Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Fatpants15 on January 23, 2017, 03:01:41 PM
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Here's the problem from my homework. The amount of iron and manganese in an alloy can be determined by precipitating the metals with 8-hydroxyquinoline, C9H7NO (FW 145.16). After weighing the mixed precipitate, the precipitate is dissolved and the amount of 8-hydroxyquinoline is determined by another method. In a typical analysis, a 0.1273 g sample of an alloy containing iron, manganese, and other metals was dissolved in acid and treated with appropriate masking agents to prevent interference from other metals. The iron and manganese were precipitated and isolated as Fe(C9H6NO)3 (FW 488.29) and Mn(C9H6NO)2 (FW 343.24), yielding a total mass of 0.8678 g. The amount of 8-hydroxyquinoline in the mixed precipitate was determined to be 5.276 mmol. Calculate the %(m/m) Fe and %(m/m) Mn in the alloy.
I'm not sure where to start because I was out of town due to family things. Any help is appreciated!
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You should show your attempt to receive help, that's part of the forum rules.
Hint: you can write one equation using number of moles and a second equation using masses. That's enough to solve the problem.
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Okay here's my work. I couldn't upload earlier and I didn't want to type it all out. Am I on the right track?
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Your second equation is close, but the RHS is wrong.
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What is the RHS? And how do I fix it?
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RHS means Right Hand Side of the equation.
And how do I fix it?
You look at it wondering "What could have gone wrong?" ;)
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Okay I think I got it now. Does this look good?
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Isn't it the same picture?
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Yeah it was supposed to post an updated one. Here's the updated one. I think I got it but I'm worried because my two percent masses add up to almost 100% but it said there were other metals present
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Your equations are OK but your math is wrong.
Beware: this system of equation can be quite sensitive to rounding errors.