chemistry Flashcards
what is a base
substances that accept hydrogen ions H+
what is alumina
a form of aluminium oxide found in mineral bauxite, it is extracted and purified using the bayer process.
what are the stages of the process of extracting aluminium
- bauxite is mined
- molten alumina is electrolysed using the hall-heroult process
- cryolite is added to aluminia to lower melting point and save energy
- lining of tank is made from carbon which acts as the negative electrode to form molten aluminium: Al3+ +3e-=Al
- positive electrodes are made from carbon, oxide ions are oxidised to form oxygen gas: 202- = 02 +4e-
- the carbon electrodes have to be replaced regularly as they react with the oxygen as it forms.
what are the stages of the process of extracting titanium
- rutile is mined and it contains titanium dioxide
- it is extracted using the kroll process
- titanium dioxide, coke (form of carbon) and chlorine are heated together at 900c to form titanium chloride: TiO2(s) + 2C(s) +2Cl2(g) = TiCl4(g) + 2CO(g)
- magnesium is used as a reducing agent to form titanium: TiCl4(g) + 2Mg(l) = Ti(s) +2MgCl2(l)
- process is expensive due to large amounts of energy needed to create the very high temperatures involved.
- the process is time consuming as it is a batch process
what is NaCl
Brine
what does brine produce
chlorine, hydrogen and sodium hydroxide
what happens at the anode (positive electrode) during the electrolysis of brine
chloride ions react at the anode to form chlorine gas: 2Cl- (aq) = Cl2 (g) +2e-
each chloride ion has lost an electron so the reaction is oxidation
what happens at the cathode (negative electrode) during the electrolysis of brine
hydrogen ions from the water react at the cathode to form hydrogen gas: 2H+ (aq) +2e- = H2 (g)
each hydrogen ion has gained an electron so the reaction is reduction
the remaining sodium ions and hydroxide ions stay in solution forming sodium hydroxide solution, referred to as caustic soda
why do we use a diaphragm cell
- used in the chlor-alkali industry
- allows brine to pass from one side to the other side without chlorine and hydrogen gas from passing through, so the gaseous products are kept separate.
why do we use a membrane cell
- used in the chlor-alkali industry
- has an ion-exchange membrane dividing the cell
- allows the positive sodium ions, but will not allow negative chloride ions to pass through from the anode side to the cathode side.
- the brine enters the cell from the anode side and the sodium hydroxide is left over, the cathode is not contaminated by sodium chloride
what are the pros and cons of diaphragm cells
- cheaper to construct
- needs replacement regularly
- purity of sodium hydroxide is formed lower and the cell uses more energy per tonne of chlorine produced.
what are the pros and cons of membrane cells
- more expensive to construct
- membrane needs little maintenance
- purity of the sodium hydroxide formed is high and the cell uses slightly less energy per tonne of chlorine produced
what is the molecular formulae
tells you the number and type of each atom present in a molecule. eg, butaine, C4H10 contains 4 carbon atoms and 10 hydrogen atoms
what is the displayed formulae
these show all the bonds present in a molecule so its clear to see how each join to others.
what is a structural formulae
shows how all the atoms are arranged but doesnt require all bonds to be shown.
