4-Chemical Changes

Question 1

What is an acid?

Answer 1

A substance that forms an aqueous solution with a pH less than 7 and forms H+ ions in water.

Question 2

What is an alkali?

Answer 2

A base that dissolves in water with a pH greater than 7. Forms OH- ions in water.

Question 3

What is a base?

Answer 3

Substance with a pH greater than 7

Question 4

What would be considered a strong acid?

Answer 4

pH 1-3, completely ionised in aqueous solution.

Question 5

Give three examples of strong acids.

Answer 5

Examples of strong acids are hydrochloric, nitric and sulfuric acids.

Question 6

What is a weak acid?

Answer 6

pH 3-6, only partially ionised in aqueous solution

Question 7

Give three examples of weak acids.

Answer 7

Examples of weak acids are ethanoic, citric and carbonic acids.

Question 8

What is the reaction between acids and bases?

Answer 8

Neutralisation - acid + base -> salt + water

Question 9

What is the neutralisation reaction in terms of H ions?

Answer 9

Hydrogen ions rect with hydroxide ions to produce water,
H+ + OH- ->H20

Question 10

Examples of pH1 acids?

Answer 10

Car battery acid, stomach acid

Question 11

Examples of pH3 acids?

Answer 11

Vinegar, lemon juice

Question 12

Examples of pH4 acids?

Answer 12

Acid rain

Question 13

What happens to the rate of reaction when theres a higher concentration of H+ ions?

Answer 13

If concentration of H+ ions is higher, rate of reaction will be faster, so strong acids will be more reactive than weak acids.

Question 14

How is concentration of pH measured and tested?

Answer 14

Concentration of H+ ions in a solution, tested by universal indicator or a pH probe.

Question 15

When pH decreases by a factor of 1, what does H+ ions increase by?

Answer 15

10

Question 16

What is the rule for changing pH and concentration of H+ ions?

Answer 16

Factor of H+ ion concentration changes by 10^-x
(x is the difference of pH)

Question 17

What is the reaction of metal oxides and metal hydroxides with acids?

Answer 17

All metal oxides and metal hydroxides react with acids to form a salt and water.
Acid + metal oxide -> salt + water
Acid + metal hydroxide -> salt + water

Question 18

Reaction of acids with metals?

Answer 18

Acids react with some metals to produce salt and hydrogen.

Question 19

Whats the reaction of acids and metal carbonates?

Answer 19

Acids and metal carbonates react to produce salts, water and carbon dioxide.

Question 20

What does the salt produced depend on?

Answer 20

The salt produced depends on the acid used and the positive ions in the base, alkali or carbonate.

Question 21

How can soluble salts be made?

Answer 21

•Reacting acids with solid, insoluble bases
•eg. metals, metal oxides, hydroxides, carbonates.

Question 22

What is the reactivity series?

Answer 22

How well a metal reacts, their reactivity towards other substances.

Question 23

How is the reactivity of a metal determined?

Answer 23

How easily they lose electrons to form positive ions.

Question 24

What is the order of elements in the reactivity series?

Answer 24

Potassium-K
Sodium-Na
Lithim-Li
Calcium-Ca
Magnesium-Mg
Carbon-C
Zinc-Zn
Iron-Fe
Hydrogen-H
Copper-Cu

Question 25

How would a very reactive metal e.g Potassium, sodium, lithium, calcium react with a dilute acid?

Answer 25

Vigorously and explosively, moving quickly, lots of bubbles/fizzing and hydrogen given off.

Question 26

How would a fairly reactive metal e.g magnesium react with a dilute acid?

Answer 26

Vigorously, loads of bubbles produced

Question 27

How would a not very reactive metal e.g zinc or iron react with a dilute acid?

Answer 27

React slowly with a cold acid but more strongly if you heat them up.

Question 28

What is oxidisation?

Answer 28

Metals reacting with oxygen to produce metal oxides - gain oxygen. Electrons are lost.

Question 29

What is reduction?

Answer 29

Loss/ removal of oxygen. Electrons are gained.

Question 30

How can metals be extracted from their oxides/

Answer 30

Metals less reactive than carbon can be extracted from their oxides by reduction with carbon. Metals more reactive extracted with electrolysis.

Question 31

What does electrolysis mean?

Answer 31

Splitting up with electricity

Question 32

How does electrolysis work?

Answer 32

*Ionic compounds melted or dissolved are free to move around and conduct electricity
*Electric current passed through electrolytes causing ions to move to electrodes
*Positive move to negative cathode
*Negative move to positive anode
*Ions discarded at electrodes to produce elements

Question 33

What happens when a simple ionic compound is electrolysed in a molten state?

Answer 33

*Metal is produced at the cathode
*Non-metal produced at the anode

Question 34

What are the disadvantages of using electrolysis to extract metals?

Answer 34

*Large amounts of energy used
*Positive carbon anode needs to be continuously replaced

Question 35

What can be produced at the negative cathode and under what conditions?

Answer 35

Hydrogen produced if metal more reactive than Hydrogen.

Question 36

What can be produced at the positive anode and under what conditions?

Answer 36

Oxygen unless solution contains halide ions when halogen produced

Question 37

What are the uses of aluminium and its alloys?

Answer 37

•Pans
•overhead power cables
•cooking foil
•drink cans
•bicycle frames and car bodies

Question 38

What is the equation for the electrolysis of aluminium oxide?

Answer 38

Aluminium oxide –> aluminium + oxygen

Question 39

What is the half equation at the cathode?

Answer 39

Al3+ + 3e- –> Al

Question 40

What is the half equation at the anode for extraction of aluminium?

Answer 40

2O^2- –> O2 + 4e

Question 41

How is aluminium extracted from aluminium oxide?

Answer 41

•electrolysis of aluminium oxide mixed with molten cryolite
•to lower melting point and reduce energy needed
•aluminium formed at negative cathode
•oxygen produced at positive anode