[GoGoGadget]

1. Ten moles of N₂O₄(l) are added to an unspecified amount N₂₃(CH₃)(l) according to the equation shown below:

5 N₂O₄(l) + 4 N₂H₃(CH₃(l)  12 H₂O(g) + N₂ + CO₂(g)

If 23 moles of water are produced and the reaction runs to completion, what is the limiting reagent?

A) N₂S₄(l)

B) N₂H₃(CH₃)(l)

C) H₂O(g)

D) There is no limiting reagent.

I ended up getting an answer of C for this one, thinking that we could use the number of moles of H₂O and moles of N₂O₄ from the reaction to determine the amount of total N₂H₃ produced. However, in reviewing the answering for it, the rationale was that the correct answer was B since we weren't provided with a specified amount and that the reaction would have produced a total of 24 mol of H₂0 with N₂O but how can we assume this to be the case if we're not given a starting amount of N₂H₃?   


2. The following reaction is run to completion:

As₄O₆(s) + 6C(s)  As₄(g) + 6CO(g)

How much carbon is required to produce 75 g of arsenic acid?

A) 12 g

B) 18 g

C) 48 g

D) 72 g

This is how I went about trying to solve it:

75 g As x (1 mol As/300 g As) x (6 mol C/1 mol As) x (12 g C/1 mol C).

I'm not sure if this is the correct approach or not?

Any help is appreciated!

[Borek]

I ended up getting an answer of C for this one

C points to water which is a PRODUCT - so it can't be a limiting REAGENT.

However, in reviewing the answering for it, the rationale was that the correct answer was B since we weren't provided with a specified amount and that the reaction would have produced a total of 24 mol of H₂0 with N₂O but how can we assume this to be the case if we're not given a starting amount of N₂H₃?

How many moles of water would be produced if all 10 moles of N₂O₄ reacted? Did you got that much? If not - why?

How much carbon is required to produce 75 g of arsenic acid?

I don't see arsenic acid here.

75 g As x (1 mol As/300 g As) x (6 mol C/1 mol As) x (12 g C/1 mol C)

This will accidentally produce a correct number (assuming question was about arsenic, not arsenic acid), but if the reaction equation uses As₄, you should also use As₄ everywhere in your calculations.