Question

how many grams of hydrogen make up 3.5 moles of glucose C6H6O6?
a 1.7g b 3.5g
c21.0g d 101.5g

Answer 1

You should calculate it by using the percentage by mass of the hydrogen atoms.
3.5mole of glucose is
3.5(12*6+1*6+16*6)g
=609g
==>ans:[(1*6)/(12*6+1*6+16*6)]*609=21g

ans is c.

Answer 2

you should know the formular to calculate all the question of the chapter of 'Reacting masses'.

eg. mass / molar mass=no of mole

no of mole*avagadros=no of particles

...and so on..

Answer 3

But since in each mole of the glucose, there's 6 moles of H atoms. So isn't it easier to just use 3.5 times 6?

Answer 4

my ans is just to show him the logic of calculate the chapter of reacting mass.and i agree that your method is absolutely good for MC question.

Answer 5

I would argue that this is a poor question because of the typo and poor wording. First, glucose is C6H12O6 so the molar mass is 180 and not 174. So the 3.5 moles glucose will provide 3.5 x 6 = 21 moles of H ATOMS. But due to poor wording in the problem, when I'm asked for moles hydrogen, that means moles H2 so I would have divided the 21 by 2 to obtain 10.5 moles H2 and that isn't one of the answers. The problem would be better to ask for moles hydrogen ATOMS. Then everyone knows what the problem is asking.