Mole Homework Help: Iron & Water Mass Calculation

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    Homework Mole
In summary, Haemoglobin contains 33% by mass of iron. Each molecules of haemoglobin has two iron atoms. Calculate the relative molecular mass of haemoglobin. The relative molecular mass of water is 18.0. Calculate the mass of water molecule.
  • #1
Michael_Light
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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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  • #2


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

How many molecules of water in 1 mole?
 
  • #3


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:
  • #4


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?
 
  • #5


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:
 
  • #6


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:
  • #7


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
 

1. How do you calculate the mass of iron in moles?

To calculate the mass of iron in moles, you will need to know the molar mass of iron, which is 55.845 g/mol. Then, divide the given mass of iron by the molar mass to get the number of moles.

2. How do you calculate the mass of water in moles?

To calculate the mass of water in moles, you will need to know the molar mass of water, which is 18.015 g/mol. Then, divide the given mass of water by the molar mass to get the number of moles.

3. What is the formula for calculating the mass of a compound in moles?

The formula for calculating the mass of a compound in moles is: mass (g) = number of moles (mol) x molar mass (g/mol).

4. How do you convert between moles and grams?

To convert between moles and grams, you can use the molar mass of the substance. To convert from moles to grams, multiply the number of moles by the molar mass. To convert from grams to moles, divide the given mass by the molar mass.

5. Can you provide an example of calculating the mass of iron in moles?

Sure, let's say we have 10 grams of iron. First, we need to determine the molar mass of iron, which is 55.845 g/mol. Then, we can use the formula: mass (g) = number of moles (mol) x molar mass (g/mol). Plugging in our values, we get: 10 g = x mol x 55.845 g/mol. Rearranging the equation, we get: x = 10 g / 55.845 g/mol = 0.179 mol. Therefore, the mass of iron in moles is 0.179 mol.

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