Electrolysis

Question 1

Define electrolysis

Answer 1

• The decomposition of ionic compounds into simpler substances using electricity
• ions must be free for electrolysis to work

Question 2

Explain the process of electrolysis of MOLTEN sodium chloride

Answer 2

• when sodium chloride (NaCl) is electrolyses it forms sodium ions (Na+) and chloride ions (Cl-)
• two electrodes are placed in molten sodium chloride with battery attached causing a current to flow and electrons move from cathode to anode
• Cl - ions move to anode where it is oxidised as it loses electrons to form chlorine gas 2Cl- = Cl2 + 2e-
• Na+ ions move to cathode where it is reduced as electrons are gained to forms sodium Na+. + e- = Na
• electrolysis carried out in diaphragm cell

Question 3

Describe the process of AQEOUS sodium chloride solution (brine)

Answer 3

• when sodium chloride is added to water it forms sodium ions, chloride ions, hydrogen ions and hydroxide ions. NaCl + H2O = Na+. + Cl-. + H+. + OH-
• Cl- move to anode where it is oxidised as it loses electrons to form chlorine gas. 2Cl- = Cl2 + 2e-
• H+ move to cathode where it is reduced as it gains electrons to produce hydrogen gas. 2H+. + 2e- = H2
• Na + are not as reactive as H+ so they dont gain electrons, it reacts with the hydroxide ions instead to form sodium hydroxide. Na+. + OH- = NaOH

Question 4

What are the similarities and differences of electrolysis of MOLTEN NaCl vs AQUEOUS Nacl

Answer 4

Similarities =
- Cl2 produced at anode

Differences =
- Na produced at cathode for molten
- H2 produced at cathode for aqueous
- NaOH is also produced from aqueous (sodium ions react with hydroxide ions)

Question 5

Describe how the electrolysis cells for brine (aqueous sodium chloride) is designed to keep all products seperate

Answer 5

• using a membrane cell = made of polymer, only allows positive ions to pass thru so only Na+ from sodium chloride solution can pass thru
• diaphragm in middle of cell is porous so solution can move thru from anode to cathode side
• there is always a higher level of liquid on anode side (left) to ensure liquid always flows from left to right
• to prevent any of the sodium hydroxide solution formed from moving back to where chlorine is being produced

Question 6

What are the advantages of using a membrane cell?

Answer 6

• sodium hydroxide solution being formed in the right never gets contained with any chloride ions
• keeps them seperated
• if they mix it will make bleach - not desired product
• if hydrogen and chlorine mix, they can explode due to exposure to heat or light

Question 7

Describe the process of extraction of titanium

Answer 7

• titanium is extracted from its ore - TiO2
• it is first converted into titanium (IV) chloride - TiCl4
• to convert TiO2 into TiCl4, it is heated with chlorine and carbon at a temp of 1000c. TiO2 + 2Cl2 + 2C = TiCl4 + 2CO
• then reduced to titanium by magnesium
• to reduce TiCl4, the vapour is reacted with molten mg in an argon atmosphere (in vessel) and temp is inc to 1000c. TiCl4 + 2Mg = Ti + 2MgCl2
• reaction takes place in argon atmosphere as oxygen or nitrogen from air, make metal in titanium brittle

Question 8

What are the properties of titanium?

Answer 8

• transition metal
• main ores are rutile - TiO2 and ilmenite - FeTiO3
• silvery metallic
• not magnetic
• mp is very high
• low density + lightweight
• resistant to corrosion
• strong

Question 9

Summarise how titanium is extracted from its ore

Answer 9

• titanium is extracted from its ore - TiO2
• it is first converted into titanium (IV) chloride - TiCl4 , then reduced to titanium by magnesium