T4 chemical changes

Question 1

what is oxidation/reduction

Answer 1

oxidation - when a substance gains oxygen

reduction - when a substance loses oxygen

Question 2

what are the trends in reactivities of metals in reactions with acids/water

Answer 2

metals above H2 in reactivity react with acid to produce H2, the more reactive the metal is, the quicker and more violent reaction with acid occurs

metals below H2 don’t react with acid

not all metals above H2 react with water - mostly group 1 and 2 metals
aluminium is the borderline case

Question 3

what is a displacement reaction

Answer 3

reaction where a more reactive metals displaces a less reactive metal from a compound

Question 4

how are unreactive metals found in earth

Answer 4

in their natural state

Question 5

how can metals less reactive than carbon be extracted

Answer 5

reduction with carbon

carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides

metal from the metal oxide gets reduced to the pure metal

Question 6

how are metals more reactive than carbon extracted

Answer 6

electrolysis

Question 7

how are oxidation and reduction defined in terms of electron transfer

Answer 7

oxidation - loss of electrons

reduction - gain of electrons

Question 8

general equation for a reaction between metals and acids

what type of reaction is this

Answer 8

metal + acid > salt + hydrogen

redox reaction, also displacement reaction

Question 9

which metals in the reactivity series will react with acid

Answer 9

those above hydrogen

Question 10

general equation for a neutralisation reaction

Answer 10

base + acid > salt + water

Question 11

general equation for the reaction between metal carbonate and acid

Answer 11

metal carbonate + acid > salt + water + carbon dioxide

Question 12

general equation for the reaction between metal oxides and acids

Answer 12

metal oxide + acid > a salt + water

Question 13

what is a redox reaction

Answer 13

reaction where both oxidation and reduction occurs

Question 14

how is a soluble salt formed

Answer 14

1. react the excess with some insoluble chemicals
2. filter off the leftovers
3. crystalise the product

Question 15

what do acids and alkalis produce in aqueous solutions

Answer 15

acids - hydrogen ions

alkalis - hydroxide ions

Question 16

what are bases, acids and alkalis

Answer 16

b - compounds that neutralise acids
acids - produce hydrogen ions in aqueous solutions
alkalis - soluble bases which produce hydroxide ions in aqueous solutions

Question 17

what is the pH scale and what does a pH of 7 show

Answer 17

measure of acidity/alkalinity of a solution

neutral solution

Question 18

state the general equation for a neutralisation reaction in a short, ionic form

Answer 18

H+ + OH- > H2O

Question 19

what is a strong acid and a weak acid

Answer 19

S - completely ionised in aqueous solution

w - only partially ionised in aqueous solution

Question 20

what happens to pH as concentration of H+ increases

Answer 20

decreases

Question 21

what is a concentrated acid and what is a dilute acid

is this the same as a strong and weak acid

Answer 21

c - has more moles of acid per unit volume than dilute
d - refers to solutions of low concentration

not the same - concentration is different to strength of an acid

strength refers to whether the acid is completely ionised in water (strong) or only partially (weak)

Question 22

as the pH is decreased by one unit, what change is seen in the hydrogen ion concentration

Answer 22

increases by a factor of 10

Question 23

what is electrolysis

Answer 23

passing of an electric current through ionic substances that are molten or in solution to break them down into elements

ions are discharged at electrodes to produce these

Question 24

what is an electrolyte

Answer 24

liquid/solution which conducts electricity

Question 25

what is a cathode and what is an anode

Answer 25

c - negative electrode

a - positive electrode

Question 26

what occurs at the cathode and what occurs at the anode during electrolysis

Answer 26

c - reduction occurs

a - oxidation occurs

Question 27

in aqueous electrolysis, which element is discharged at the cathode

oxygen is produced at the anode unless what

Answer 27

less reactive element discharges at the cathode, hydrogen is produced unless there is a less reactive metal in which the metal is produced

oxygen is produced at anode unless the solution contains halide ions in which halogen molecules are produced

Question 28

how is aluminium manufactured

why is it expensive

Answer 28

made through the electrolysis of aluminium oxide and cryolite

lots of energy is needed to produce the current in electrolysis which makes this process expensive

Question 29

half equations in the extraction of aluminium

Answer 29

Al3+ + 3e- > Al (cathode)
2O2- >O2 + 4e- (anode)

oxygen reacts with C of the anode producing CO2

Question 30

why is cryolite used in manufacturing of aluminium

Answer 30

lowers the melting point of aluminium oxide, reducing energy costs

Question 31

what are the half equations in electrolysis of the aqueous Na2SO4

Answer 31

2H+ + 2e- > H2 (cathode)

4OH- > 2H2O + O2 + 4e- (anode)

Question 32

what are the half equations in electrolysis of the molten and aqueous KCl

Answer 32

K+ + e- > K (cathode)
2Cl- > Cl2 + 2e- (anode)

2H+ + 2e- > H2 (cathode)
2O2- > O2 + 4e- (anode)

Question 33

half equations in electrolysis of the aqueous CuBr2

Answer 33

Cu2+ + 2e- > Cu (cathode)

2Br- > Br2 + 2e- (anode)