Chp 5 - Electricity And Chemistry

Question 1

What is electrolysis

Answer 1

When an electric current is passed through a molten ionic compound the compound decomposes or breaks down into its non ion state.

The process also occurs for aqueous solutions of ionic compounds
Ask teacher

Question 2

Why do covalent compounds not undergo electrolysis

Answer 2

It’s because covalent compounds cannot conduct electricity hence they do not undergo electrolysis

Question 3

Can ionic compounds conduct electricity in a solid state

Answer 3

Ionic compounds in the solid state cannot conduct electricity either since they have no free ions that can move and carry the charge

Question 4

What is an electrode

Answer 4

its a rod of metal or graphite through which an electric current flows into or out of an electrolyte

Question 5

What’s an electrolyte

Answer 5

Its the ionic compound in molten or dissolved solution that conducts the electricity.

Question 6

What’s the anode

Answer 6

It’s the positive electrode of an electrolysis cell

It’s where anions go to

Question 7

What’s an anion

Answer 7

An anion is a negatively charged ion which is attracted to the anode

Question 8

What’s a cathode

Answer 8

A cathode is the negative electrode of an electrolysis cell

It attracts cations

Question 9

What is a cation

Answer 9

A cation is a positively charged ion which is attracted to the cathode

Question 10

For example in the electrolysis of lead bromide what happens

Answer 10

First 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 .

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

Question 11

What do electrolysis in aqueous solutions always have

Answer 11

Aqueous solutions will always have water (H2O)

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

Question 12

For a reaction in aqueous solutions what’s most likely to happen

Answer 12

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.

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 13

In electrolysis who goes first to give or take electrons to return back to its original form

Answer 13

The less reactive one does

Question 14

What is the reactivity series

Answer 14

Potassium, sodium, lithium, calcium, magnesium, aluminium, CARBON, zinc, iron, HYDROGEN, copper, silver, gold

Or group 1, group 2, group 3, CARBON, zinc, iron, HYDROGEN, copper, silver, gold

Question 15

What’s the difference between concentrated solution and dilute situation

Answer 15

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.
Ask teacher

Question 16

What does binary compound mean

Answer 16

A compound consisting of only 2 elements

Question 17

When you have a binary compound that’s metal and non metal during electrolysis where do they go

Answer 17

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 which is anion

Question 18

In electrolysis what happens with concentrated sodium chloride which is an aqueous solution
Ions from Nacl: Na+ Cl-
Ions from H2O: H+ OH-

Answer 18

Anode reaction: 2CL —> CL2 + 2e-
Chlorine gas is released as it’s lost enough electrons to become chlorine again it’s original form

Cathode reaction: (2H+) + (2e-)—> H2
Hydrogen gas is released as it gains enough electrons each back to become its normal form again.

Ask teacher why they turn into gases

Question 19

When looking at a chemical reaction what way do you look first to see the reactant and product

Answer 19

You go from left to right
E.g 2CL —> CL2 + 2e
You go from left to right meaning that the end result is that chloride loses its 2 electrons to become a gas again
E.g 2H + 2e —> H2
You go from left to right meaning that the end result becomes a hydrogen gas but it gains electrons again to become one

Question 20

What happens to the solution dilute sodium chloride in electrolysis
Ions from NaCl : Na + Cl-
Ions from H20 : (H+) + (OH-)

Answer 20

Anode reaction:
(4OH-) —> O2 + H2O + 4e-
Oxygen is produced

Cathode reaction:
2H + (2e-) —> H2
Hydrogen gas is produced
Ask teacher how this works

Question 21

Describe a chemical test for water

Answer 21

Anhydrous copper sulphate

It’s originally white but when it reacts with water it turns blue

White —> blue

Question 22

How do you determine what gas is produce at an electrode

Answer 22

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 23

What do you do to copper refine CuSO4

Answer 23

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 copper

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 24

How can you purify metals in electrolysis

Answer 24

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

Question 25

How do anions work in terms of being first to give or take electrons

Answer 25

We have seen that cations 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

However if the solution is dilute only the OH– ion is discharged and so oxygen would be formed

Question 26

In the cathode what is normally produced

Answer 26

either a metal or hydrogen gas is produced

Question 27

What’s the difference between an inert anode and reactive anode

Answer 27

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 28

In electrolysis state what this equation is:

Pb2 + 2e- —> Pb

Answer 28

Reduction occurs at the cathode as the positive ions gain electrons to become a normal element

Question 29

What’s an electrochemical cell

Answer 29

An electrochemical cell is a source of electrical energy

Question 30

Give an example of how electrochemical cells work

Answer 30

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
Ask teacher

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

The greater the difference in the metals’ reactivity, the greater the voltage

Question 31

How is voltage produced in electrolysis

Answer 31

It’s produced by the difference in reactivity of electrodes

Question 32

When a metal conducts it is the electrons that are moving through the metal. What happens if a salt solution conducts in electrolysis

Answer 32

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

Question 33

What is electroplating

Answer 33

Electroplating 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 that was 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 34

What are the uses of electroplating

Answer 34

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 35

What are conductors

Answer 35

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

Question 36

What are insulators

Answer 36

Insulators are the opposite of conductors as they 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 37

In earths crust are metals and metal compounds such as gold, iron oxide, aluminium oxide.
But when found these substances are often mixed with it her substances.
How do people extract the metal from the other substance

Answer 37

metals have to be extracted from their ore through processes such as electrolysis, using a blast furnace or by reacting with more reactive material
Metals which lie above carbon have to be extracted by electrolysis as they are too reactive

Question 38

When metals are too reactive what do you do

Answer 38

Metals which lie above carbon in the reactivity scale have to be extracted by electrolysis as they are too reactive

Question 39

How are potassium, sodium, lithium, calcium, magnesium, aluminium, carbon extracted

Answer 39

metals are extracted by electrolysis of molten chloride or molten oxide

This is a very expensive process though

Question 40

How are zinc, iron, hydrogen and copper extracted

Answer 40

They are extracted by heating with a reducing agent( gives electrons to another element and that element gets reduced while the reducing agent gets oxidised) such as carbon such as carbon or carbon monoxide in a blast furnace

This is a cheap process as carbon is cheap and can also be used as a heat source

Question 41

Do silver and gold need to be extracted

Answer 41

No they don’t as they are found as pure elements

Question 42

What is cryolite used for

Answer 42

It’s used for dissolving of substances in electrolysis.

It acts an electrolyte with an other substance that has dissolve in its molten state.

Question 43

What is bauxite

Answer 43

Aluminium ore

Question 44

What’s the difference between 2O and O2

Answer 44

2O is the ion state of oxygen whereas O2 is the free natural gas state of oxygen

Question 45

Why can carbon dioxide be produced in electrolysis

Answer 45

It’s can happen as some of the Oxygen Produced at the positive electrode (anode) can react with a Graphite (Carbon) electrode to produce Carbon Dioxide Gas:

C (s) + O2 (g) → CO2 (g)

This is what causes the graphite anodes to burn away so they must be reduced regularly

Question 46

What is brine and how is the manufacture of chlorine, hydrogen and sodium hydroxide done

Answer 46

Brine is a concentrated solution of aqueous sodium chloride
When electrolysed it produces chlorine, hydrogen and sodium hydroxide

The electrolyte is a 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

In the end the electrolyte turns into a sodium hydroxide solution:
NaOH