Mole Homework Help: Iron & Water Mass Calculation

[Michael_Light]

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.

 

[Borek]

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

How many molecules of water in 1 mole?

 

[Michael_Light]

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...

 

[Borek]

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?

 

[Michael_Light]

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?

M_r 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?

 

[Borek]

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.

 

[epenguin]

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.

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