electricity and chemistry

Question 1

Electrode is…

Electrolyte is…

Anode …

Anion is…

Cathode is…

Cation is…

Answer 1

1. a rod of metal or graphite through which an electric current flows into or out of an electrolyte.
2. the ionic compound in molten or dissolved solution that conducts the electricity.
3. is the positive electrode of an electrolysis cell.
4. a negatively charged ion which is attracted to the anode.
5. the negative electrode of an electrolysis cell.
6. a positively charged ion which is attracted to the cathode.

Question 3

Define electrolysis as

Answer 3

the breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity

Question 4

When an electric current is passed through a molten ionic compound the compound

Answer 4

decomposes or breaks down.

Question 5

When an electric current is passed through a molten ionic compound or… f ionic compounds decompose

Answer 5

aqueous solutions

Question 7

Covalent compounds cannot

Answer 7

conduct electricity hence they do not undergo electrolysis.

Question 8

Ionic compounds in the …cannot conduct electricity either since they have no free…that can move and carry the charge.

Answer 8

• solid state
• ions

Question 9

draw electrical conductivity of ionic compounds when in the solid state and in molten or aqueos solution

Answer 9

Question 10

PANIC

Answer 10

Positive (is) Anode Negative Is Cathode.

Question 11

Answer 11

Question 12

Electrolysis of Molten Compounds e.g: Lead (II) Bromide:

DRAW a Diagram Showing the Electrolysis of Lead (II) Bromide

Answer 12

Question 13

Electrolysis of Molten Compounds e.g: Lead (II) Bromide:

mthod and reaction at the electrodes

Answer 13

Method:

Add Lead (II) Bromide into a beaker and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge.

Add two graphite rods as the electrodes and connect this to a power pack or battery.

Turn on power pack or battery and allow electrolysis to take place.

Negative bromide ions move to the positive electrode (anode) and lose two electrons to form bromine molecules. There is bubbling at the anode as brown bromine gas is given off.

Positive lead ions move to the negative electrode (cathode) and gain electrons to form a grey lead metal which deposits on the surface of the electrode.

Reaction at Electrodes:

Question 14

Electrolysis of Aqueous Solutions

general Rules

Answer 14

Aqueous solutions will always have water (H2O).

H+ and OH– ions from the water are involved as well.

Question 15

rules Positive Electrode (anode)

Answer 15

OH– ions and non-metal ions attracted to positive electrode.

Either OH– or non-metal ions will lose electrons and oxygen gas or gas of non-metal in question is released E.g. Chlorine, Bromine, Nitrogen.

The product formed depends on which ion loses electrons more readily, with the more reactive ion remaining in solution. A reactivity series of anions is shown below:

More reactive SO42- → NO3– → OH– → Cl– → Br– → I– Less reactive

Question 16

rules Negative Electrode (cathode)

Answer 16

H+ and metal ions attracted to the negative electrode but only one will gain electrons.

Either hydrogen or metal will be produced.

If the metal is above hydrogen in reactivity series, then hydrogen will be produced and bubbling will be seen at the cathode.

Question 17

rules Concentrated and dilute solutions

Answer 17

Concentrated and dilute solutions of the same compound give different products.

For anions, the more concentrated ion will tend to get discharged over a more dilute ion.

Question 18

Electrolysis of binary molten compound

Answer 18

For a binary molten compound of a metal and a nonmetal, the cathode product will always be the metal.

The product formed at the anode will always be the non-metal.

Method:

Add aqueous solution into a beaker.

Add two Graphite rods as the electrodes and connect this to a power pack or battery.

Turn on power pack or battery and allow electrolysis to take place.

Reaction at Electrodes:

Question 19

Reaction at Electrodes:

Answer 19

Question 20

Determining what Gas is Produced

Answer 20

If the gas produced at the cathode burns with a ‘pop’ when a sample is lit with a lighted splint then the gas is hydrogen.

If the gas produced at the anode relights a glowing splint dipped into a sample of the gas then the gas is oxygen.

The halogen gases all produce their own colours (bromine is red-brown, chlorine is yellow-green and fluorine is pale yellow).

Question 21

Copper refining

Answer 21

The electrolysis of CuSO4 using graphite rods produces oxygen and copper.

By changing the electrodes from graphite to pure and impure copper, the products can be changed at each electrode.

Electrolysis can be used to purify metals by separating them from their impurities.

In the set-up, the impure metal is always the anode, in this case the impure copper.

The cathode is a thin sheet of pure

The electrolyte used is an aqueous solution of a soluble salt of the pure metal at the anode, e.g: CuSO4.

Copper atoms at the anode lose electrons, go into solution as ions and are attracted to the cathode where they gain electrons and form now purified copper atoms.

The anode thus becomes thinner due to loss of atoms and the impurities fall to the bottom of the cell as sludge.

The cathode gradually becomes thicker.

Question 22

Electrolysis of halide solutions

Answer 22

We have seen that cations that are lower down on the reactivity series tend to be discharged in preference to more reactive cations.

The same occurs for anions which can be arranged in order of ease of discharge:

More reactive SO42- → NO3– → OH– → Cl– → Br– → I– Less reactive

E.g: in a concentrated aqueous solution of barium chloride, the Cl– ions are discharged more readily than the OH– ions, so chlorine gas is produced at the anode.

