Electrochemistry

Question 1

Recognise it the oxidation states of metals

Answer 1

Zero oxidation state metals are solid metals
Positive oxidation state metals irons in solution
These ions are part of a salt

Question 2

Oxidation states of nonmetals

Answer 2

Zero oxidation state are non-metals as molecules
Positive or negative oxidation states are ions which are part of a salt in solution

Question 3

Strength of reducing agents

Answer 3

On the redox table on the extreme right side the reducing agents increase in reducing ability

Question 4

Strength of oxidising agents

Answer 4

On the redox table on the extreme left shows the increasing oxidising ability with the top being unreactive from lithium to calcium and very active from chromium to fluoride

Question 5

Spontaneous reactions C

Answer 5

Oxidation at the top, anode
Reduction at the bottom, cathode

Question 6

What does a half cell consist of

Answer 6

An electrode dipped into an electrical conducting solution

An element into different oxidation state

A suitable electrolyte is mostly nitric acid

Question 7

Electrode

Answer 7

A conductor through which electricity enters and leaves an object, substance or region

Question 8

Electrolytes

Answer 8

A substance that can conduct electricity by forming free ions when molten or dissolved in solution

Question 9

How do you gas half cells work

Answer 9

Gas hob cells consist of a gas in equilibrium with its ions
It is bubbled into the cell in a glass tube which has a piece of platinum in it
The gas absorbs onto the surface of the platinum foil
Remember the actual electrode is the platinum wire!

Question 10

Describe the standard hydrogen electrode and explain its role as the reference electrode

Answer 10

The standard hydrogen electrode is a hydrogen half cell which is assembled under standard conditions:
Concentration of one mole. DM3
Temperature: 25°C
Pressure: one ATM
It consists of hydrogen gas bubble through an electrolyte containing hydrogen ions under these conditions

Its role is that it is a reference electrode therefore its function It measures the EMF of the cell. The positive terminal of the volt meter is connected to the test cell and the negative terminal of the volt meter is connected to the she. The volt meter is set up assuming that the electron will flow from this she to the test cell. 

Question 11

Describe the galvanic cell in terms of:
Self-sustaining electrode reactions
Conversion of chemical energy to electrical energy

Answer 11

The governor excel is self-sustaining, in that the energy required for this side to operate comes directly from the chemical reactions within the cell itself.
The galvanic cells or voltaic cells convert chemical energy into electrical energy: Meaning as a result of these reactions as in one of the electrics have been negative and the other positive the electrons will flow from the negative electrode to the positive electrode and hence creates current

Question 12

Redox reactions in galvanic cells:
Predict the chemical species which is oxidise in a redox reaction and write an equation for the oxidation half reaction same for the reduction half reaction

Answer 12

One: identify the chemical species that is the stronger oxidising agent According to the redox tableThis means it will go under reduction And hence vice versa

Oxidation is the donation of electrons and hands it will decrease in mass while reduction is the exception of electrons and hence it will increase in mass

Question 13

The salt bridge:
What are the best salt to use in a salt bridge and why

Answer 13

The best Salts a group one nitrates which are KNO3, NANO3 or LIN03.
This is because group one ions are unreactive and will not compete for the electrons in a cell: nitrates only react if there is an acid present and neither of the ions forms precipitates
The electrolyte most of the news in the salt bridge is potassium nitrate

Question 14

What are the functions of a salt bridge

Answer 14

One: completing the circuit
To: maintaining electrical neutrality in the half cells:

Question 15

How does maintaining Electrical neutrality work with the salt bridge

Answer 15

Situation one: when anode ions are entering the electrolyte the balance between the cations and Anions is upset. There are now more anode ions then electrolyte irons In the electrolytes. This creates a buildup of positive charge and would make it more difficult For further anode ions to enter the electrolyte. In order to oppose the change the anions in the salt bridge, Viana irons in the salt bridge move out into the electrolyte or anode ions can move out of the electrolytes into the Salt bridge

Situation to: the cathode ions are removed from the cathode electrolyte hence there are more electrolyte ions then cathode ions in the electrolyte. This buildup of negative charge in the electrolyte would make it more difficult for further cathode ions to leave the electrolyte. To maintain the neutrality of the cathode electrolytes: Cat ions in the salt bridge move out of the salt bridge and into the cathode electrolyte or X says anions or salt from the electrolyte ions can move out of the electrolyte into the salt bridge. 

