Unit 9.4+ [Reactivity Series, Electrolysis] Flashcards
Reacts vigorously with water
Most?
K, Na, Ca
Most K
Then Na
Then Ca
[REFER to paper!]
Describe the reaction:
GENERAL, GO FURTHER DOWN IN CARDS FOR TEACHER NOTES.
potassium, sodium and calcium with cold water - provides metal hydroxide + H2
- K (violently)
Potassium: Reacts violently with cold water, producing potassium hydroxide and hydrogen gas. The reaction is exothermic, often igniting the hydrogen.
w/ acid, reacts explosively
- Na (violently)
Sodium: Exhibits a less intense reaction than potassium but still produces sodium hydroxide and hydrogen gas. The reaction is also exothermic but less violent.
- Ca (less violently)
Calcium: Shows a more moderate reaction with water, forming calcium hydroxide and hydrogen gas. The reaction is less vigorous compared to potassium and sodium.
+ also w/ hot water
Describe the reaction: magnesium with steam -
producing metal oxide + H2
e.g. Al, Fe as well
Unlike alkali metals, Mg does not react noticeably with cold water.
When exposed to steam, it reacts to form magnesium oxide and hydrogen gas. This reaction is less vigorous and indicates magnesium’s lower reactivity compared to alkali metals.
Magnesium reacts with steam to form magnesium oxide and hydrogen.
Mg (s) + H2O (g) -> MgO + H2
no reaction w/ water whether hot (l), cold (l) or steam (g)
lead, copper, silver, gold
describe reaction: magnesium, zinc, iron, copper, silver and gold
with dilute hydrochloric acid
- Mg
Mg → Reacts rapidly/vigorously with dilute hydrochloric acid, producing magnesium chloride and hydrogen gas. Reaction is vigorous.
- Zinc
Zn → Also reacts with dilute hydrochloric acid but at a slower rate than magnesium, producing zinc chloride and hydrogen gas.
reacts slowly
- Iron
Fe → Shows a slower reaction compared to zinc, forming iron(II) chloride and hydrogen gas.
- Copper
Cu → Barely reacts with dilute hydrochloric acid, indicating its low reactivity.
- Silver & Gold
Ag & Au → Do not react with dilute hydrochloric acid. Their position in the reactivity series explains their lack of reactivity.
Why does this trend exist?
Ag & Au cannot displace hydrogen from HCl. Silver is below hydrogen in the reactivity series and thus cannot displace it.
Metals that react vigorously, producing a lot of heat and gas quickly, like potassium and sodium, are considered…
highly reactive
Metals that react slowly or not at all, like silver and gold, are considered…
less reactive
Describe relative reactivities of metals w/ tendency to form positive ions, by
displacement reactions, if any, with the aqueous
ions of Mg, Zn, Fe, Cu, & Ag
Bc
How easily do highly reactive metals lose electrons?
Reactivity is closely linked to a metal’s tendency to form positive ions:
Highly reactive metals like potassium and sodium lose electrons easily, forming positive ions rapidly.
How easily do less reactive metals lose electrons?
Less reactive metals like silver and gold have a lower tendency to lose electrons and form positive ions.
Aluminium, though high in the reactivity series, often appears less reactive
Why?
due to the formation of a protective oxide layer on its surface, which prevents further reaction with air or water.
Once this layer is removed or disrupted, aluminium’s true reactivity is observed.
Why is potassium more reactive?
Though K and Na both have 1 valence electron,
K’s valence electron is further from the nucleus so it is easier to lose that electron to become a cation.
Why is potassium more reactive than calcium specifically?
Consider electronic configuration
Both have four electron shells
BUT the more protons in the nucleus, the harder it is to lose a valence electron to become a cation
+ 1 valence electron is easier to lose than 2
Metal, Reaction with water
- Calcium
Bubbles of gas are given off after a few seconds.
When tested with universal indicator the water is now alkaline
- Sodium
The sodium melts and skims over the surface producing a stream of small bubbles.
Sometimes a yellow-orange flame appears
Potassium
It immediately produces a lilac flame as it skims around the surface making a fizzing noise
What does this stand for:
Please send Charlie’s monkeys and carbon zebras in tall lead hellish cages securely guarded.
POTASSIUM
SODIUM
CALCIUM
MAGNESIUM
ALUMINIUM
Carbon
ZINC
IRON
Tin
LEAD
Hydrogen
COPPER
SILVER
GOLD
Practical Implications
Predicting Reactions: It helps in predicting the outcome of reactions involving different metals.
Extraction of Metals: The method of metal extraction from its ore is often determined by its position in the series.
Corrosion and Protection: Understanding reactivity helps in developing methods to protect metals from corrosion.
