Hey Ivo, can you tell me in detail how did you get the part in bold^^. I'm totally confused with this chapter. Also do you have any rules/notes based on this chapter. Your help is much appreciated!
OK, we know from the equation given, the mole ratio: 1 mole of magnesium reacted with 2 moles of ethanoic acid.
The amounts of substance actually used was: moles of magnesium = 0.125, moles of ethanoic acid = 0.2. But from above, you see the ratio 1:2. So here, we either divide 0.2/2=0.1 or multiply 0.125 by 2 = 0.25.
Either way, you'll find that the magnesium is in excess and the ethanoic acid the limiting reagent. Has this helped?
For the second part, we are also using the mole ratio from the equation where 2 moles of ethanoic acid gives 1 mole of hydrogen. We can't use the calculations for magnesium as this was in excess, so we use the limiting reagent (ie. ethanoic acid), so 0.2/2=0.1.
And no sorry, don't have any notes. I guess, as long as you can handle this question, I think you'll be fine. I don't think it gets any harder than this.