Question 16

Explain how standard electrode potentials can be determined in using the reference electrode and state the convention regarding positive and negative values

Answer 16

A half cell would be connected to this she at the positive terminal well that she is at the negative terminal. The negative sign tells us that ZN electrode is the anode and electrons flow from the Z electrode to the sheet. The reference electrode that she is assigned an E value of zero volts.

A positive sign tells us that the silver electrode is the cathode and electrons flow from the she to the silver electrode in the external circuits. Hence the silver ions are easily more reduced then hydrogen ions hence the silver half cell has a positive reduction potential. 

However if you calculate it use a positive value of standard EMF as an indication that the reaction is spontaneous understand it conditions

Question 17

Cell notation of a galvanic cell

Answer 17

Basic cell notation: no State symbols
Cell notation with state symbols: symbols are added
Cell notation with standard conditions: state symbols and standard conditions applied (state symbol before standard condition)

When both chemical species in a half cell are in the same Thursday are separated by a comma

Anode to cathode

Question 18

Cell notation with she

Answer 18

Always start with she
PT | H2 | H+

Question 19

Energy conversion in an electrolytic cell

Answer 19

From electrical energy to chemical energy

Question 20

The electrolysis of solution of copper ||chloride

Answer 20

Copper chloride dissociates in water in this equation: CuCl2(s)—> Cu^2+(aq) + 2Cl-(aq)

To inert electrodes are dipped into a copper chloride electrolyte and they DC power supply is connected to the two electrodes

The negative ions will be attracted to the positive electrode and the positive ions will be attracted to the negative electrode.The negative electrode is the cathode as it goes under reduction

Water is polar and his hands attracted to both of the electrodes
So hence there is a battle for dominance at each electrode

Question 21

The battle for dominance at each electrode in the electrolysis of copper chloride solution

Answer 21

At the negative electrode:
Both CU 2+ ions and water molecules are attracted to the cathode and will compete for electrons at the cathode. According to the redox table see you 2+ ions are the stronger oxidising agents and are therefore more easily reduced and hence Copper metal wall plates the surface of the cathode

At the positive electrode:
Both chloride ions and water molecules are attracted to the anode and Both have the ability to undergo oxidation. According to the redox table water molecules are slightly stronger reducing agents and hence a more easily oxidised and O2 will be produced at the anode however chloride irons are still produced at the anode

Question 22

Explain the role of concentration when predicting the predominant anode half reaction During electrolysis

Answer 22

If the concentration of this chloride irons is sufficiently high enough the chloride irons are oxidise in preference to the water molecules. This is because an increase in the concentration of chloride molecules will increase the oxidation potential of the Chloride ions so that it is greater than the oxidation potential of water

Question 23

What will determine which half reaction will be predominant at the cathode

Answer 23

It is the inherent reactivity (electrode potential/strength of agents)

Question 24

Why is it not possible to electroplate using metal ions which are weaker oxidising agents then water under standard conditions

Answer 24

Since at the anode the metal chosen is about to be electroplated if the oxidising agent is weakerThen the substance that supposed to be plating the object from the cathode will predominantly be water

Question 25

Under what circumstances will the anode itself will be oxidised in preference to the irons in the solution

Answer 25

If they swapped the sides of the DC battery

Question 26

Explain the electro refining of copper including the possible competitive reactions that can take place at the electrodes due to the presence of impurities

Answer 26

Impure copper or, known as blister copper is made the anode
A small metal sheet of pure copper is attached as the cathode
And electrolyte of copper sulphate is used in the electrolytic cell. Once again the electrolyte must contain metal ion and substance that is being refined.

