chemical changes

Question 1

What are the two definitions of oxidation?

Answer 1

Oxidation is the loss of electrons.

Oxidation is the gain of oxygen.

Question 2

What are the two definitions of reduction?

Answer 2

Reduction is the gain of electrons.

Reduction is the loss of oxygen.

Question 3

What is a redox reaction?

Answer 3

A redox reaction is when oxidation and reduction happen simultaneously.

Question 4

What is the reactivity series?

Answer 4

potassium
sodium
lithium
calcium 
magnesium
(carbon)
zinc
iron
(hydrogen)
copper

Question 5

What is the reactivity of metals related to?

Answer 5

The reactivity of metal is related to its tendency to form positive ions.

Question 6

How does the reactivity series react with water?

Answer 6

with water:

• potassium, sodium and lithium - very rapid
• calcium - quite rapid
• magnesium, zinc, iron and copper - no reaction

Question 7

How does the reactivity series react with dilute acid?

Answer 7

with dilute acid:

• potassium, sodium and lithium - dangerously fast
• calcium - extremely vigorous
• magnesium - rapid
• zinc - quite rapid
• iron - quite slow
• copper - no reaction

Question 8

What is the definition of an acid?

Answer 8

An acid will produce hydrogen ions (H+) in aqueous solutions.

Question 9

What ions are sulfuric acid made up of?

Answer 9

H2SO4 is made up of 2H+ and (SO4)2-.

Question 10

What are bases?

Answer 10

Bases are chemicals which can neutralise acids to produce salt and water. They are usually metal oxides or hydroxides.

Question 11

What is another name for bases that are soluble in water?

Answer 11

Bases that are soluble in water are called alkalis.

Question 12

What is the definition of an alkali?

Answer 12

Alkalis produce hydroxide ions (OH-) in aqueous solutions.

Question 13

Give the equation for neutralisation.

Answer 13

H+ + OH- –> H2O

Question 14

What is the pH for acids and alkalis?

Answer 14

acids - pH 1 - 6

alkalis - pH 8 - 14

Question 15

What are two ways to measure pH?

Answer 15

A pH probe or a universal indicator.

Question 16

What are the products from acid + metal?

Answer 16

acid + metal –> salt + hydrogen

Question 17

What kind of salts does hydrochloric acid produce?

Answer 17

Hydrochloric acid produces salts ending in chloride.

Question 18

What kind of salts does sulfuric acid produce?

Answer 18

Sulfuric acid produces salts ending in sulfate.

Question 19

What kind of salts does nitric acid produce?

Answer 19

Nitric acid produces salts ending in nitrate.

Question 20

What are the products from acid + alkali OR base?

Answer 20

acid + alkali OR base –> salt + water

Question 21

What are the products from acid + metal carbonate?

Answer 21

acid + metal carbonate –> salt + water + carbon dioxide

carbonate is (CO3)2-

Question 22

What is a strong acid? Give examples.

Answer 22

Strong acids fully ionise in aqueous solutions.

Examples are hydrochloric, nitric and sulfuric acid.

Question 23

What is a weak acid? Give examples.

Answer 23

Weak acids partially ionise in aqueous solutions.

Examples are carbonic acid, ethanolic acid and citric acid.

Question 24

What does each unit of the pH scale represent?

Answer 24

As the pH scale decreases by 1, the concentration of hydrogen ions increases by 10x.

Question 25

What happens during electrolysis?

Answer 25

During electrolysis, an electric current is passed through the melted or aqueous ionic compound (electrolyte), and the ions are attracted to an electrode (a solid that can conduct electricity, graphite or metal). + metal ions go to the cathode (negative) and gain electrons - non-metal ions go to the anode (positive) and lose electrons This creates a flow of charge.

Question 26

What is the order of discharge for electrolysis at the anode and cathode?

Answer 26

anode - Ag+ > Cu+ > H+ > other | cathode - Cl-, Br- > OH- > other

Question 27

Why do we not use metals less reactive than carbon in electrolysis?

Answer 27

As they can be extracted by reduction with carbon, which is much cheaper.

Question 28

Where is aluminium extracted from?

Answer 28

Aluminium is extracted from its ore, bauxite, Al2O3. Mixed with cryolite to lower melting point when extracted.

Question 29

What are the half equations at each electrode for the extraction of aluminium from Al2O3?

Answer 29

anode - 202- --> O2 + 4e- | cathode - Al3+ + 3e- --> Al

Question 30

Why must the anode be replaced regularly?

Answer 30

The anode must be replaced regularly as O2 reacts with carbon on the electrode to form CO2.

Question 31

In aqueous solutions, how do the water molecules ionise at each electrode?

Answer 31

anode - 4OH- --> O2 + 2H2O + 4e- | cathode - 2H+ + 2e- --> H2