Chemical Changes

Question 1

What is oxidation?

Answer 1

When a substance gains oxygen and loses electrons

Question 2

What is reduction?

Answer 2

When a substance loses oxygen and gains electrons

Question 3

What is the reactivity of metals?

Answer 3

The series shows the metals in order of their reactivity

Question 4

What is a displacement reaction?

Answer 4

A reaction where a more reactive metal displaces a less reactive metal from a compound

Question 5

How are unreactive metals found in Earth?

Answer 5

In their natural state

Question 6

How can metals less reactive than carbon be extracted?

Answer 6

Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal

Question 7

How are metals more reactive than carbon extracted?

Answer 7

By electrolysis

Question 8

What is the general equation for a reaction between metals and acids? What type of reaction is this?

Answer 8

Metal + acid —> salt + hydrogen
Redox reaction, also a displacement reaction

Question 9

Which metals in the reactivity series will react with acid?

Answer 9

Those above hydrogen

Question 10

What is the general equation for a neutralisation reaction?

Answer 10

Base + acid —> salt + water

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Metal oxide + acid —> salt + water

Question 13

What is a redox reaction?

Answer 13

A reaction where both oxidation and reduction occurs

Question 14

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 14

-Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)
-The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H2)

Question 15

How is a soluble salt formed?

Answer 15

• React the excess acid with some insoluble chemical
• Filter off the leftovers
• Crystallise the product

Question 16

What do acids and alkalis produce in aqueous solutions?

Answer 16

Acids produce hydrogen ions, alkalis produce hydroxide ions

Question 17

What are bases, acids and alkalis?

Answer 17

Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions

Question 18

What is the pH scale and what does a ph of 7 show?

Answer 18

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

Question 19

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

Answer 19

H+ + OH- —> H2O

Question 20

What is a strong acid and weak acid?

Answer 20

Strong acid is completely ionised in aqueous solution; weak acid is only partially ionised in aqueous solution

Question 21

What happens to pH as concentration of H+ increases?

Answer 21

The pH decreases

Question 22

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

Answer 22

• Concentrated acid has more moles of acid per unit volume than 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 (strong) or only partially (weak)

Question 23

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

Answer 23

Increases by a factor of 10