How Do You Solve These Chemistry Stoichiometry Problems?

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Discussion Overview

The discussion revolves around solving stoichiometry problems in chemistry, specifically focusing on calculations involving moles and mass of elements such as carbon and manganese. Participants explore the accuracy of their calculations and the proper use of significant figures.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant calculates the number of moles of carbon in 315 mg of graphite but receives feedback that their molecular weight value is incorrect.
  • Another participant expresses uncertainty about how to find the number of manganese atoms in 1 kg of bone, indicating a need for clarification on the setup of the problem.
  • There is a discussion about the significance of using the correct molecular weight for carbon and the impact of significant figures on the final answer.
  • Participants discuss the clarity of mathematical expressions and the importance of presenting steps in a clear manner.
  • One participant questions whether they should convert their answer from grams to kilograms, indicating confusion about the original question.

Areas of Agreement / Disagreement

Participants generally agree on the need for accuracy in calculations and the importance of significant figures, but there is no consensus on the best approach to clarify the setup for the manganese problem or the correctness of the initial calculations.

Contextual Notes

There are unresolved issues regarding the proper use of significant figures and the clarity of mathematical statements in the calculations presented. Additionally, the relationship between the number of manganese atoms and the mass in kilograms remains unclear for some participants.

triplepie
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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.
 
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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
 
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.
 
triplepie said:
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?
 
triplepie said:
Oh, so I just convert my answer from grams to kilogram?

Why? What was the actual question?
 

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