At the cathode: the copper ions and water molecules are attracted to the negatively charged cathode. According to the redox table, copper ions are stronger oxidising agents then water therefore copper ions are reduced to copper atoms at the cathode.

At the anode copper atoms are stronger reducing agent then the water molecules and sulphate anions. Copper atoms are present in the impure copper or will be oxidised to copper ions at the anode.

The blister copper contains other more active metals such as iron, nickel, zinc, cobalt, Tim there are also oxidised at the anode, they become cations and go into the solution. These cations remain in the solution because they are weaker oxidising agents then the copper irons. The copper ions are more easily reduced at the cathode.

Less active metals in the impure sample such asSilver, gold, and platinum. Do not oxidised at the anode but instead collect as a sludge underneath the anode to be collected and for the process to recover these valuable metals.

Question 27

What is electro refining

Answer 27

The process of refining a metal in an electrolytic cell. And M pure metal is used as the anode and the refine metal is deposited at the cathode. 

Question 28

The Hall-Harolt process
Industrial extraction of aluminium

Answer 28

Bauxite it is crushed and aluminium oxide (alumina) is extracted from the bauxite. Alumina is a white powder put the formula AL203. In order to extract the alumina from the alumina, the alumina is electrolyseD. However in doing so we come across a few problems:

Problem one: in order for electrolysis to occur, the a L3 plus ions must be mobile. Alumina is not soluble in water and melting takes too much power. This problem is solved by dissolving the alumina in liquid cryolite. Cryolite is a salt with formula NA3ALF6. The cryolite is melted with a lower temperature, and the alumina is dissolved.

Problem to: we now have the following ions in the mixture: AL3 plus, N a plus, 02 minus, F minus. We need the a Al3+ to be reduced. The Malton alumina/cryolite mixture is placed in a reaction vessel and carbon electrodes are lowered into the note. These carbon electrodes are connected to the positive terminal of a power supply making the anode positive. The graphite line tank is connected to the negative terminal of the power supply making the tank the negative cathode. Therefore the Mount contains the following ions: a L3 plus, 02 minus, sodium and F.

At the cathode: L3 plus ions in the melt are reduced to a L atoms. The Malton AL Kalex at the bottom of the tank and is removed. This is due to the fact that sodium cations in the cryolite are weaker oxidising agents then aluminium ions

At the anode: oxide ions in the Mount oxidise 202 gas at the anode. This is because fluoride ions in the chrysolite are weaker than the reducing agent then oxygen ions.

Problem three: only electrolysis is complete, there is a secondary unfavourable reaction. The oxygen which is formed reacts with the carbon electrodes. Oxygen gas reacts with carbon electrodes to form carbon dioxide gas. Because of this the carbon electrodes corrode and must be replaced from time to time

Question 29

Alumina am is the most abundant metal on Earth why is it so expensive

Answer 29

The process of extracting aluminium is expensive

Question 30

What are the potential environmental risks of aluminium Extraction

Answer 30

The process consumes large quantities of electrical energy making the production of alumina expensive

The carbon dioxide produced at the carbon dioxide is released into the atmosphere. Carbon emissions can be as high as 16 tons of carbon dioxide per ton of alumina am produced. Carbon dioxide is a greenhouse gas which can cause global warming

The process produces fluoride waste and omissions which are toxic to vegetation: a greenhouse gases and are harmful to human health.
Recycling of alumina am product is highly desirable as it is far cheaper to recycle the metal Then to manufacture it. Recycling alumina reduces energy consumption, harmful emissions, Litter et cetera

Question 31

Chlor alkali

Answer 31

Sodium chloride is electrolysed to yield three lucrative products: hydrogen gas, oil and gas, and sodium hydroxide

At the anode (negative): Chlorine ion is very concentrated and will hands be oxidised instead of water
At the cathode (positive) water will be the stronger oxidising agent LOL hence go under reduction.

