongside unknown mixture * If Rf value of pure substance matches value of one of spots from mixture, it is likely present

Question 36

True or false? 'substances with higher solublility in solvent will travel further up chromatography paper'

Answer 36

TRUE, will stay dissolved in solvent (mobile phase) for longer

Question 37

How could you seperate salt from mixture of salt and sand

Answer 37

* Salt is soluble in water sand isnt * Add water to mixture * Filter solution to remove insoluble sand * Evaporate water to collect salt crystals

Question 38

How can liquids be seperated if they have different densities

Answer 38

* If liquids have different densities they will naturally seperate into two layers * Use flask with tap on bottom. Open tap to collect bottom liquid (has highest density)

Question 39

What does potable mean

Answer 39

Safe to drink

Question 40

How can waste and groundwater be made potable

Answer 40

* Sedimentation - Large insoluble particles sink to bottom after water is left still for a while * Filtration - Removes small insoluble particles by passing water through layers of sand and filters * Chlorination - Kills bacteria and microorganisms which are too small to be removed by filtration

Question 41

How can seawater be made potable

Answer 41

Distillation: * Filter to remove insoluble particles * Boik * Cool and condense water vapour