topic 4 chemical changes

Question 1

What is oxidation/reduction?

Answer 1

oxidation – when a substance gains oxygen
Reduction – when a substance loses oxygen

Question 2

how are unreactive metals found in earth?

Answer 2

In their natural state

Question 3

how can metals less reactive than carbon be extracted?

Answer 3

Reduction with carbon. Carbon displaced the metal in a metal oxides – oxidised carbon oxides. Metals from the metal oxide gets reduced to the pure metal.

Question 4

How are metals more reactive than carbon extracted?

Answer 4

Electrolysis

Question 5

how are oxidation and reduction defined in terms of electron transfer

Answer 5

oxidation – loss of electrons
Reduction – gain of electrons

Question 6

which metals in the reactivity series will react with an acid?

Answer 6

Those above hydrogen

Question 7

what is the general equation for a neutralisation reaction?

Answer 7

base + acid ——> salt + water 

Question 8

what is the general equation for the reaction between metal carbonate and an acid?

Answer 8

Metal carbonate + acid ——-> salt + water + carbon dioxide 

Question 9

What is the general equation for the reaction between metal oxides and acids?

Answer 9

Metal oxide + acid ——> a salt + water 

Question 10

What is a redox reaction?

Answer 10

Reaction were both oxidation and reduction occurs

Question 11

Explain in terms of gain or loss of electrons which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid

Answer 11

magnesium has lost electrons and this has been oxidised

The hydrogen in HCL has gained electrons and this means it has been reduced

Question 12

how is a soluble salt formed?

Answer 12

A-wrapped the excess acid with some insoluble chemical
B-filter off the leftovers
c-crystallised this product

Question 13

what do acids and alkalis produce in aqueous solutions?

Answer 13

Acids produce hydrogen ions, alkalis produce hydroxide ions

Question 14

What are bases, acids and alkalis?

Answer 14

bases are compounds that neutralise acids, acids produce hydrogen ions in acid solutions, alkalis a soluble bases – produce hydroxide ions in an aqueous solution

Question 15

What is the pH scale and what does a pH of seven show?

Answer 15

The measure of acidity/alkalinity of a solution: neutral solution

Question 16

State the general equation for a neutralisation reaction in a short, ionic form

Answer 16

H+ + OH- ——> H2O

Question 17

What is a strong acid and a weak acid?

Answer 17

strong acid is completely ionised in aqueous solutions; weak acid is only partially ionised in aqueous solution

Question 18

What happens to pH is concentration of H+ increases

Answer 18

The Ph decreases

Question 19

what is concentrated acid and what is a diluted acid? Is this the same as a strong and weak acid?

Answer 19

Concentrated acid has more moles of acid per unit volume than a dilute

It is not the same concentration is not the same thing as strength of an acid

Strength refers to whether the acid is completely ionised in water or only partially

Question 20

as the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?

Answer 20

Increased by a factor of 10

Question 21

what is electrolysis?

Answer 21

The passing of an electric current through ionic substance that are molten are in a solution to break them down into elements; ions discharged electro to produce these

Question 22

What is an electrolyte?

Answer 22

The liquid/solution which conduct electricity

Question 23

what is a cathode and what is a anode

Answer 23

cord is the negative electrode
anode is the positive electrode

Question 24

What occurs at the cathode and what occurs at the anode during electrolysis

Answer 24

reduction occurs at the cathode

Oxidation occurs at the anode

Question 25

In aqueous electrolysis, which element is discharge at the café? Oxygen is produced at the anode unless what

Answer 25

The less reactive element discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in case this said metal is produced. Oxygen is produced at the anode unless the solution contains halide ions in which case halogen molecules are produced. 

Question 26

how is aluminium manufactured? Why is it so expensive?

Answer 26

Aluminium is made through the electrolysis of aluminium oxide and croylite

Lots of energies needed to produce the current in electrolysis which makes this process expensive

Question 27

why is Cryolite used in manufacturing of aluminium?

Answer 27

It lowers the melting point of aluminium oxide, reducing energy costs