C4 CHEMICAL REACTIONS

Question 1

oxidation/reduction?

Answer 1

oxidation = gains oxygen
reduction = loses oxygen

Question 2

what is the reactivity series of metals? what are the trends in reactivity metals in order with acids/water

Answer 2

the series shows the metal in order of their reactivity

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

metals below H2 in the series don’t react with acids.

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

Question 3

displacement reaction?

Answer 3

when a more reactive metal 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 be 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

by electrolysis

Question 7

oxidation and reduction in terms of electrons?

Answer 7

oxidation - loss of electron
reduction - gain of electron

Oxidation
Is
Loss
Reduction
Is
Gain

Question 8

equation for metal and acid?

Answer 8

metal + acid –> salt + hydrogen

Question 9

equation for metal oxide and acid

Answer 9

metal oxide + acid –> salt + water

Question 10

equation for metal oxide and acid

Answer 10

metal oxide + acid –> salt + water

Question 11

equation for metal hydroxide and acid

Answer 11

metal hydroxide + acid –> salt + water

Question 12

equation for metal hydroxide and acid

Answer 12

metal hydroxide + acid –> salt + water

Question 13

equation for metal carbonate and acid

Answer 13

metal carbonate + acid –> salt + water + carbon dioxide

Question 14

equation for metal carbonate and acid

Answer 14

metal carbonate + acid –> salt + water + carbon dioxide

Question 15

which metals in the reactivity series will react with acid?

Answer 15

those above hydrogen

Question 16

general equation for neutralisation

Answer 16

base + acid –> salt + water

Question 17

redox equation?

Answer 17

both oxidation and reduction occurs

Question 18

base?

Answer 18

any substance that reacts with an acid to form a salt and water only.
compounds that neutralise acids

Question 19

explain in terms of gain or loss of electrons which species have been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid

Answer 19

magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)
hydrogen in HCl has gained electrons and thus have been reduced (H+ to H2)

Question 20

explain in terms of gain or loss of electrons which species have been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid

Answer 20

magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)
hydrogen in HCl has gained electrons and thus have been reduced (H+ to H2)

Question 21

how is a soluble salt formed?

Answer 21

react to the excess acid with some insoluble chemical (e.g metal oxide)
filter off the leftovers
crystallise the product

Question 22

what do acids and alkalis produce in aqueous solution?

Answer 22

acid produces hydrogen ions
alkalis produce hydroxide ions

Question 23

what are acids?

Answer 23

produce hydrogen ions in aqueous solution

Question 24

what are alkalis?

Answer 24

soluble bases produce hydroxide ions in aqueous solution

Question 25

what is the pH scale?

Answer 25

the measure of acidity

Question 26

what does pH level of 7?

Answer 26

neutral solution

Question 27

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

Answer 27

H+ + OH- ---> H20

Question 28

strong acid?

Answer 28

completely ionised in aqueous solution

Question 29

weak acid?

Answer 29

partially ionised in aqueous solution

Question 30

what happens to PH level as concentration of H+ increases?

Answer 30

ph decreases

Question 31

what is concentrated acid? and what is a diluted solution? is this the same as a strong and weak acid?

Answer 31

- has more moles of acid per unit volume than dilute (dilute refers to solutions of low concentrations) - it is not the same - concentration is not the strength of an acid. - strength refers to whether the acid is completely ionised in water (strong) or only partially ( weak)

Question 32

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

Answer 32

increases by a factor of 10

Question 33

name the following salts? LiNO3 , K2CO3 , MgBr2 , BaSo4

Answer 33

lithium nitrate , potassium carbonate , magnesium bromide , barium sulfate

Question 34

electrolysis?

Answer 34

decomposition of an electrolyte by an electric current.

Question 35

electrolyte?

Answer 35

liquid/solution which conducts electricity

Question 36

cathode?

Answer 36

negative electrode

Question 37

anode?

Answer 37

positive electrode

Question 38

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

Answer 38

reduction = cathode oxidation = anode

Question 39

in aqueous electrolysis , which element is discharged at the cathode ? oxygen is produced at the anode unless what?

Answer 39

less reactive element discharges at the cathode. hydrogen is produced unless there is a less reactive metal , in which case the said metal is produced . oxygen is produced at the anode unless the solution contains halide ions in which case halogen molecules are produced

Question 40

how is aluminium manafactured?

Answer 40

made through electrolysis of aluminium oxide and cryoilte. lots of energy is needed to produce the current in electrolysis which makes this process expensive

Question 41

half equation for the extraction of aluminium?

Answer 41

al3+ + 3e- --> Al ( cathode) 2 O2- --> O2 + 4e- (anode) oxygen needs to react with C of the anode producing CO2

Question 42

why is cryolite used in manufacturing of aluminium?

Answer 42

lowers melting point = reduces energy costs

Question 43

half equation in electrolysis of the aqueous Na2SO4?

Answer 43

2H+ + 2e- --> H2 (cathode) 4OH- --> 2H2O + O2 + 4e- (anode)

Question 44

half equation in electrolysis of the molten and aqueous KCl?

Answer 44

K+ + e- --> K (cathode) 2Cl- ---> Cl2 + 2e- (anode) 2H+ + 2e- --> H2 (cathode) 2Cl- ---> Cl2 + 2e- (anode) respectively

Question 45

half equations in electrolysis of the aqueous CuBr2?

Answer 45

Cu2+ + 2e- --> Cu (cathode) 2Br- ---> Br2 + 2e- (anode)

Question 46

REQUIRED PRACTICAL: how could you prepare a sample of pure , dry copper sulfate crystals from a sample of insoluble copper sulfate?

Answer 46

react sulfuric acid with excess copper oxide. filter to remove the excess copper oxide heat the solution to evaporate turn off the heat and leave until all the water has evaporated left with copper sulfate crystals.

Question 47

REQUIRED PRACTICAL: chemical equation for the reaction between CuO and H2SO4

Answer 47

CuO + H2SO4 ---> CuSO4 + H2O

Question 48

REQUIRED PRACTICAL: safety precautions need to be considered when preparing a pure dry salt from insoluble compound

Answer 48

bunsen burner should not be turned off or put on the safety flame when not in use. sulfuric acid corrosive so eye wear protection

Question 49

REQUIRED PRACTICAL: separate an insoluble product from a solution?

Answer 49

filtration: filter paper placed in a funnel over a conical flask pour mixture through the funnel. insoluble product left on the filter paper

Question 50

REQUIRED PRACTICAL: separate soluble from solutions?

Answer 50

place the mixture in an evaporating dish slowly heat the solution the solvent evaporates and the solution becomes more concentrated so crystals will start to form. keep heating the evaporating dish until you have dry crystals

Question 51

REQUIRED PRACTICAL: separate solid from a solution of the solid decomposes when heated?

Answer 51

crystallisation: pour the solution into an evaporating dish and heat gently. when the crystals form , remove the dish from the heat and leave to cool. once cold, filter the crystals out of the solution and leave them in a warm place to dry.