[EX5TASY]

Vitamin B12, cyanocobalamin, is essential for human nutrition. It is concentrated in animal tissue but not in higher plants. Although nutritional requirements for the vitamin are quite low, people who abstain completely from animal products may develop a deficiency anemia. Cyanocobalamin is the form used in vitamin supplements. It contains 4.34% cobalt by mass. Calculate the molar mass of cyanocobalamin, assuming that there is one atom of cobalt in every molecule of cyanocobalamin.

I am confused in this problem, because there's only one numerical value they give you... I don't even know how to go about approaching this. I'm not looking for any answers, but more of guidelines or hints on how to solve this problem. Cobalt is 58.93g.

 

[Licensed Criminal]

I think this may help... (I'm new to chemistry, so don't take my word for it  )

One mole of any substance (whether as single atoms or as molecules) contains 6.02 X 10²³ molecules/ atoms. This means that cyanocobalamin contains this many molecules, per mole (I think).

Using the information above, you can calculate how much one atom of Cobalt weighs (58.93/ 6.02 X 10²³ ). Once you've got the answer, you can multiply it by 6.02 X 10²³ (the amount of molecules in one mole of cyanocobalamin). This will reveal how much Cobalt there is (in grams) in 1 mole of cyanocobalamin, which is 4.34 % of the total weight.

Once again, I must stress that I'm just a newbie!

[Dan]

Yes, liscenced criminal has the right idea, although it is not necessary to convert to one molecule, stick with moles.

You have the mass of cobalt in one mole of vit B12 (58.93g), and you know that this mass accounts for 4.34% of the total mass. So you simply have to scale up the mass to find the total (100%) mass of the vitamin.

Note that once you have your molar mass, you can check the value (using wikipedia perhaps...) remember, your calculation is only accurate to three significant figures, so it won't be perfect.

[EX5TASY]

I think this may help... (I'm new to chemistry, so don't take my word for it  )

One mole of any substance (whether as single atoms or as molecules) contains 6.02 X 10²³ molecules/ atoms. This means that cyanocobalamin contains this many molecules, per mole (I think).

Using the information above, you can calculate how much one atom of Cobalt weighs (58.93/ 6.02 X 10²³ ). Once you've got the answer, you can multiply it by 6.02 X 10²³ (the amount of molecules in one mole of cyanocobalamin). This will reveal how much Cobalt there is (in grams) in 1 mole of cyanocobalamin, which is 4.34 % of the total weight.

Once again, I must stress that I'm just a newbie!

I'm still kinda confused. You say to multiply (58.93/6.02 x 10²³) by 6.02 x 10²³ again, which just cancels each other out...

Is it really that simple of a problem where it just basic ratio math? Here is what I did:

1) 1 mol Co  X  58.93g/mol  = 58.93g

2) 58.93gCo / X = 0.434

X = 1357.8 g/mol  ?

I know the answer is 1360g/mol , so would my answer be acceptable? Or did I just get lucky and it is a coincidence that my answer was very close?

[Borek]

Well, it is a simple ratio

molar mass of cyanocobalamine/58.93 = 100%/4.34%

solve for molar mass:

molar mass = 58.93*100/4.34 = 58.93/0.0434

[EX5TASY]

i feel really stupid for being confused on this for so long.. now i get it