1. Percent Composition Definition: the percent, by mass, of each material found in an item (coin) or amount substance such as ore

2. So the percentage of aluminum in the ore ranges from 20 to 25%. In the video about aluminum production, we learned that 4 to 5 tons of bauxite, a rock with several aluminum- bearing ores, is needed to produce 1 ton of aluminum metal. What is the percent of aluminum in the bauxite? The percent of aluminum can be found by dividing the mass of the aluminum by the total mass of the bauxite.

3. Composition of Materials In considering whether an ore is a useful source of a metal, the percent composition of the ore is a key factor. You have seen that separating a metal from its ore can be costly, both in terms of energy and money. Therefore it is desirable to identify ores with the highest percentage of metal for mining and processing.

4. How to Calculate Percent Mass Let’s use carbon dioxide as an example. First, we need to know the molar mass of CO 2 : 1 mol C x12.01g/mol + 2 mol O x16.00g/mol = 44.01 g/mol CO 2 Second, now find the percent of each constituent. Oxygen: Carbon: NOTE: The total percent should equal 100%

5. Copper Ores Chalcocite Cu 2 S Chalcopyrite CuFeS 2 Malachite Cu 2 CO 3 (OH) 2 Let’s find the percent copper by mass in chalcocite. Molar mass of Cu 2 S = 2 x 63.55g/mol + 32.07g/mol = 159.17 g

6. Now work these problems. 1.The chemical formula for azurite, another copper-containing mineral, is Cu 2 (CO 3 ) 2 (OH) 2. Complete an ION INVENTORY for azurite. 2.Calculate the percent copper in chalcopyrite CuFeS 2 3.Calculate the percent copper in malachite Cu 2 CO 3 (OH) 2

7. 4.We found that the percent copper in chalcocite is 79.85%. Compare this with your results for chalcopyrite and malachite above and decide which mineral could be mined most profitably. (Assume the ores have the same concentration and can be extracted at the same cost.)

8. Another consideration Remember, an ore can be made up of several different minerals, and not all of them may contain the metal you’re looking for. In deciding whether an ore can be mined profitably, we also need to consider the quantity of the target mineral actually contained in the ore. Would an ore that contains 20% chalcocite be more desirable than one with 45% chalcocite?

9. So TWO factors must be taken into account when deciding on the quality of a particular metal source: 1)The percent MINERAL in the ore; and 2)The percent METAL in the mineral Diagrams can be useful in understanding how these two factors relate to the total metal found in an ore ►

10. Consider an ore that contains 10% of a mineral. We represent this below by the larger grid, where 10 out of 100 boxes are shaded. The expanded view of one of the shaded boxes represents the METAL CONTENT of the mineral, here 85 out of 100 or 85%. MINERAL CONTENT OF AN ORE—10% or 10 out of 100. The total metal content of the ore is the metal content times the mineral content: 85% of 10% =.85 x 10% = 8.5%

11. Your turn to practice. 5.Suppose you have the choice either to mine ore that is 20% chalcocite (Cu 2 S) or ore that is 30% chalcopyrite (CuFeS 2 ). Assuming all other factors are equal, which would you choose? Draw diagrams similar to the one on the last slide to support your answer.