C4

Question 1

What are acids?

Answer 1

Substances that form hydrogen ions (H+) when they dissolve in water

Question 2

What are alkalis?

Answer 2

Bases that form hydroxide ions (OH-) when they dissolve in water

Question 3

What is the pH?

Answer 3

the measure of the concentration of H+ ions in a solution

Question 4

How can we measure pH?

Answer 4

• using an indicator (e.g. universal indicator)
• pH probe- always used to electronically measure the pH

Question 5

Describe the relationship between pH and concentration

Answer 5

As the concentration gets higher the pH gets lower.

• each decrease of 1 on the pH scale = concentration x 10
  eg. pH 3= 0.001, pH 4= 0.0001

Question 6

Describe a reaction between an acid and alkali(in terms of their ions)

Answer 6

a neutralisation reactions=
H+ + OH- → H20

Question 7

What is the word equation for neutralisation reactions?

Answer 7

acid + alkali → salt + water

Question 8

Give examples of common acids

Answer 8

• HCl = hydrochloric acid
• H₂S0₄= sulphuric acid
• HNO₃ = nitric acid

Question 9

Describe the reaction between an acid and a metal

Answer 9

acid + metal → salt + hydrogen

Question 10

Describe the reaction between an acid and metal oxide

Answer 10

acid + metal oxide → salt + water

Question 11

Describe the reaction between an acid and a metal hydroxide

Answer 11

acid + metal hydroxide → salt + water

Question 12

Describe the reaction between an acid and a metal carbonate

Answer 12

acid + metal carbonate → salt + water + carbon dioxide

Question 13

Describe how to make a soluble salt
(Required practical)

Answer 13

1. add dilute acid to a beaker
2. gently heat it(Bunsen burner) and add the insoluble base gradually
3. At first it will keep disappearing as it reacts but once the base stops disappearing it is in excess.
4. Filter out the excess base using filter paper and a funnel
5. With the salt solution, heat it in a water bath until around half of the water has evaporated
6. Stop heating it and allow the rest of the solution to cool
7. Filter the crystals out and then dry the crystals

Question 14

Describe how to carry out a titration to find the volume of sodium hydroxide that reacts with 25.0cm3 of hydrochloric acid

Answer 14

1. First, use a pipette to measure 25cm3 of hydrochloric acid and put it into the conical flask
2. Add the indicator e.g. phenolphthalein , methyl orange and place the white tile underneath
3. Fill the burette up until the 0 mark with sodium hydroxide and record the start volume of NaOH in the burette
4. Gradually add sodium hydroxide to the conical beaker using the tap on the burette and swirl
5. Once there is a permanent colour change, stop adding sodium hydroxide
6. record the final volume of the sodium hydroxide in the burette and do final volume - initial volume to calculate the volume that was added
7. Repeat the experiment, discount any anomalies and calculate a mean volume to improve the reliability of the results

Question 15

What is the reactivity series?

Answer 15

Potassium
Sodium
Calcium
Magnesium
Carbon
Zinc
Iron
tin
lead
Hydrogen
Copper
Silver
Gold

Question 16

Describe the reactions of the following metals with water
a)potassium
b)sodium
c)lithium

Answer 16

potassium ~ ignites instantly (sparks a lilac flame), the metal melts and floats, the metal moves very quickly on the surface of the water

sodium ~ sparks orange flame, travels speedily across the surface of the water, bubbles vigorously

lithium ~ turns pink in colour, bubbles and moves across the surface of the water

Question 17

What does the reaction between a metal and water produce?

Answer 17

metal hydroxide + hydrogen

Question 18

Describe the reactions of the following with acid
a) calcium
b)magnesium
c)zinc
d)iron
e)copper

Answer 18

• calcium has a violent reaction with rapid bubbling, hydrogen produced

• magnesium has bubbling, hydrogen produced

• zinc has slow bubbling, hydrogen produced

• iron has very slow bubbling

• copper has no reaction

Question 19

What is a reduction reaction?

Answer 19

A reaction where oxygen is lost

A reaction where electrons are gained

Question 20

What is an oxidation reaction?

Answer 20

A reaction where oxygen is gained

A reaction where electrons are lost

Question 21

What does OIL RIG stand for?

Answer 21

Oxidation
Is
Loss(of electrons)

Reduction
Is
Gain(of electrons)

Question 22

How are most metals found in the Earth?

Answer 22

As compounds- metal oxides

Question 23

Why aren’t metals such as gold found as metal oxides?

Answer 23

They are very unreactive

Question 24

How can metals less reactive than carbon be extracted?

Answer 24

a reduction reaction with carbon

Question 25

Why is carbon used?

Answer 25

It’s cheap and abundant

Question 26

What is used to extract metals that are more reactive than carbon?

Answer 26

Electrolysis

Question 27

What is a redox reaction?

Answer 27

A reaction where reduction and oxidation occurs at the same time

Question 28

What is a displacement reaction?

Answer 28

When a more reactive metal displaces (takes the place of) a less reactive metal = a redox reaction

Question 29

How do you write an ionic equation for Ca + FeSO4 → CaSO4 + Fe ?

Answer 29

- only show the particles that react and the products they form - SO4^2- are spectator ions - Ca + Fe² + → Ca² + Fe

Question 30

What is electrolysis?

Answer 30

the breakdown of an ionic substance using electricity

Question 31

What state must ionic compounds be in for electrolysis to be carried out?

Answer 31

molten or dissolved so electricity can be carried through

Question 32

What is an electrolyte?

Answer 32

the liquid required to conduct electricity= molten or dissolved ionic substance

Question 33

What is the name of the positive electrode and what does it attract?

Answer 33

Anode: attracts anions

Question 34

What is the name of the negative electrode and what does it attract?

Answer 34

Cathode: attracts cations

Question 35

During the electrolysis of molten ionic compounds, what happens at the cathode?

Answer 35

- the positively charged metal ion is attracted to the cathode - the ion is then reduced- gains electrons to become an atom - a thin layer of the metal is produced at the cathode

Question 36

During the electrolysis of molten ionic compounds, what happens at the anode?

Answer 36

- negatively charged non-metal ions are attracted to the anode - they are oxidised - lose electrons to become an atom - typically a gas is produced e.g. chlorine- pair up because they are diatomic and bubbles of Cl2 are produced

Question 37

Why would electrolysis be used?

Answer 37

When a metal is more reactive than carbon so it cannot be extracted by reaction with carbon

Question 38

What are disadvantages of electrolysis?

Answer 38

- very expensive - requires high amounts of energy

Question 39

What ions are present in an aqueous solution of an ionic compound?

Answer 39

H+, OH-, metal +, non-metal -

Question 40

What ion goes to the anode during the electrolysis of an aqueous solution?

Answer 40

- if a halide ion is present (group 7 ions), the halide ions go to the anode and halogen molecules are formed(diatomic and gas) - if no halide ions are present, the OH- ions go to the anode and are discharged to form oxygen and water (4OH- → 2H2O + O2 + 4e-)

Question 41

What ion goes to the cathode during the electrolysis of an aqueous solution?

Answer 41

- the least reactive element - if metal is more reactive than hydrogen, H+ ions go to the cathode and are discharged to form hydrogen gas (2H+ + 2e- → H2) - If less reactive, the metal ions go to the cathode and are discharged to form metal atoms(solid layer of metal)