In a displacement reaction…
the metal in a compound is replaced by the more reactive metal to form a new compound
Mg + CuSO4 =>
Cu + MgSO4
bc Mg more reactive so Cu replaced
Define electrolysis
the decomposition of an
ionic compound, when molten or in aqueous solution, by the passage of an electric current
anode
positive electrode
cathode
negative electrode
electrolyte
the molten or aqueous
substance that undergoes electrolysis
Describe the transfer of charge during electrolysis to include:
(a) the movement of electrons in the external circuit
(b) the loss or gain of electrons at the electrodes
(c) the movement of ions in the electrolyte
a)
b)
c)
State where metals/hydrogen are formed?
Where are non-metals (except hydrogen) formed?
metals or hydrogen are formed at the cathode and that non-metals (other than
hydrogen) are formed at the anode
Why are metal objects electroplated?
metal objects are electroplated to improve their appearance and resistance to
corrosion
How does a hydrogen-oxygen fuel cell work?
hydrogen–oxygen fuel cell uses
hydrogen and oxygen to produce electricity with
water as the only chemical product
Extraction of Metals
What are ores?
Some unreactive metals can be found as elements. Native metals.
Most metals found naturally in rocks - called ores. In compounds, chemically bonded to other elements.
Metals below carbon are…
Extracted by REDUCTION
using carbon, coke, or charcoal
cheap process as carbon is cheap & can be source of heat
Unreactive metals do not…
They do not need to be extracted - found as pure element (native)
occurs as they do not easily react with other substances due to their chemical stability
Metals above carbon
Why?
Extracted by electrolysis
Bc the REACTIVITY of a metal determines the METHOD of extraction
large amount of electricity required so expensive
Aluminium extraction using?
What is bauxite?
Properties
Electricity, by electrolysis of molten bauxite
Most common aluminium ore Al2O3
Bauxite - high melting point 2000 Celsius.
Why is aluminium oxide dissolved in molten cryolite?
REMEMBER the word “cryolite”
reduce the overall melting point of the mixture, making it easier to melt and reducing electricity required for electrolysis process
cryolite used as: -lowers operating temperature
-increases conductivity
Overall
4Al2O3 (l) -> 4Al (l) + 3O2 (g)
Ionic main equation
2Al2O3 -> 4Al3+ + 6O2-
Half equations
At the NEGATIVE cathode
Al3+ + 3e- -> Al
At the positive anode
2O2- -> O2 + 4e-
On diagram, there is
Graphite anode [in middle, positive)
Graphite cathode [bracketing anode, negative]
Molten aluminium coming out right
Purified aluminium ore dissolved in molten cryolite
+ Steel case
The Process of Aluminium Extraction by Electrolysis
1.
Bauxite is first purified to produce aluminium oxide, Al2O3
2.
Aluminium oxide is then dissolved in molten cryolite
This is because aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive
The resulting mixture has a lower melting point without interfering with the reaction
3.
The mixture is placed in an electrolysis cell, made from steel, lined with graphite
- What does graphite lining do?
The graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrodes
At the cathode (negative electrode):
REDUCTION = GAIN E-
FORM AL
Aluminium ions gain electrons (reduction)
Molten aluminium forms at the bottom of the cell
The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell
Al3+ + 3e- → Al
At the anode (positive electrode):
Oxide ions lose electrons (oxidation)
Oxygen is produced at the anode:
2O2- → O2 + 4e-
The overall equation for the reaction is:
2Al2O3 → 4Al + 3O2
The carbon in the graphite anodes reacts with the oxygen produced to produce CO2
C (s) + O2 (g) → CO2 (g)
As a result the anode wears away and has to be replaced regularly
A lot of electricity is required for this process of extraction, this is a major expense
Why aluminium used for foil & food cans
Doesn’t corrode easily bc has a strong oxide coating on its surface, which protects the aluminium from further reaction
Why in aerospace industry?
Has low density, light
Extraction of Iron from Hematite
Where? From its…?
This produces how many tonnes of iron/day?
Iron is extracted in a large container called a blast furnace from its ore, hematite
Modern blast furnaces produce approximately 10,000 tonnes of iron per day
Raw materials
added where?
iron ore (hematite)
coke (an impure form of carbon)
& limestone
are added into the top of the blast furnace
What is blown into the bottom?
Hot air
Zone 1
Carbon-rich coke burns in the hot air blasted in to the furnace, reacting with oxygen in air, to produce carbon dioxide.
The reaction = exothermic so it gives off heat, heating the furnace. Produces lots of heat energy
C (s) + O2 (g) -> CO2 (g)
carbon + oxygen → carbon dioxide
Zone 2
The carbon dioxide reacts with more hot coke to form carbon monoxide [at high temp in furnace]
Carbon dioxide has been reduced to carbon monoxide
CO2 (g) + C (s) -> 2CO (g)
carbon + carbon dioxide → carbon monoxide
Zone 3
The carbon monoxide then reacts w/ the iron oxide from the haematite to produce CO2 and Fe; it reduces the iron oxide [in the iron ore] to form iron
This will melt and collect at the bottom of the furnace, where it is tapped off:
Fe2O3 (s) + 3CO (g) -> 2Fe (l) + 3CO2 (g)
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Why is limestone, CaCO3, added?
added to the furnace to remove impurities in the ore.
