| Chapter 2D Reading Guide |
What properties does
Cu have that makes it useful?
1)
2nd best conductor of electricity
2) it is fairly non-
reactive so it resists corrosion.
3) ductility - ability
to be drawn into a wire.
4) forms alloys with
other metals (ie. bronze and brass are alloys of copper)
Copper is mined as an ore.
What factors make it profitable to mine an ore?
1) supply and demand
2) type of mining and
processing required
3) amount of useful
ore at the sight
4) distance of mine
from processing facility
5) percent metal in
ore? (1st copper mines were rich in copper; 35 - 88% Copper. Todays mines
much lower;1 % Cu)
Copper Ores
Cu2S - chalcocyte
Cu2O - cuprite
Cu2CO3(OH)2 - malachite
Copper ores are "reduced" to copper metal which is used for:
We can calculate the percent Cu in the mineral chalcocyte, Cu2S.
% Cu in Chalcocyte = 2 Cu
x 100 = 2 x 63.5
x 100 = 79.9 % Cu
Cu2S
(2[63.5]+32)
Of course, ores are not pure, but contain lots of other stuff like rocks and dirt. For example, a mine might contain 5% chalcocyte by mass. In this case, we would calculate the percent copper in the sample by taking 5 % of 79.9 %, which would turn out to be 4 %. If we had a 150 g sample from this mine, the mass of copper in the sample would be 4 % of 150 g, or 6 g.
Metal Reactivity
The first metals known to humankind were the less reactive metals. Gold and silver are both fairly nonreactive and were the first metals used in coins. Copper isn't quite as nonreactive, but it is fairly easy to extract from ore. It has been in use for probably 10,000 years or more. Bronze, a copper and tim alloy has been around since approximately 3800 BC. Iron has only been in use since about 1000 BC. The more reactive metals were only discovered in the last 200 or so years.
Extracting Metal From An Ore
Metals found in ores are combined with other elements in a compound. We learned earlier that metals have a positive charge (oxidation state) when they are combined with another element. When we extract the metal from the ore, the bonds are broken, and the metal is restored to its elemental form, with no electrical charge.
Reduction is the conversion of a combined metal into a free or elemental metal. Because combined metals have a positive oxidation state and elemental metals have an oxidation state of zero, we say the metal is reduced. For example:
2 CuO ---> 2 Cu +O2
Cu^+2 + 2 e ----> Cu^0 (Reduction of +2 oxidation state to 0 oxidation state)
Oxidation is the reverse process of reduction. When a metal in its elemental state rusts, tarnishes or corrodes, it is forming a compound with another element.The oxidation state in the elemental metal is zero and becomes positive when it combines with another element.
4 Fe + 3 O2 ---> 2 Fe2O3
Fe^0 ---> Fe^+3 + 3 e (Iron goes from 0 to +3 oxidation state)
Methods Of Extracting Metals From Their Ores
1) Pyrometallurgy - use of intense heat along with a reducing agent like carbon. The reducing agent will supply electrons to the combined metal to reduce its oxidation number to zero. If the reducting agent loses its electrons, it is being oxidized.
ie. We used pyrometallurgy to reduce CuO to Cu with heat and propane gas.
2) Electrometallurgy - an ore is melted and electrical current is passed through the liquid. The electricity supplies the electrons to reduct the combined metal's oxidation number to zero.
ie. We did an experiment similar to this. We used a battery to supply electricity and electrons to reduce copper ions from copper chloride into copper.
3) Hydrometallurgy - an ore is dissolved in a water solution. Another more active metal will lose electrons which will allow the metal ion from the ore to be reduced to its elemental state.
ie. This is similar to
putting an iron nail into a copper chloride solution and producing metallic
copper in the nail.
| Chapter 2D Reading Guide |