Mole Homework Help: Iron & Water Mass Calculation

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Discussion Overview

The discussion revolves around a homework problem involving the calculation of the relative molecular mass of haemoglobin and the mass of a water molecule. Participants explore the implications of given percentages and atomic masses, as well as the calculations involved in determining molecular weights.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates the relative molecular mass of haemoglobin as 338.18 g/mol based on the mass of iron and its percentage in haemoglobin, but questions the answer provided in the answer sheet, which is 33818 g/mol.
  • Another participant suggests that the percentage of iron might be misprinted and proposes it could be 0.33% instead of 33%.
  • Participants discuss the number of molecules in a mole, with one stating that 1 mol of water contains 6.02 x 1023 molecules.
  • One participant attempts to calculate the mass of a water molecule using the formula 18/(6.02 x 1023) and arrives at 2.99 x 10-23 g, seeking confirmation of their calculation.
  • Another participant agrees with the calculation of the mass of a water molecule but expresses confusion over other numbers and symbols presented in the discussion.
  • A later post reiterates the calculation for the mass of a water molecule, confirming it as 2.99 x 10-23 g.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the percentage of iron in haemoglobin and whether it was misprinted. There is no consensus on the correct interpretation of the data or the calculations involved, as multiple viewpoints and calculations are presented.

Contextual Notes

Some calculations depend on the assumption of the percentage of iron in haemoglobin, which is contested. There are also unresolved aspects regarding the interpretation of the problem statement and the provided answer sheet.

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Homework Statement



1) Haemoglobin contains 33% by mass of iron. Each molecules of haemoglobin has two iron atoms. Calculate the relative molecular mass of haemoglobin.

2) The relative molecular mass of water is 18.0. Calculate the mass of water molecule.

Homework Equations



Relative atomic mass of iron = 55.8, hydrogen=1, oxygen =16

The Attempt at a Solution



1) 1 mol of haemoglobin contains 2 mol of iron atoms, hence mass of iron in haemoglobin = 55.8*2= 111.6g. Iron occupies the mass of haemoglobin by 33%, so the mass of a haemoglobin = (111.6*100)/33 = 338.18g. => Relative molecular mass of a haemoglobin = 338.18 g/mol.

BUT the answer give by the answer sheet is 33818 g/mol. Can anyone correct my solution?

2) I have no idea on this. Can anyone explain to me how to get the answer? The correct answer is 2.99*10^-23 g.

Thank you for your help.
 
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Are you sure it wasn't .33%? Your calculation looks OK, data looks off.

How many molecules of water in 1 mole?
 


Borek said:
Are you sure it wasn't .33%? Your calculation looks OK, data looks off.

How many molecules of water in 1 mole?

I guess its 0.33%, they might have misprinted it...

1 mol of water = 6.02 x 1023 molecules
hence mass/18 = 6.02 x 1023 => mass = 18*6.02*1023= 1.08*1025. Please correct me...
 
Last edited:


Nope.

If a dozen marbles weight 12g, what is a mass of one marble?

If a 6.02x1023 molecules weight 18g, what is a mass of one molecule?
 


Borek said:
Nope.

If a dozen marbles weight 12g, what is a mass of one marble?

If a 6.02x1023 molecules weight 18g, what is a mass of one molecule?

Mr of 1 molecule of water = 18/(6.02*1023)=2.99*10-23, therefore mass/2.99*10-23 =1 => mass of one molecule of water = 2.99*10-23. Am i correct this time? :smile:
 


Michael_Light said:
18/(6.02*1023)=2.99*10-23

Including units won't hurt and I have no idea what other numbers/rearrangements/symbols in your post mean - but this part looks OK.

After all, mole is just an overgrown dozen.
 
Last edited:


Michael_Light said:

Homework Statement



1) Haemoglobin contains 33% by mass of iron. Each molecules of haemoglobin has two iron atoms. Calculate the relative molecular mass of haemoglobin.

2) The relative molecular mass of water is 18.0. Calculate the mass of water molecule.

Homework Equations



Relative atomic mass of iron = 55.8, hydrogen=1, oxygen =16

The Attempt at a Solution



1) 1 mol of haemoglobin contains 2 mol of iron atoms, hence mass of iron in haemoglobin = 55.8*2= 111.6g. Iron occupies the mass of haemoglobin by 33%, so the mass of a haemoglobin = (111.6*100)/33 = 338.18g. => Relative molecular mass of a haemoglobin = 338.18 g/mol.

BUT the answer give by the answer sheet is 33818 g/mol. Can anyone correct my solution?

2) I have no idea on this. Can anyone explain to me how to get the answer? The correct answer is 2.99*10^-23 g.

Thank you for your help.
Michael_Light said:
I guess its 0.33%, they might have misprinted it...

1 mol of water = 6.02 x 1023 molecules
hence mass/18 = 6.02 x 1023 => mass = 18*6.02*1023= 1.08*1025. Please correct me...

The 'two' looks to be a misprint too. http://answers.yahoo.com/question/index?qid=20080828122411AAuf01x
 

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