C6-Electrolysis Flashcards
(86 cards)
1
Q
What is an anode?
A
the positive electrode in electrolysis
2
Q
What is brine?
A
concentrated sodium chloride solution that can undergo electrolysis to produce chlorine gas, hydrogen gas, and sodium hydroxide solution
3
Q
What is a cathode?
A
the negative electrode in electrolysis
4
Q
What is an electrolyte?
A
a liquid, containing free-moving ions, which is broken down by electricity in the process of electrolysis
5
Q
What is a half equation?
A
an equation that describes reduction or oxidation
6
Q
What does inert mean?
A
unreactive
7
Q
What are cations?
A
positive ions
8
Q
What are anions?
A
negative ions
9
Q
Where do cations move towards during electrolysis?
A
the cathode
10
Q
Where do anions move towards during electrolysis?
A
the anode
11
Q
What are the electrodes made out of?
A
carbon graphite because it is a conductor, but also unreactive and has a high melting point
12
Q
What happens to the ions at the electrodes?
A
they are discharged and they form elements
13
Q
What is electrolysis?
A
The decomposition of an ionic compound by electricity
14
Q
Why can’t covalent substances be broken down by electrolysis?
A
For a substance to be broken down by electrolysis, it must contain ions as they have a charge. Covalent substances do not contain charged ions, only neutral atoms
15
Q
What type of reaction happens at the anode and why?
A
Oxidation, this is because the negative ions lose electrons to the positive anode
16
Q
What type of reaction happens at the cathode and why?
A
Reduction, Positive ions gain electrons from the negative cathode
17
Q
Describe the movement of electrons during electrolysis
A
Electrons move from the positive anode towards the negative electrode through the circuit
18
Q
What is the -ve electrode?
A
Cathode (negative)
19
Q
What is the +ve electrode?
A
Anode (Positive)
20
Q
Describe what would happen at the -ve electrode in the electrolysis of PbBr₂(l)
A
Grey/black deposit
Pb²⁺ ions attracted
Half equation: Pb²⁺ + 2e⁻ -> Pb
Gains electrons therefore reduction
21
Q
Describe what would happen at the +ve electrode in the electrolysis of PbBr₂(l)
A
Bubbles of red-brown vapour
Br⁻ ions attracted
half equation: 2Br⁻ -> Br₂ + 2e⁻
Loses electron therefore oxidation
22
Q
Describe what would happen at the -ve electrode in the electrolysis of NaCl(l)
A
Grey/black deposit
Na⁺ ions attracted
half equation: Na⁺ + e⁻ -> Na
Gain of electrons therefore reduction
23
Q
Describe what would happen at the +ve electrode in the electrolysis of NaCl(l)
A
bubbles of green vapour
Cl⁻ ions attracted
half equation: 2Cl⁻ -> Cl₂ + 2e⁻
Loses electrons, therefore oxidation
24
Q
Describe what would happen at the -ve electrode in the electrolysis of Al₂O₃(l)
A
grey/black deposit
Al³⁺ ions attracted
half equation: Al³⁺ + 3e⁻ -> Al
Gains electrons, therefore reduction
25
Describe what would happen at the +ve electrode in the electrolysis of Al₂O₃(l)
Bubbles of colourless vapour
O²⁻ ions attracted
half equation: 2O²⁻ -> O₂ + 4e⁻
Loses electrons, therefore oxidation
26
Why does electrolysis only work when the ionic substance is molten or dissolved?
The ions are only free to move once molten or as an aqueous solution, as a solid they are fixed in a structure and cannot move
27
Which negative ions are attracted towards the positive electrode and why?
anions (negative ions) are attracted towards the positive electrode because they are oppositely charged
28
What is the product at the cathode during the electrolysis of an aqueous solution?
At the negative electrode,The less reactive element forms and discharges at the cathode.Hydrogen is produced unless there is a less reactive metal,in which the metal is produced
29
What is the product at the anode during the electrolysis of and aqueous solution?
At the positive electrode, oxygen is produced unless the solution contains halide ions
30
What metals are less reactive than hydrogen?
What metals are less reactive than hydrogen?
31
What is the equation for the product at the cathode in the electrolysis of aqueous solutions
Metal less reactive than hydrogen: Xʸ⁺ + ye⁻ -> X
| No metal less reactive than hydrogen: 2H⁺ +2e⁻ -> H₂
32
What happens during the process of electrolysis?
An electric current passes through the electrolyte, causing positively charged ions to move to the cathode (negative electrode) and negatively charged ions to move to the anode (positive electrode).
33
What does it mean when "a safer alternative for practical work is anhydrous zinc chloride"?
It means that anhydrous zinc chloride, which does not contain water, is less hazardous to use during electrolysis experiments compared to other molten ionic compounds, making it safer for students in practical settings.
34
Why is electrolysis used instead of reduction with carbon or if the metal reacts with carbon?
Electrolysis is used if the metal is too reactive to be extracted by
reduction with carbon or if the metal reacts with carbon
35
What is cryolite
Cryolite is a mineral that reduces the melting point of aluminum oxide during electrolysis.