Limestone thermally decomposes to form CaO and the product further reacts with the impurities to form slag, CaSiO3.
The calcium oxide formed reacts with the silicon dioxide, which is an impurity in the iron ore, to form calcium silicate
What happens to it then?
Equations?
CaCO3 (s) -> CaO (s) + CO2 (g)
calcium carbonate → calcium oxide + carbon dioxide
CaO (s) + SiO2 (s) -> CaSiO3 (s)
calcium oxide + silicon dioxide → calcium silicate
melts and collects as a molten slag floating on top of the molten iron, which is tapped off separately
Actual equation cards - test self: symbol equations for the different stages of the extraction of iron from hematite are:
- Zone 1: The burning of carbon (coke) to provide heat and produce carbon dioxide:
C (s) + O2 (g) → CO2 (g)
Zone 2: The reduction of carbon dioxide to carbon monoxide:
CO2 (g) + C (s) → 2CO (g)
Zone 3: The reduction of iron(III) oxide by carbon monoxide:
Fe2O3 (s) + 3CO (g) → 2Fe (I) + 3CO2 (g)
The thermal decomposition of calcium carbonate (limestone) to produce calcium oxide:
CaCO3 (s) → CaO (s) + CO2 (g)
The formation of slag:
CaO (s) + SiO2 (s) → CaSiO3 (l)
Acid-base reaction
Name the three products formed when tin(II) nitrate is heated.
oxidised, NO2, O2
tin oxide, nitrogen dioxide, oxygen
Steel articles can be plated with tin or zinc to prevent rusting.
When the zinc layer is damaged exposing the underlying steel, it does not rust, but when
the tin layer is broken the steel rusts.
Explain. [4]
zinc is more reactive than iron [1]
tin is less reactive than iron [1]
zinc provides sacrificial protection [1]
Iron corrodes/reacts [1]
Explain why it is necessary to use a mixture, alumina and cryolite, rather than just
alumina.
lowers melting point [1]
reduces amount of energy needed / reduces cost
Explain, in terms of electron transfer, why the more reactive metal is always the negative
electrode.
metals react by losing electrons (1)
the more reactive metal/ zinc will lose electrons more readily (making the
electrode negatively charged). (1)
dissolving → filtration → evaporation → crystallisation
🔗
Four steps to prepare a salt from an excess of a solid base and an acid:
neutralisation -> evaporation -> filtration -> crystallisation
//
2, 1, 2, 3
filter, concentrate resulting solution, filter, heat crystals
Salts can be made by adding different substances to dilute hydrochloric acid.
For which substance could any excess not be removed by filtration?
C) sodium hydroxide
The substance for which any excess cannot be removed by filtration is sodium hydroxide (C). When sodium hydroxide is added to dilute hydrochloric acid, a neutralization reaction occurs, resulting in the formation of water and a salt called sodium chloride.
Which method is used to make the salt copper sulfate?
dilute acid + carbonate
Which of the following methods are suitable for preparing both zinc sulfate and copper sulfate?
1
2
3
Reacting the metal oxide with warm dilute aqueous sulfuric acid.
Reacting the metal with dilute aqueous sulfuric acid.
Reacting the metal carbonate with dilute aqueous sulfuric acid.
B) 1 and 3 only
A compound is a salt if it
is formed when an acid reacts with a base.
Salts can be prepared by reacting a dilute acid
1 with a metal;
2 with a base;
3 with a carbonate.
Which methods could be used to prepare copper(II) chloride?
2 & 3 only
Which methods of salt preparation are suitable for copper(II) chloride?
1 Add copper(II) carbonate to dilute hydrochloric acid.
2 Add copper to dilute hydrochloric acid.
3 Warm copper(II) oxide with dilute hydrochloric acid.
1 & 3
Copper does not react with acid because in the reactivity series copper is placed below the hydrogen.
The reaction between copper(II) carbonate and dilute hydrochloric acid is shown below.
CuCO3+2HCl⟶CuCl2 + H2O+CO2
The reaction between copper (II) oxide and dilute hydrochloric acid is shown below.
CuO+2HCl→CuCl2 +H2O
BELOW HYDROGEN means
DOES NOT REACT W/ ACID
Describe the stages in the preparation of a sample of DRY copper sulfate crystals using SULFURIC ACID and COPPER(II) OXIDE and the following equipment. Include a balanced equation. (7 marks)
React EXCESS copper oxide with sulfuric acid
Stir and heat mixture in a conical flask
Filter off excess black solid (copper oxide)
Concentrate solution by heating in an evaporating basin
Leave to stand and cool slowly to form crystals
Dry crystals between filter papers/in oven
CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O (l)
