number of moles

[chris logan]

how exactly do yo find the number of moles of 1 element in a compound of a given weight

i know to convert mass to moles the given mass of the element is divided by the mass of one mole of the element.

 

[hypervalent_iodine]

This is probably best illustrated with an example question.

 

Assume we have, say, 180.16 g of glucose (C₆H₁₂O₆) and the question is asking you how many moles of carbon there is. To answer this you could approach it from a couple of routes, but the easiest way (IMO) is to first calculate how many moles of glucose we have in that 180.16 g. We use the following equation to solve this:

 

(1) n = m / MW

 

(where n is number of moles, m is mass and MW is molecular weight or molar mass)

 

MW for glucose is 180.16 g / mol, so plugging in the numbers to the above equation gives you 180.16 / 180.16, which comes to 1 mole.

 

To solve for the number of moles of carbon in the glucose sample, all you need to recognize is that there are 6 molecules of carbon for every 1 molecule of glucose (since it is C₆H₁₂O₆), which means that all you have to do is multiply the answer you got from (1) by 6. Similarly, if the question asked you for number of moles of hydrogen, you would multiple the same number by 12 and so on.

 

I hope that answers your question.

[chris logan]

thanks alot