36
why is cryolite used in the electrolysis of aluminum oxide?
This lowers the energy required for the process, making it more efficient and cost-effective.
37
Why must the positive electrode have to be replaced at regular intervals
The anode needs to be replaced regularly in aluminium extraction because the carbon in the graphite anodes reacts with the oxygen produced to form COz, causing the anode to wear away.
38
Why is aluminium expensive?
High cost of electricity to perform electrolysis and also high cost of continuously replacing electrodes
39
Required practical:Electrolysis
Set up the electrolysis apparatus with two inert electrodes (e.g., graphite or platinum).
Connect the electrodes to a power source.
Add the aqueous solution (e.g., sodium chloride, copper sulfate).
Observe and record the products at the cathode and anode (e.g., bubbles, color changes, smell).
Use appropriate tests to identify the gases produced:
Hydrogen gas: Makes a squeaky pop when tested with a lit splint.
Oxygen gas: Relights a glowing splint.
Chlorine gas: Turns damp blue litmus paper red, then bleaches it white.
40
Independent variable for required practical of electrolysis
The type of aqueous solution used (e.g., sodium chloride, copper sulfate, etc.).
41
Dependent variable for required practical of electrolysis
The products formed at the cathode and anode (e.g., gases, metals, or other observations).
42
Control variable for required practical of electrolysis
Volume of the solution (keep it constant to ensure fair testing).
Concentration of the solution (to maintain consistent ion availability).
Current or voltage applied (to avoid affecting the rate or products of electrolysis).
Type of electrodes (use inert electrodes like graphite or platinum for consistency).
Duration of electrolysis (allow the same time for each test).
43
Equipment for electrolysis required practical
Power supply
To provide the electric current needed for electrolysis.
Inert electrodes (e.g., graphite or platinum)
These do not react with the electrolyte or products.
Electrolysis cell or a beaker
To hold the aqueous solution being tested.
Wires and crocodile clips
To connect the electrodes to the power supply.
Aqueous solutions
Examples: sodium chloride (NaCl), copper sulfate (CuSO₄), or dilute sulfuric acid (H₂SO₄).
Test tubes
To collect and test any gases produced.
Splints (wooden splints)
For gas tests (e.g., glowing splint for oxygen, lit splint for hydrogen).
Litmus paper
To test for chlorine gas (blue litmus turns red, then white).
Measuring cylinder
To measure the volume of the aqueous solution.
Clamp stand and holder
To hold the electrodes in place securely.
44
What must be used to perform electrolysis?
Large
amounts of energy are used in the extraction process to melt the
compounds and to produce the electrical current.
45
Why is a mixture used as the electrolyte in some electrolysis processes (e.g., aluminum extraction)?
Lower Melting Point:
A mixture, such as aluminum oxide with cryolite, is used to lower the melting point of the electrolyte.
This reduces the energy required for the process, making it more cost-effective.
Improved Conductivity:
The mixture enhances the electrical conductivity of the electrolyte, allowing the current to flow more efficiently.
Facilitates Ion Movement:
The addition of substances like cryolite allows the molten electrolyte to remain in a liquid state at a lower temperature, enabling the free movement of ions required for electrolysis.
46
When do you usually need a mixture for electrolysis
If the melting point is too high, like with aluminium oxide, you need a mixture (e.g. with cryolite) to reduce the temperature required and save energy.
47
When can you perform electrolysis without it being a mixture?
If the pure substance melts at a reasonably low temperature
Some ionic compounds (like lead bromide) have lower melting points and can be used in pure molten form.
🔥 Example: Molten lead bromide (PbBr₂) is often used in electrolysis without mixing.
If the substance is dissolved in water
Electrolysis can be done with aqueous solutions (e.g. salt water, copper sulfate solution).
In this case, the substance is not molten, but dissolved — so it's still technically not a mixture for melting point purposes.
48
Why do hydrogen and hydroxide ions get discharged during electrolysis of aqueous solutions?
This happens because in the aqueous solution water molecules
break down producing hydrogen ions and hydroxide ions that are
discharged.
49
How can you predict the products of the electrolysis of aqueous solutions containing a single ionic compound?
At the Cathode (-):
If the metal is more reactive than hydrogen (e.g. sodium, potassium, calcium), hydrogen gas is produced from the reduction of H⁺ ions.
If the metal is less reactive than hydrogen (e.g. copper, silver), the metal is deposited.
At the Anode (+):
If the solution contains halide ions (Cl⁻, Br⁻, I⁻), the halogen is produced.
If no halide ions are present, oxygen gas is produced from the oxidation of OH⁻ ions.
50
Reduction
Gain electrons but lose oxygen
51
Oxidation
Lose electrons but gain oxygen
52
What is thr equation which stays the same if oxygen is given off at the anode
4OH- – 4e- → O2 + 2H2O
53
What is the equation if hydrogen is given off st the cathode?