If the solution is dilute however only the OH– ion is discharged and so oxygen would be formed.

Question 23

Transfer of charge

Answer 23

During electrolysis the electrons move from the power supply towards the cathode.

Positive ions within the electrolyte move towards the negatively charged electrode which is the cathode.

Here they accept electrons from the cathode and either a metal or hydrogen gas is produced.

Negative ions within the electrolyte move towards the positively charged electrode which is the anode.

If the anode is inert (such as graphite or platinum), the ions lose electrons to the anode and form a nonmetal or oxygen gas.

If the anode is a reactive metal, then the metal atoms of the anode lose electrons and go into solution as ions, thinning the anode.

Question 24

When a metal conducts it is the … that are moving through the metal.

Answer 24

elctrons

Question 25

When a salt solution conducts it is the …in the solution that move towards the electrodes carrying the electrons.

Answer 25

ions

Question 26

whta happens at the cathode

Answer 26

Reduction occurs at the cathode as the positive ions gain electrons.

Question 27

Answer 27

Question 28

Electrochemical cells

Answer 28

An electrochemical cell is a source of electrical energy.

The simplest design consists of two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external circuit.

A common example is zinc and copper.

Zinc is the more reactive metal and forms ions more easily, releasing electrons as its atoms form ions.

The electrons give the more reactive electrode a negative charge and they then flow around the circuit to the copper electrode.

The difference in the ability of the electrodes to release electrons causes a voltage to be produced.

The greater the difference in the metal’s reactivity then the greater the voltage.

Question 29

During electrolysis oxidation of the …ions always occurs at the… and reduction of the metal or …ions occurs at the ….

Answer 29

• non metal
• anode
• hydrogen
• cathode.

Question 30

Describe the electroplating of metals

Answer 30

this is a process where the surface of one metal is coated with a layer of a different metal.

The metal being used to coat is a less reactive metal than the one it is covering.

The anode is made from the pure metal used to coat.

The cathode is the object to be electroplated.

The electrolyte is an aqueous solution of a soluble salt of the pure metal at the anode.

Question 32

Uses of Electroplating

Answer 32

Electroplating is done to make metals more resistant to corrosion or damage, e.g: chromium and nickel plating.

It is also done to improve the appearance of metals, e.g: silver plating cutlery.

Question 33

Conductors

Answer 33

Conductors of electricity allow electrical charge to pass through them easily.

Conductors can be:

Solids such as metals or graphite.

Liquids such as molten lead bromide or molten metals.

Solutions such as sodium chloride solution.

Copper is used extensively in electrical wiring as it is an excellent conductor and is malleable and easy to work with.

Aluminium is used in overhead cables which are reinforced with a steel core.

The steel core provides extra strength and prevents the cable from breaking under its own weight.

Although not as good a conductor as copper, it is less dense and cheaper than copper.

Insulators

Question 34

Insulators

Answer 34

Insulators resist the flow of electricity and do not conduct.

Most insulators are solids of plastic, rubber or ceramic.

Plastics are used as insulators and are placed around electrical wiring and for some tool and machine handles.

Ceramics are used in very high voltage lines where contact between the power line and the metal of the pylon would be dangerous.

Question 36

The Earth’s Crust contains…such as Gold, Iron Oxide and Aluminium Oxide,but when found in the Earth, these are often…

Answer 36

• metals and metal compounds
• mixed with other substances.

Question 37

To be useful, the metals have to be extracted from their ore through processes such as…

Answer 37

electrolysis, using a blast furnace or by reacting with more reactive material.

Question 38

Metals which lie above … have to be extracted by… as they are too…

Answer 38

• carbon
• electrolysis
• reactive.

Question 40

Extraction of aluminium

Answer 40

Raw Materials:

Aluminium Ore (Bauxite)

Explanation:

The Bauxite is first purified to produce Aluminium Oxide Al2O3

Aluminium Oxide has a very high melting point so it is first dissolved in molten Cryolite, producing an electrolyte, which:

has a lower melting point

is a better conductor of electricity than molten aluminium oxide

reduces expense considerably

The electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000 °C.

The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell.

The cell operates at 5-6 volts and with a current of 100,000 amps.

The heat generated by the huge current keeps the electrolyte molten.

A lot of electricity is required for this process of extraction, this is a major expense

Reaction at the Negative Electrode:

The Aluminium melts and collects at the bottom of the cell and is then tapped off:

Al3+ + 3e– → Al

Reaction at the Positive Electrode:

2O2- – 4e– → O2

Some of the Oxygen Produced at the positive electrode then reacts with the Graphite (Carbon) electrode to produce Carbon Dioxide Gas:

C (s) + O2 (g) → CO2 (g)

*This causes the carbon anodes to burn away, so they must be replaced regularly.

Question 41

Manufacture of chlorine, hydrogen and sodium hydroxide

Answer 41

Brine is a concentrated solution of aqueous sodium chloride.

When electrolysed it produces chlorine, hydrogen and sodium hydroxide.

The electrolyte is concentrated sodium chloride which contains the following ions: H+, Cl– and OH–.

The H+ ions are discharged at the cathode as hydrogen gas.

The Cl– ions are discharged at the anode as chlorine gas.

The Na+ and OH– ions remain behind and form the NaOH solution.