Electolysis

Question 1

State uses of Alumina

Answer 1

fillers , paint,

Question 2

What is the chemical name of Alumina

Answer 2

Aluminium oxide - Al2O3

Question 3

What is the name of the ore where Alumina is found?

Answer 3

Bauxite

Question 4

What is the equation for the reaction of Al2O3 and HCl? What are the conditions

Answer 4

Al2O3 (s) + 6HCl (aq) → 2AlCl3 (aq) + 3H2O (l)

Warm conditions

Question 5

What is the equation for the reaction of Al2O3 and NaOH? What is the name of the product?

Answer 5

Al2O3 (s) + 2NaOH + 3H2O (l) → 2NaAl(OH)4

Sodium tetra-hydroxo-aluminate

Question 6

What are the stages of the Bayer process?

Answer 6

1) Crush the bauxite
2) React with NaOH(aq) at 17O oC to
form NaAl(OH)4 (aq)
3) Filter out solid impurities
4) Allow to crystallise to form Al(OH)3 5) Heat in rotary kiln to form Al2O3 (s)

Question 7

What is the Al2O3 (s) produced from the Bayer process used for?

Answer 7

Used in the Hall-Heroult process to form aluminium by electrolysis.

Question 8

What is added to the aluminium oxide in the Hall-Heroult process? Why?

Answer 8

Cryolite is added to lower the melting point and save energy.

Question 9

What are the electrodes made of in the Hall-Heroult process?

Answer 9

Positive electrode = carbon

Negative electrode in the tank = carbon

Question 10

Where is aluminium produced? What is the half equation?

Answer 10

At the negative electrode REDUCTION

Al3+ + 3e- → Al

Question 11

Where is the oxygen produced? What is the half equation?

Answer 11

At the positive electrode OXIDATION

2O2- → O2 + 4e-

Question 12

Why must the carbon electrodes be replaced regularly?

Answer 12

They react with the oxygen produced to form carbon dioxide.

Question 13

What is brine?

Answer 13

NaCl(aq) solution

Question 14

What are the products of the electrolysis of brine?

Answer 14

Chlorine - Cl2 - at the positive electrode Hydrogen - H2 - at the negative electrode Sodium hydroxide - NaOH - remaining in the solution

Question 15

What is the reaction at the positive electrode?

Answer 15

2Cl- (aq) → Cl2 (g) + 2e-

OXIDATION

Question 16

What is the reaction at the negative electrode?

Answer 16

2H+ (aq) + 2e- → H2 (g)

REDUCTION

Question 17

OIL RIG?

Answer 17

Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons)

Question 18

What are the pros and cons of the diaphragm cell?

Answer 18

Pros: cheaper to construct
Cons: the diaphragm needs replacing regularly, purity of the sodium hydroxide formed is low and the cell uses more energy per tonne of chlorine produced

Question 19

What are the pros and cons of the membrane cell?

Answer 19

Pros: needs little maintenance, purity of the sodium hydroxide formed is high and the cell uses less energy per tonne of chlorine produced
Cons: cheaper to construct

Question 20

What is the name of the ore Titanium is found in? What does it contain?

Answer 20

Rutile

Contains TiO2 - titanium (IV) dioxide

Question 21

What is the Kroll process?

Answer 21

Method of extracting titanium from titanium dioxide.

Question 22

What are the stages of the Kroll process?

Answer 22

Titanium (IV) dioxide, coke (carbon) and chlorine are heated together at about 900 to form titanium chloride.

  TiO2 (s) +2C(s) +2Cl2 (g) →TiCl4(g) +2CO(g) 2) Magnesium is used as a reducing agent to form titanium. TiCl4 (g) + 2Mg (l) → 2Mg (s) + 2MgCl2 (l)

Question 23

What are the cons of the Kroll process?

Answer 23

Cons:

• It is expensive - due to large amount of energy being needed
• Magnesium in step 2 is made from electrolysis which requires high energy.
• The process is time consuming (batch process).

Question 24

What is a “batch process”?

Answer 24

A process where the reactor has to be shut down and cooled before the product (titanium) can be removed for purification.

Question 25

What are some properties of titanium?

Answer 25

About 1.6x stronger than aluminium - Denser

- 2x a sti

Question 26

What are some properties of titanium?

Answer 26

Durable
- Strong ( but not as strong as
titanium)
- Rigid, unlikely to flex while in use - Cheaper than titanium
- Light
- Corrosion resistant