2H+ + 2e- → H2
54
OILRIG
Oxidation is loss,Reduction is gain
55
Can metals that react with carbon be extracted by electrolysis as well?
Yes
56
What occurrs at the cathode during electrolysis
Reduction
57
What occurs at the anode during electrolysis
Oxidation
58
How is aluminium manufactured?
Aluminium is made through the electrolysis of aluminium oxide and cryolite.
59
What are the half equations in electrolysis of the aqueous Na2 SO4?
2 H* + 2 e → H2 (cathode)
40H- → 2H20 + 02 + 4 e (anode)
60
What are the half equations in electrolysis of the molten and aqueous KCI?
K+ + e → K (cathode)
2 Cl → Cl, 2+ 2 e (anode)
2H* + 2 e → H2 (cathode)
2 Cl → Cl, + 2 e (anode), respectively
61
What would you observe at each electrode when copper chloride solution is electrolysed?
Positive electrode: Bubbles of gas (chlorine)
Negative electrode: Electrode coated with a brown solid (copper)
62
What is electrolysis used for?
To make new substances
63
How does an electrolysis circuit become complete?
A flow of electrons taken from anodes to cathodes
64
How do you measure conductivity of an electrolyte?
With a conductivity probe
65
Why way do electrons flow in the circuit during electrolysis
Electrons flow from the anode to the cathode.
66
Why do most covalent compounds not conduct electricity?
Most covalent compounds do not conduct electricity because they have no freely moving ions to carry the current.
67
Why type of electrodes are typically used in electrolysis of molten compounds
Graphite or platinum
68
What determines the method of extraction of a metal?
The position of the metal on the reactivity series determines the method of extraction
69
Why is electrolysis used to extract metals above carbon in the reactivity series?
Electrolysis is used to extract metals above carbon in the reactivity series because they are too reactive to be reduced by carbon.
70
What is the main ore of aluminium?
The main ore of aluminium is bauxite, which contains aluminium oxide.
71
What is produced at the negative electrode during the extraction of aluminium oxide?
Aluminium is produced at the cathode during the extraction of aluminium.
72
What is produced at the positive electrode during the extraction of aluminium oxide?
Oxygen is produced at the anode during the extraction of aluminium.
73
What is the equation for the reaction at the anode in aluminium extraction?
The equation for the reaction at the anode in aluminium extraction is:
C(s) + 02(9) → CO2 (g)
74
Whations are always present in aqueous solutions?
Aqueous solutions always have H
and oH lon
present from the splitting of water molecules.
75
What are the products of electrolysis of acidified water?
The products of electrolysis of acidified water are hydrogen at the cathode and oxygen at the anode.
76
Why is electrolysis used to extract aluminium from its compounds?
Electrolysis is used to extract aluminium because:
Aluminium is very reactive and is high up in the reactivity series, above carbon.
This means it cannot be extracted by reduction with carbon.
So, electrolysis is needed to split aluminium oxide (Al₂O₃) into aluminium metal and oxygen using electricity.
77
Describe the electrolysis of aluminium oxide.
Aluminium oxide (Al₂O₃) is dissolved in molten cryolite to lower its melting point and reduce energy costs.
Electrolysis occurs in a molten (not aqueous) state so the ions can move freely.
At the Cathode (-):
Al³⁺ ions gain 3 electrons (reduction):
Al³⁺ + 3e⁻ → Al
Aluminium metal forms and sinks to the bottom.
At the Anode (+):
O²⁻ ions lose 2 electrons (oxidation):
2O²⁻ → O₂ + 4e⁻
Oxygen gas is released.
Extra Point:
The carbon anodes gradually burn away, reacting with oxygen to form carbon dioxide:
C + O₂ → CO₂
78
What are the products of the electrolysis of brine and a use for each?
At the Cathode (-):
Hydrogen gas (H₂)
Use: Making margarine (hydrogenation of oils)
At the Anode (+):
Chlorine gas (Cl₂)
Use: Disinfecting water / making bleach / PVC plastic
In Solution:
Sodium hydroxide (NaOH)
Use: Making soap / cleaning products
79
Explain the classification of the reactions at each electrode as oxidation or reduction.
At the Cathode (-):
Positive ions gain electrons
**This is reduction
At the Anode (+):
Negative ions lose electrons
**This is oxidation
80
What is ion
A charged particle formed when an atom gains or loses electrons.
81
What is Redox Reaction
A reaction in which both oxidation and reduction take place at the same time
82
What is a Discharge (of ions)
When ions gain or lose electrons to become neutral atoms or molecules at an electrode.
83
What is Electroplating
Using electrolysis to coat an object with a thin layer of metal.
84
What is a Molten Electrolyte
A melted ionic compound used in electrolysis so ions can move freely.
85
What is a Aqueous Solution
A solution where a substance (e.g. salt) is dissolved in water, introducing H⁺ and OH⁻ ions from water.
86
How is bauxite turned into aluminium oxide
It is purified.It is seperated from the ore which is bauxite.