However we still bump into various issues:
One: the hydrogen and the chlorine gas that are formed need to be kept separate this is so that they can be sold in appeal form and also because they react explosively if they mixed together.
To: the hydroxide ions remain in the solution with the sodium ions hence forming a sodium hydroxide. This product is mixed with unreacted sodium chloride which would mean that Pure sodium hydroxide is not formed as it is mixed with sodium chloride. This reduce the value of sodium hydroxide. Hence we need to separate sodium hydroxide from the sodium chloride. Remember the concentration of sodium chloride has to be kept at a higher level so that the chloride ions will be oxidised instead of water.

There are different ways to avoid this which will come in from of the mercury cell, the diaphragm cell and the membrane cell

Question 32

The Mercury cell

Answer 32

Know the diagram
At the anode (positive): large graphite rods are connected to the positive terminal of the power source. The roads become the anode of the cell. The rather dipped into the concentrated sodium chloride solution (brown). Chloride ions are oxidised to form chlorine gas

At the cathode (negative) the stainless steel base of the container is connected to the negative terminal of the power source. The cathode is a shallow layer of mercury which flows across the stainless steel base of the container. As it flows across the best to make you becomes negatively charged and X as the cathode itself. Sodium ions in the brei not attracted to the cathode and are reduced to sodium atoms.

The mercury so requires a voltage between 3V and 4V. This voltage is needed to ensure that the sodium ions are reduced at the cathode instead of water ions.

When the sodium metal is dissolved into the macular it forms a sodium mercury a muggle am
The sodium or mercury amalgam flows out of the electrolyser into the decomposer which contains water. The sodium metal reacts with water to form aqueous sodium hydroxide and hydrogen gas. The mercury that is now left behind is recycled back into the electrolyser

Question 33

Sodium mercury amalgam

Answer 33

A mixture of mercury and sodium metals (an alloy of mercury)

Question 34

Advantages of the mercury cell

Answer 34

One: a relatively high percentage purity of sodium hydroxide is obtained (50%) because the sodium hydroxide is separate from the brain.
To code on it also allows chlorine and hydrogen to be formed in separate areas. Chlorine and hydrogen can combine explosively if they met.

Question 35

Disadvantages of the mercury cell

Answer 35

One: the mercury cell is more expensive to build , Run and maintain then the other cells.
To: there is a fairly high level of mercury contamination in the sodium hydroxide solution and hydrogen gas leaving the cell. Mercury is highly toxic causing sodium hydroxide and hydrogen to be purified before they can be used which is expensive.
The toxicity of make we can cause environmental concerns at the deposal of waste Mercury is extremely hazardous
Three: the Mercury can pass along the food chain with concentration and provide along the way. This result can result into consumers receiving a dose of mercury which can affect the nervous system, leading to brain damage.

This has resulted in a limitation based on the amount of make you discharge with a limit of 1 g per ton of sodium hydroxide produced. This means that fewer battery cells are being built

Question 36

The diaphragm cell

Answer 36

It has two chambers, and an awake compartments and they castaway compartment separated by permeable asbestos diagram. The permeable diaphragm allows ions to move from one compartment to the other but prevents the mixing of gases produced at the electrodes.

At the anode (positive): chloride irons in the Briner oxidised to chlorine gas at the anode

At the cathode (negative): water molecules are reduced at the cathode. Hydrogen gas and hydroxide ions are produced.

The electrolyte in the anode compartment is kept at a higher level than the cathode compartment. This verse is the solution to flow into the cathode reducing the flow of hydroxide irons into the diaphragm catfood to the anode minimising contact between chlorine and hydroxide irons which from unwonted chloride irons.

