Factor/label conversion techniques and sig figs. Chemistry.

Question

Egargite is an intrusive igneous copper arsenic sulfide mineral  (Cu3AsS4) which is an important ore of copper in copper sulfide deposits. The mineral consists of approximately 48.407% Cu by mass. (The curious chemistry student can verify that estimate using molar masses of the elements from the periodic table and the calculated molar mass of the compound from the chemical formula.) How many pre-1982 pennies with an average mass of 3.11g/penny, and copper composition of approximately 95.0% Cu  (and 5%Zn) could be manufactured from one 13.500 metric ton truck of enargite copper sulfide ore if the ore is only 34.500% enargite by mass (assuming the enargite is the only copper bearing mineral present and there is 100% success in the copper extraction process.)

Answer 1

The steps to solve this question are:

 

1. Cu per penny = 3.11g x95% =3.11g x 0.95 = 2.95g/penny

 

2. 13.5 metric tons of ore x 34.5% = 4.6575 metric tons of Cu₃AsS₄

 

3. 4.6575 metric tons x % of Cu in compound = 4.6575 x 0.48407 = 2.25 metric tons of Cu

 

4. 2.25 metric tons x 1000kg/ton = 2254.7kg

 

5. 1000g/kg x 2254.7kg = 2,254,695.7g

 

6. 2,254,695.7g ÷ 2.95g/penny = 764,303 pennies