C4 Chemical Changes

Question 1

Examples of pH’s

Answer 1

pH 0-1 stomach acid
2 - vinegar or lemon juice 
4 acid rain 
6 normal rain 
8 washing up liquid 
10 pancreatic juice 
11 bleach

Question 2

What is an indicator

Answer 2

Dye that changes colour depending on whether it’s above or below a certain pH
Wide range indicators have many dyes - gradually change

Question 3

What is an acid

Answer 3

A substance that forms an aqueous solution with a pH less than 7

Question 4

What’s a base

Answer 4

Substance with pH greater than 7

Question 5

Chemical reaction for neutralisation

Answer 5

Acid + base -> salt + water

Question 6

What happens when an acid neutralises a base

Answer 6

All products are neutral

Question 7

What do acids produce in water

Answer 7

Produce protons - they ionise in aqueous solution and produce hydrogen ions
H+ ion is a proton

Question 8

What’s a strong acid

Answer 8

Strong acids ionise completely in water - acid particles dissociate to release H+ ions (sulphuric, hydrochloric and nitric

Question 9

What are weak acids

Answer 9

Weak acids (ethnicm citric and carbonic) don’t fully ionise in water - only small proportion dissociates to form H+ ions 
Ionisation of a weak acid is a reversible reaction - equilibrium between undissociated and dissociated acid. As there’s only a few H+ ions, equilibrium lies left

Question 10

Why are strong acids more reactive

Answer 10

As the concentration of H+ ions is higher, rate of reaction is quicker

Question 11

What is pH a measure of

Answer 11

Measure of concentration of H+ ions
Every decrease of pH 1 - concentration of H+ ions increase by factor of 10
pH 4 has 10x concentration of H+ ions than pH 5
Decrease by 2 - H+ increase by factor of 100

Question 12

What is acid strength

Answer 12

Tells you what proportion of acid molecules ionise in water

Question 13

What does concentration measure of acid

Answer 13

How much acid there is in a certain volume of water

pH decreases with increasing concentration no matter the strength

Question 14

What are metal oxides and hydroxides

Answer 14

They’re bases that sometimes dissolve in water and these soluble compounds are alkalis

Question 15

Chemical Reaction for acids and metal oxides or acids and hydroxides

Answer 15

Acid + metal oxide -> salt + water

Acid + hydroxide -> salt + water

Question 16

What does the salt produced depend on

Answer 16

Depends on acid and metal ion
E.g
Hydrochloric acid + copper oxide -> copper chloride + water

Question 17

Acid and what produces CO2

Answer 17

Acid and metal carbonates produce CO2

Metal carbonates are also bases

Question 18

Chemical reaction for acids and metal carbonates

Answer 18

Acid + metal carbonates -> salt + water + carbon dioxide
E.g
Sulphuric acid + calcium carbonate -> sulphuric carbonate + water + carbon dioxide

Question 19

What can you make soluble salts with

Answer 19

Insoluble bases -> need to pick right acid and insoluble base - like insoluble metal oxide, hydroxide or carbonate
Warm dilute acid
Add insoluble base bit by bit until no more reacts - neutralised = solid sinks
Filter excess solid
Gently heat with water + let cool- salt crystals should form - filtered from solution and dried - crystallisation

Question 20

What is reactivity based off of

Answer 20

How easily an atom looses electrons and forms ions

Higher up in reactivity series = more easily they form positive ions

Question 21

List the reactivity series from most to least

Answer 21

Potassium, sodium , lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper

Question 22

Metals also react with water - chemical reaction

Answer 22

Metal + water -> metal hydroxide + hydrogen

Question 23

Speed of reaction is indicated by rate at which…

Answer 23

Bubbles of hydrogen are given off

More reactive metal = faster reaction

Question 24

Lots of metals react with oxygen to form…

Answer 24

Oxides through oxidation.

Question 25

What are Oxides often

Answer 25

Often ores that metals need to be extracted from

Question 26

What’s a reduction reaction

Answer 26

Separate metal from oxide

Question 27

Formation of metal ore

Answer 27

Oxidation = gain of oxygen

Question 28

Extraction of metal

Answer 28

Reduction = loss of oxygen

Question 29

Some metals can be extracted by....

