Electrolysis Flashcards
Category: Components of an Electrolytic Cell
In a battery, which terminal receives electrons from which electrode?
(+) terminal receives electrons from anode.
(-) terminal supplies electrons to cathode.
Category: Components of an Electrolytic Cell
What states must the electrolyte be in and why?
The molten or aqueous state. In such solutions, ions are not held in fixed positions throughout the structure and are hence free to move around. As a result, these mobile ions act as charge carriers, conducting electricity through the solution and throughout the entire circuit.
On the other hand, in the solid state, these ions are held in fixed positions by strong electrostatic forces of attraction. Due to the absence of mobile ions, electricity is unable to be conducted throughout the circuit.
Category: Components of an Electrolytic Cell
What form of redox reaction occurs at what electrodes:
(An Ox): Oxidation occurs at the anode.
(Red Cat): Reduction occurs at the cathode.
Oxidation refers to the increase in oxidation state, while reduction refers to the decrease in oxidation state.
Category: Electrolysis of Molten Electrolytes
What happens during the process of electrolysis of molten electrolytes?
Molten electrolytes are typically ionic compounds in the molten state. meaning that they are binary, containing a metal cation and a non-metal anion.
As a result, during electrolysis, such binary compounds undergoes electrolysis, resulting in the formation of a metal and a non-metal (typically a gas).
Category: Electrolysis of Aqueous Electrolytes
What happens during the process of electrolysis of aqueous electrolytes?
In an aqueous solution of ionic compounds, water is present, meaning that aside from the cations and anions from the ionic compound, there are also H+ and OH- ions present.
As a result, due to there being two cations and two anions competing to be discharged at the electrodes, selective discharge of ions would occur, with the ion that is easier to discharge being oxidised/reduced preferentially.
Category: Electrolysis of Aqueous Electrolytes
How are the cations selectively discharged?
The table of selective discharge: The more reactive an element is, the more difficult for it to be discharge. As a result, every element above Hydrogen in the table would not be selectively oxidised or reduced first.
Ranking the elements from most reactive to least reactive:
1) Potassium
2) Sodium
3) Calcium
4) Magnesium
5) Zinc
6) Iron
7) Lead
8) Hydrogen
9) Copper
10) Silver
Category: Electrolysis of Aqueous Electrolytes
How are anions selectively discharged? Based on what?
Based on the table of ease of discharge of anions: In this table, the anions are ranked from the most difficult to discharge to the easiest to discharge.
1) Sulfate anions
2) Nitrate anions
3) Chloride anions
4) Bromide anions
5) Iodide anions
6) Hydroxide anions.
Hence, hydroxide anions would be selectively oxidised over each and every one of the above anions.
Category: Electrolysis of Aqueous Electrolytes
How does anion concentration affect selective discharge of anions?
The higher the concentration of anions, the more likely it will be oxidised at the electrode.
Note: Fluoride, nitrate and sulfate ions are anions with very low priority or tendency of being oxidised at the anode. They are usually not oxidised even in aqueous solutions.
Category: Predicting the product of an aqueous solution
What are the steps to predict the product formed after the electrolysis of an aqueous solution?
- Determine the ions present in the electrolyte. Note that H2O is present.
- Compare the relative position of the competing ions/species in the electrochemical series. The species that is lower in the electrochemical series would be preferentially discharged.
- If the concentration is high, it may be preferentially discharged despite being higher in the electrochemical series.
- If active electrodes are used, the metal in the anode may be selectively oxidised.
Category: Predicting the product of an aqueous solution
What is the electrochemical series for cathode?
- K+
- Ca2+
- Na+
- Mg2+
- Al 3+
- 2H2O
- Zn2+
- Fe2+
- Sn2+
- H+
- Cu2+
- Ag+
Category: Predicting the product of an aqueous solution
What is the electrochemical series for anodes?
- Fluoride ion
- Sulfate ion
- Chloride ion
- Water (H2O)
- Bromide ion
- Iodide ion
- Hydroxide ion
Category: Simple Cells
What are simple cells?
Simple cells are cells which consist of two electrodes made of metals with differing reactivity。
Category: Simple Cells
How does one distinguish which metal is which electrode?
Metals higher up in the reactivity series have a greater tendency to lose electrons.
Thus, the anode is the more reactive metal while the cathode is the less reactive metal.
Category: Simple cells
What is the relationship of the voltage with the difference in reactivity of the metals?
The further apart the metals are in the metal reactivity series, the higher the voltage produced by the simple cell.
Category: Electrolysis using reactive electrodes
What is electrolysis using reactive electrodes and which electrode does it affect?
It is when electrodes are made of materials other than platinum and graphite, and are known as reactive.
It only affects the reaction at the anode. If the anode is a reactive electrode, the anode will be oxidised selectively, preferentially discharged over the anion attracted to the anode.
Example: When copper(II) sulfate is electrolysed using reactive copper electrodes, the reactive copper electrode is selectively oxidised at the anode.
