Chemical Changes.5

Question 1

Properties of acids

Answer 1

pH of aqueous solutions is less than 7

Source of hydrogen ions
H+ (aq) in solution

Hydrochloride acid releases H+ ions:
HCL (aq) -> H+ (aq). + Cl- (aq)

Ethanoic

Question 2

What is electrolysis used for

Answer 2

To decompose ionic compounds in the molten state or dissolved in water

Question 3

Electrolyte

Answer 3

Ionic compound in the molten state (liquid) or dissolved in water

Question 4

Electrolysis is

Answer 4

A process in which electrical energy from a direct current (dc) supply, decomposes an electrolyte

Question 5

Anions are

Answer 5

Negatively charged ions that move to the positive electrode (anode)

Question 6

Cations are

Answer 6

Positively charged ions that life to the negative electrode (cathode)

Question 7

Moving charges

Answer 7

The ions in an electrolyte are charged particles. An electric current will pass through the electrolyte only if the ions are free to move from place to place

Question 8

Remember that ions :

Answer 8

Can move about in liquids and solutions

Cannot move about in solids

Question 9

Ions in a solution

Answer 9

Water is a covalent compound some of its molecules naturally form ions

H2O (l) reversible H+(aq) + OH-(aq)

Question 10

Presence of these ions means that a solution of an ionic compound contains

Answer 10

Cations and anions from the dissolved ionic compound and

H+ and OH- ions from the water

Question 11

Competing ions

Answer 11

During electrolysis of an aqueous solution all the ions in the electrolyte compete to be discharged and from products

1- hydrogen gas is produced if H+ ions are discharged: 2H+ (aq) + 2e- -> H2 (g)

2- oxygen gas is produced if OH- ions are discharged: 4OH- (aq) -> 2H2O (l) + O2 (g) + 4e -

Question 12

What happens st the cathode

Answer 12

Negative electrode:
Hydrogen is produced unless the compound contains ions from a metal less reactive than hydrogen
In that case
The metal is produced instead

Question 13

What happens at the anode

Answer 13

The positive electrode:

Oxygen is produced from OH- ions unless 
The compound contains halide ions (Cl-, Br- or I- )
In that case: 
Chloride produce chlorine, Cl2 
Bromides produce bromine, Br2 
Iodides produce iodine, I2

Question 14

Metal + water ->

Answer 14

Metal hydroxide + hydrogen

Question 15

Hydrogen is produced if a metal reacts with

Answer 15

Dilute acid

Question 16

Metal + acid ->

Answer 16

Salt + hydrogen

Question 17

Rates of reaction is greater in warm or cold acid?

Answer 17

WArm

Question 18

In general the more reactive the metal the greater the rate of

Answer 18

Bubbling

Question 19

Some reactive metals react unexpectedly slowly with water or acids

Answer 19

1 aluminium has a layer of aluminium oxide that stops water reaching the metal below

2 in the reaction of calcium with dilute sulfuric acid a layer of insoluble calcium surface forms slowing the reaction

3 in the reaction of magnesium with water a layer of sparingly soluble magnesium hydroxide forms slowing the reaction

Question 20

What does magnesium react vigorously with?

Answer 20

Steam

Question 21

What is the reactivity series

Answer 21

Potassium
Sodium
Calcium
Magnesium
Aluminium
Sin
Iron
—— HYDROGEN——
Copper
Silver 
Gold

Question 22

A more reactive metal will ——— a less reactive metal from its salts in solution

Answer 22

Displace

Question 23

Magnesium is more reactive than copper thederfore what happens in a copper surface solution?

