extracting a purifying metals.
Most metals are found as compounds in the Earth's crust. The metal ores are mined and the metals will then be extracted by reduction. however the method depends on how reactive the metal is;
- if the metal is very reactive then the metal will be extracted by electrolysis
- if the metals are not very reactive then they will be extracted by reduction with carbon or carbon monoxide
- unreactive metals can be found naturally in the Earth's crust.
- Barrier protection-prevents oxygen and/or water coming into contact with iron/steel e.g. painting, oiling or using a polymer coating.
- Galavanising- this is covering steel in a layer of protective zinc that oxidises.
- Sacrificial protection- this involves attaching blocks of more reactive metals to big structures made of iron e.g. ships; an electrochemical cell is formed and the reactive metal corrodes preferentially.
D block elements: transition metals.
A transtion metal is defined as a D block element that forms at least on ion with a partially filled sub-shell of D electrons.
properties of transition metals.
They are good conductors of heat and electricity, they are dense and have higher melting and boiling points. They are hard and durable. This makes them useful in a range of ways e.g. alloys.
All have variable oxidation states, form coloured ions, form complexes and have catalytic activity.
Many catalyts are made from transition metals or their compounds. They can act as homogenous or heterogenous catalyts.
In a complex, a central metal atom or ion is surrounded by ligands(molecules or anions with one or more lone pairs of electrons)
Ligands form dative covalent bonds with the central metal atom or ion. The number of bonds between the ligand and the central metal is called the coordiantion number. Ligands can form one bond to the central metal(monodentate), two bonds(bidentate) or many bonds (polydentate)
coordination number of 6- octahedral. coordination number of 4- tetrahedral or square planar. coordination number of 2- linear.
- Write the number of each type of ligand
- Write the name of each ligand in alphabetical order.
- Write the name of central metal- if overall positive then english name if overall charge is negative then name ends in -ate
- Write oxidation number of metal in brackets.
Redox reaction can be thought of as two different reactions occuring simultaneously; a reduction rection and a oxidation reaction.
Combining half equations.
First write down the two half equations, then decide which is the oxidation reation and reverse it. Then balance the equation so there are the same amount of electrons on both sides, add the equations together and cancel down.
Electrode potential is the tendency for a metal to release electrons. The more negative the electrode potential, the more likely it is to release electrons.
Where does colour come from?
If visible light falls on a coloured object, some wavelengths are absorbed and the rest are refletcted or transmitted; we see the reflected/transmitted wavelengths.
This is an experimental technique used to find the concentration of a coloured solution; the amount of light absorbed by a solution is proportional to the concentration of the solution.