Answer 29

Reduction with carbon | Some metals extracted from ores chemically by reduction using carbon

Question 30

What happens during reduction using carbon

Answer 30

Ore is reduced as oxygen is removed from it, and carbon is oxidised E.g Iron(III)Oxide + Carbon -> iron + carbon dioxide

Question 31

How can metals higher than carbon be extracted

Answer 31

Extracted with electrolysis

Question 32

How can metals below carbon be extracted

Answer 32

Reduction by carbon - as carbon can only take away oxygen from metals less reactive than itself > displacement

Question 33

Why is gold mined in its elemental form

Answer 33

Some metals are so unreactive so they are in earth as the metal itself

Question 34

What’s a redox reaction

Answer 34

If electrons are transferred, it’s a redox reaction

Question 35

What is OIL RIG

Answer 35

oxidation is loss (of electrons) Reduction is gain (of electrons) Oxidation and reduction also used in terms of oxygen

Question 36

REduction and OXidation Happen...

Answer 36

At the same time > RED-OX

Question 37

Displacement reactions are...

Answer 37

Redox reactions

Question 38

What do displacement reactions involve

Answer 38

Involve one metal kicking the other out - > more reactive metal will displace the less reactive metal from its compound E.g iron + copper Sulfate -> iron Sulfate + copper Iron looses 2 electrons - oxidised Copper gains two to become Copper atom - reduced

Question 39

What are ionic equations

Answer 39

Show useful bits of reactions

Question 40

What’s in an ionic equation

Answer 40

Contains only the particles that react are shown | E.g the displacement but not the stuff that doesn’t change

Question 41

What is electrolysis

Answer 41

Splitting up of electricity

Question 42

What happens during electrolysis

Answer 42

An electric current is passed through an electrolyte Ions move towards electrodes where they react and the compound decomposes Positive ions in electrolyte will move toward the cathode (-ve electrode) and gain electrons Negative ions will move toward anode (+ve electrode) and lose electrons Creates flow of charge through electrolyte as ions travel to electrodes As ions gain/lose electrons they form uncharged elements and are discharged from the electrolyte

Question 43

What’s an electrolyte

Answer 43

Liquid of solution which can conduct electricity

Question 44

What’s an electrode

Answer 44

Solid that conducts electricity and is submerged in electrolyte

Question 45

What does electrolysis of molten ionic solids form

Answer 45

Forms elements An ionic solid can’t be electrolysed because ions in fixed positions and can’t move Molten ionic compounds can be electrolysed as ions can move freely and conduct electricity Molten ionic liquid e.g lead bromide are always broken up into their elements Positive metal ions reduce to element at cathode Negative non-metal ions oxidised to element at anode

Question 46

How can metals be extracted from ores with electrolysis

Answer 46

Method is very expensive as lots of energy required to melt ore and produce required current 1. Aluminium extracted from bauxite by electrolysis 2. Aluminium oxide has high melting point - mixed with cryolite to lower point 3. Molten mixture contains free ions - conductor 4. Positive Al3+ Ions attracted to negative electrode where they pick up 3 electrons and turn into neutral aluminium atoms - sink to bottom of tank 5. Negative O2- ions attracted to anode and loses 2 electrons -> neutral oxygen atoms combine to form O2 molecules Aluminium -> Aluminium + oxygen oxide At cathode Al3+ + 3e- —> Al At anode 2O2- —> O2 + 4e-

Question 47

What happens during electrolysis of aqueous solutions

Answer 47

In aqueous solutions, there is H+ and OH- ions from water At cathode if H+ ions present > hydrogen gas produced if the metal forms an elemental metal that is more reactive than hydrogen If metal ions form elemental metal that is less reactive than hydrogen -> solid layer of pure metal produced At anode if OH- and halide ions(Cl-, Br-, I-) present, molecules of chlorine, bromine or iodine are formed. No halide ions - OH- ions discharged and oxygen formed Examples on C4 loose sheet