Answer 23

It can displace the copper

Question 24

Magnesium displacing copper from copper sulfate solution, in this reaction you observe:

Answer 24

1 the colour of the solution fading as blue copper sulfate is replaced by colourless magnesium sulfate

2 an orange-brown coating of copper forming on the surface of the magnesium

3 an increase in temperature because reaction is exothermic

Question 25

Method for deducing a reactivity series

Answer 25

You can work out a reactivity series for metals by observing what happens when you mix different combinations of metals and their salt solutions to do this: Add a powdered metal to a test tube or beaker of a metal salt solution (as above right) or Dip a small piece of metal into a metal salt solution on a sporting tile Then look for evidence o a reaction such as a change in colour or temperature

Question 26

How are cations formed

Answer 26

Metal atoms lose electrons

Question 27

OIL RIG

Answer 27

Oxidation is loss | Reduction is gain

Question 28

Metal atoms form cations when metals react with

Answer 28

Water or dilute acids

Question 29

Metals react with water to form

Answer 29

Metal hydroxides

Question 30

Metals react with dilute acids to form

Answer 30

Salts

Question 31

Displacement reactions are known as

Answer 31

Redox reactions

Question 32

Shat happens in redox atoms

Answer 32

The atoms of the more reactive metal are oxidised - they lose electrons The metal cations of the less reactive metals are reduced - they gain electrons

Question 33

Most metals are extracted by the

Answer 33

Reduction of ores found in the earths crust

Question 34

What’s an ore

Answer 34

Is a rock that contains enough of a metal to make its extraction economical

Question 35

Rocks may contain too little metal to make extraction worthwhile so over time metal prices may

Answer 35

Rude and these low-grade ores may become useful

Question 36

Unreactive metals

Answer 36

Such as gold are placed at the bottom of reactivity series Found in earths crust In their ‘native state’ unconvinced with other elements: They are not found as compounds but They may occur naturally as alloys (mixtures of metals)

Question 37

Oxidation is

Answer 37

The gain of oxygen by a substance eg magnesium is oxidised to magnesium oxide in air 2Mg + O2 -> 2MgO The loss of electrons by a substance eg Mg -> Mg2+ + 2e-

Question 38

Reduction is

Answer 38

The loss of oxygen by a substance eg zinc oxide is reduced to zinc when it is heated with carbon : ZnO + C -> Zn + CO the gain of electrons by a substance eg Zn2+ + 2e- -> Zn

Question 39

Resistance to corrosion

Answer 39

Metals corrode when they react with substances around them such as air and water. How easily a metal corrodes depends on how reactive it is

Question 40

What metal does not corrod

Answer 40

Gold

Question 41

Easily corrodes is at the ——— of the reactivity series

Answer 41

Top

Question 42

The method used to extract a metal from its ore is related to

Answer 42

Cost of extraction process Posting in reactivity series In principle, all metals can be extracted from their compounds using electrolysis. But: Electricity is needed, which is expensive Reduction by heating with carbon can be used if a metal is less reactive than carbon Chemical reactions may be needed to separate silver and gold from other metals

Question 43

Iron extraction

Answer 43

Iron is less reactive than carbon So it’s produced by reducing iron oxide using carbon This happens in industrial equipment called a blast furnace

Question 44

Iron extraction At the high temperatures inside the blast furnace :

Answer 44

Iron oxide is reduced by carbon Iron oxide + carbon -> iron + carbon monoxide Also it’s reduced by carbon monoxide Iron oxide + carbon monoxide -> iron + carbon dioxide Molten iron is produced

Question 45

Aluminium extraction

Answer 45

Aluminium is more reactive than carbon it is produced by reducing aluminium oxide in and electrolytic cell

Question 46

Aluminium extraction steps

Answer 46

1 aluminium oxide is dissolved in molten cryolite. This reduces the temperature needed for electrolysis to happen when an electric current passes through the mixture 1 at the cathode aluminium ions gain electrons and are reduced to aluminium atoms: Al3+ + 3e- -> Al 3 at anode oxide ions lose electrons and form oxygen gas: 2O2- -> O2 + 4e- Oxygen reacts with the graphite anodes so these must be replaced every few weeks