Introduction
The metals industry has long used chemistry in isolating metals. Two of the common procedures used are roasting and smelting. The roasting process involves heating the ore to decompose unstable ions which are bonded to the metal. Three common examples are given below, where M represents a metal ion:
- MCO3(s) <---> MO(s) + CO2(g)
- MSO3(s) <---> MO(s) + SO2(g)
- MOH(s) <---> MO(s) + H2O(g)
In each case, the second product is gaseous and is simply expelled to the environment. The metal oxide (MO) is purified by heating with powdered charcoal. This is the key to smelting. A replacement reaction occurs as follows:
- MO(s) + C <---> CO2(g) + M(s)
Thus, the metal is released and can be isolated by any of several methods, including the flotation method used in this procedure.
CAUTION: Items used in this lab will be quite hot. Please be careful to prevent burns.
Procedure
Mount an iron ring on a ring stand, equip with a pipestem triangle and obtain a Bunsen burner, crucible and cover. Heat the empty crucible and cover for about one minute using the Bunsen burner. Allow to cool, then mass the crucible and cover. Be sure to record this mass.Click here to find out how to use a crucible correctly.
Add 2-3 grams of copper(II) carbonate to the crucible and remass. Place the crucible on the pipestem triangle and put the cover on, slightly tilted. Begin heating slowly , gradually increasing the temperature until there is evidence of a reaction. When the color change is complete, cool and remass. Heat for one more minute, cool, and remass. If there is more than .03 g difference between the masses after the second heating, then heat for another minute, cool, and remass.
While the contents are cooling measure out about 1 gram of charcoal. Add to the cooled contents of the crucible, mix together using a clean, dry stirring rod. Be sure to scrape off any solid that clings to the stirring rod.
Return the crucible to the pipestem triangle and begin heating again. When evidence of a chemical reaction appears, watch carefully. (You should hold the crucible cover with forceps to better observe the process. If particulate matter is emitted, cover quickly.) Heat strongly for 5 minutes more. Then turn off the burner, and using tongs, quickly pour the contents of the crucible into a 400 mL beaker containing 300 mL water.
Hold the beaker under a faucet and carefully run water into the beaker until the wash water is clean. Decant the water carefully, and pick out the pieces of metal. Place the metal on a massed piece of filter paper that is marked with your initials for later identification. Allow to air dry overnight and remass the metal and filter paper the next day.
Results and Discussion
Determine the % by mass of CO2 lost and the % yield of copper.Unless you have 100% of the expected yield of the copper, discuss where in your procedure you could have introduced error.
Applications Problems
1. What is the mass percent of metal in each of the following ores?
- Fe2O3, CaSO4.2H2O, Al2O3.2H2O, Zn2SiO4
2. Antimony metal can be obtained from Sb4O6 by reaction with carbon :
Sb4O6(s) + 6C(s) ---> 4Sb(s) + 6CO(g)
- a. If 2.50 x 102 g C and 3.00 x 102 g Sb4O6 are used, identify the limiting reactant.
- b. Assuming 100% yield, what mass of Sb is formed?
- c. If the yield was 82.0%, what mass of Sb4O6 would be required to react with excess carbon to form 1.00 kg of Sb?
3. A certain copper ore contains 6.1% Cu2S by mass. When the ore is concentrated by flotation, 20% of the Cu2S is lost. Of the Cu2S that remains, 15% is lost in the conversion to copper. How much ore is required to yield 1.00 kg of copper?
4. When copper(I) sulfide is roasted in air, the atmosphere is contaminated by SO2:
Cu2S(s) + O2(g) ---> 2Cu(s) + SO2(g)
This is eventually converted to sulfuric acid, which falls as acid rain. Suppose the sulfur dioxide formed from 1.00 g Cu2S spreads out over 2.0 x 103 m3 of air, where it is converted to sulfuric acid. How many H2SO4 molecules are there in 1.00 cm 3 of this air?