[kandyfloss]

Ok here is another question i'm stuck up with.I'm using the {Urgent} tag because i've a test tomorrow.

The red color of blood is due to haemoglobin.It contains 0.335% by mass of Fe. 4 atoms of Fe are present in each molecule of haemoglobin.If the atomic mass of Fe=55.84 g/mol estimate the molar mass of haemoglobin.

[pear]

When doing stoichiometric conversions, think "what do I need?"  Since the end-point needs to be "grams hemoglobin/mol," I'm going to invert the ".335g Fe/100g hem." the word-problem presents to have grams of hemoglobin in the numerator.  Then plug in what you have (keeping in mind that the numerator/denominator should cancel one of the preceding denominators/numerators).  And remember a mol has 6.022 x 10²³ molecules!


100g hem.      55.84g Fe                      1 mol Fe                        4 molecules Fe      6.022 x 10²³ molecules hem.
   .335g Fe         mol Fe           6.022 x 10²³ molecules Fe         1 molecule hem.                1 mol hem.


Good luck on the exam!