Porous Our material containing pause barrier is the diaphragm between the anode and cathode compartments intended to allow sodium ions to flow through To balance the charge of hydroxide ions formed and complete the flow of electricity in the circuit, also allowing a buildup of sodium hydroxide ions in the cathode compartment. The diaphragm is made out of us pestos, which is not damaged by the hydroxide solution

The voltage across the lectures is 3.5 till five vaults

Dissolution taken at the end has both sodium hydroxide and sodium chloride. Water is evaporated from the solution until the message is 50% of sodium hydroxide. At this stage, most of the sodium chloride has crystallised so I can be filter off and the solution of nearly pure sodium hydroxide can be solid or evaporated to joiners to produce solid sodium hydroxide the product contains 1 to 2% NaCl

Question 37

Advantages of the diaphragm so

Answer 37

Large quantities of sodium hydroxide in the chlorine can be produced, which are too high demand industrial chemicals, at reasonable cost and had quite acceptable levels of purity

Question 38

The disadvantages of Diaphragm cell

Answer 38

One: there is always a small amount of chloride in the sodium hydroxide produce.
To: there are health and environmental problems with small losses of asbestos in making and using diaphragms. Asbestos is carcinogenic a.k.a. causes cancer
Three: diaphragm is none ion selective, so the control iron movements is limited.

Question 39

The membrane cell

Answer 39

The cell relies on an iron exchange membrane to separate sodium ions and chloride ions in the brain. This membrane is made from polytetrafluoroethylene (PTFE), making it a plastic membrane, which has been modified to include an ionic groups to act as an iron exchange membrane.This allows sodium ions to pass through it but not chloride irons or hydroxide irons.

There are no dick compartment is filled with the brand solution. The fresh Brian is continually fed into the end no dick department to ensure a high concentration of chloride ions.

At the anode (positive) chloride ions in the Briner oxidised to form chlorine gas at the anode
Pure water is continually fed into the Catholic department. SodiumMolecules are reduced at the cathode

Question 40

Advantages of the membrane cell

Answer 40

There is no byproduct of the sodium chloride due to the membrane preventing the chloride and hydroxide ions to pass through
The use of this process results in virtually pure sodium hydroxide being produced (only contains about 0.02% of sodium chloride at most) as there is no contamination by the chloride irons

There is very little harm full impact on the environment as the membrane is environmentally friendly
It is cheaper to run the membranes are compare to other cells

Question 41

Disadvantages of the membrane cell

Answer 41

Plastic litter

Question 42

Similarities between the diaphragm cell and the membrane cell

Answer 42

One: separate anodic and Catholic compartment
To: chlorine gas produced in the an anodic compartments. Hydrogen gas and the sodium hydroxide solution formed in the cathode compartment.
Three: compartments are separated from each other by diaphragm

Question 43

Differences between the diaphragm cell in the membrane cell

Answer 43

Well in diaphragm both compartments contain Brian, in the membrane cell Brian this fit into the anodic department. Water is Vernon to the cathodic compartment

While electrolyte levels are different in each compartment in the diaphragm cell, the levels are the same in the membrane cell

While non-iron selective of space those diaphragm is in the diaphragm cell, fluoropolymer iron exchange membrane is in the membrane cell which does not allow chlorine or Hydroxide ions to pass through

Question 44

What are the uses of chlorine in the claw alkali industry

Answer 44

One: coin act as a disinfectant by killing bacteria in drinking water and swimming pools
To: it is used to make bleach
Three: used to make Disinfectant
Four: used to make PVC plastics
Five: used to manufacture of hydrochloric acid
Six: use to make CFC is which are now mostly banned

Question 45

The uses of hydrogen in the chloralkali industry

Answer 45

One: in the harbour process to form ammonia = fertiliser Industry
2: used in the manufacturing of margarine

Question 46

What are the uses of sodium hydroxide in the chloralkali industry

Answer 46

One: used in the manufacturing of soaps.
To: used in the production of paper
Three: use in making ceramics
Four: Using making Drain cleaners

Question 47

The environmental impact of the chloralkali industry

Answer 47

Hydrogen gas is highly flammable and can react explosively
Chlorine gas is highly toxic which can cause severe damage to lungs
Sodium hydroxide is highly corrosive and toxic
The structure of the cells can potentially result in severe environmental safety problems:
Mercury use in the making salt can cause irreparable damage to the central nervous system
Asbestos found in the diaphragm cell is a dangerous carcinogen and cause severe respiratory disease called asbestosis