Electolysis Flashcards
State uses of Alumina
fillers , paint,
What is the chemical name of Alumina
Aluminium oxide - Al2O3
What is the name of the ore where Alumina is found?
Bauxite
What is the equation for the reaction of Al2O3 and HCl? What are the conditions
Al2O3 (s) + 6HCl (aq) → 2AlCl3 (aq) + 3H2O (l)
Warm conditions
What is the equation for the reaction of Al2O3 and NaOH? What is the name of the product?
Al2O3 (s) + 2NaOH + 3H2O (l) → 2NaAl(OH)4
Sodium tetra-hydroxo-aluminate
What are the stages of the Bayer process?
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)
What is the Al2O3 (s) produced from the Bayer process used for?
Used in the Hall-Heroult process to form aluminium by electrolysis.
What is added to the aluminium oxide in the Hall-Heroult process? Why?
Cryolite is added to lower the melting point and save energy.
What are the electrodes made of in the Hall-Heroult process?
Positive electrode = carbon
Negative electrode in the tank = carbon
Where is aluminium produced? What is the half equation?
At the negative electrode REDUCTION
Al3+ + 3e- → Al
Where is the oxygen produced? What is the half equation?
At the positive electrode OXIDATION
2O2- → O2 + 4e-
Why must the carbon electrodes be replaced regularly?
They react with the oxygen produced to form carbon dioxide.
What is brine?
NaCl(aq) solution
What are the products of the electrolysis of brine?
Chlorine - Cl2 - at the positive electrode Hydrogen - H2 - at the negative electrode Sodium hydroxide - NaOH - remaining in the solution
What is the reaction at the positive electrode?
2Cl- (aq) → Cl2 (g) + 2e-
OXIDATION
What is the reaction at the negative electrode?
2H+ (aq) + 2e- → H2 (g)
REDUCTION
OIL RIG?
Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons)
What are the pros and cons of the diaphragm cell?
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
What are the pros and cons of the membrane cell?
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
What is the name of the ore Titanium is found in? What does it contain?
Rutile
Contains TiO2 - titanium (IV) dioxide
What is the Kroll process?
Method of extracting titanium from titanium dioxide.
What are the stages of the Kroll process?
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)
What are the cons of the Kroll process?
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).
What is a “batch process”?
A process where the reactor has to be shut down and cooled before the product (titanium) can be removed for purification.
