In the fall of 1989 I taught Intro Chemistry at Dalhousie University. The November 15 mid-term test had six questions of equal value and the following was one of them. The students in 1989 had 12 minutes to answer this question. As before, the class is expected to agree to a final answer for the question and all students that participate will get the same mark. The deadline for participation is midnight, October 22. Show all calculations and follow the rules of significant figures.
A 5.810g sample of an iron ore was dissolved in 20.00 mL of concentrated HCl (12.3M) then diluted with water and titrated with permanganate solution (51.42 mL, 0.11678M). If the mineral in the ore was Iron(IV)sulphide what was its % mass in the ore?
5 Fe(2+) + MnO4(-) + 8 H(+) --> Mn(2+) + 4 H2O + 5 Fe(3+)
BONUS: If the total volume of solution after the reaction was 523 mL what was the HCl concentration after the reaction?
2 comments:
I agree with Kermit of the first part of the problem. As for the bonus I used the equation
Cf·Vf = Ci·Vi and the rearranged it to find the final concentration of HCl Cf = Ci·Vi/Vf
so, Cf = 12.3M·0.0200L/0.523L which equals the final concetration of 0.470M HCl.
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