Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: JesseTCarter on September 29, 2019, 10:30:22 AM
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Calculate salt (100 mg/kg salt and 39 mg/kg salt). Find the moles of iron for the high and low values of iron present in Himalayan pink salt. Use correct Sig Figs and include units.
I’m confused as to where I should start. I know salt is NaCl and I can get it’s MM but I’m not sure about Himalayan pink salt. Or where I would start to calculate the moles of iron, because wouldn’t there be other moles of Cl in the 100mg/kg and 39mg/kg of salt? Maybe I’m just overcomplicating it.
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The 100 mg/kg is the amount of Iron in NaCl. You should calculate the moles of it. The unit mg/kg can be expressed differently.
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So then would it be for 100mg/kg
584.4277 mol of iron mg/kg?
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Wait sorry that was for NaCl not Fe.
I got 55845 mol of iron mg/kg
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Stop fooling around - 100 mg is less than 0.002 mole.
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Sorry, I’m not trying to fool around. I’m just confused, my Lab and Lecture are on two different parts. I know that the molar mass of Fe is 55.845g/mol that’s 55845mg and what’s that divided by 100mg/kg of iron? That’s how I got my answer. I didn’t think it was right because I know moles would be an extremely smaller number. Avogadro’s number. 6.022e23. We just haven’t learned this yet, so I’m a little confused and lost. I’m used to converting a mol of something into grams or the other way around. When balancing equations and doing stoichiometry.
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Why not divide the opposite (100/55845)?
https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Map%3A_Chemistry_for_Changing_Times_(Hill_and_McCreary)/5%3A_Chemical_Accounting/5.4%3A_Molar_Mass%3A_Mole-to-Mass_and_Mass-to-Mole_Conversions
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100mg/55845mg makes so much more sense. I have no idea how I could miss that. 0.00179067061mg/kg mol of iron. That looks so much better.
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Now the second number and significant digits.
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0.000698361536mg/kg mol of iron
and
0.00179067061mg/kg mol of iron
With Sig Figs and rounding wouldn’t it just be
0.0007mg/kg mol of iron
And
0.002mg/kg mol of iron
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You did calculation only in nominator.
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Do you mean by that, that it’s only mg? And not mg per kg
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Or wouldn’t it just be moles?
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Now mol/kg but you did not use kg in calculations.
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That’s true, yes I only did mg because it’s mg of “something” per kg. We got it down to moles coming from mg; so we now have mol of “something” per kg. Would we leave it at mol/kg or does it boil down even further? The answers would have to be
0.0018mol/kg and 0.0007mol/kg
Because we’re calculating moles of iron from 100mg of iron per 1kg of salt and 39mg of iron per 1kg of salt. (It’s 1kg of salt, stated from a previous question in the pre-lab. I’m still unsure, but it sounds correct?)
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Numbers can be represented in several ways: normal number, number in scientific notation, an aliquot of the SI system. It may depend on the instructor's requirements. But significant numbers are important.
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Yeah, I need to work on my understanding of sig figs.
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Sig figs are not correct.
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I kind of figured they weren’t.
Would it look like
1.79e-3 mol/kg
and
7.0e-4 mol/kg
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I accept.
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Yay! Thank you so much for the help, and hints. I just needed that little push.