# Chemistry stoichiometry problems

1. Graphite is a crystalline form of carbon used in "lead" pencils. How many moles of carbon are in 315mg of graphite?

2. 315mg = .315g

0.315 g C (1 mol C / !2 g C)

3. 0.026 mol C

2.1 Manganese is a transition element essential for the growth of bones. What is the mass in grams of 3.22 x 10^20 Mn atoms, the number found in 1 kg of bones?

2.2 3.22 x 10^20 Mn atom ( 1 mol Mn/ 6.022 x 10^23 atom Mn) = 5.35 x 10^-4 mol MN ( 54.94 g Mn/ 1 Mol Mn) = 293.77 x 10^-4 g Mn

2.3 293.77 x 10^-4 Mn

Im not sure how to find the number in 1 kg bone.

symbolipoint
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Your graphite result is wrong. The molecular weight of the Carbon element is 12.011. What did your "!2" value come from?

I ignored the .011 because i was just practicing.

but yeah, if i wanted it more accurate, I should have added .011

symbolipoint
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Triplepie,
You are misusing your mathematical statements in the manganese solution but you seem to have the right idea about your choice and direction of the conversion ratios. Note that you reported too many significant figures.

Even if the calculation for manganese is correct (ignoring the quantity of significant figures), you should lose much credit for the way you expressed the steps. Make clear and unmistakable mathematical statements as steps; do not shove steps together and misuse the equality relation symbol.

Ok, thanks, I'm not that good with sig figs and was going google on how to do it, can you tell me how to find 1kg in bone for the second problem, I don't know how to set it up.

symbolipoint
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Ok, thanks, I'm not that good with sig figs and was going google on how to do it, can you tell me how to find 1kg in bone for the second problem, I don't know how to set it up.

What? You just found the Mn in the 1 kg of bone. The only problem in your final result is the number of significant figures, as long as no other computational mistakes were made.

Oh, so I just convert my answer from grams to kilogram?

symbolipoint
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