If the reaction of 4.50 moles of sodium with excess hydrofluoric acid produced an 85.0% yield of hydrogen gas, what was the actual yield of hydrogen gas?

Unbalanced equation: Na + HF “yields”/ NaF + H2

1.91 mol H2

2.25 mol H2

2.65 mol H2

3.82 mol H2

Question

If the reaction of 4.50 moles of sodium with excess hydrofluoric acid produced an 85.0% yield of hydrogen gas, what was the actual yield of hydrogen gas? 

Unbalanced equation: Na + HF “yields”/ NaF + H2

 1.91 mol H2

 2.25 mol H2

 2.65 mol H2

 3.82 mol H2

aaronq · Answer

find the theoretical yield, multiply it by 85%.

anonymous · Answer

can you help me find the theoretical yield?

aaronq · Answer

First you need to balance the equation. Then use a ratio of the moles of the limiting reagent (sodium in this case) and the moles of product with their stoichiometric coefficients.

$\sf \dfrac{moles~of~Na}{Na's~coefficient}=\dfrac{moles~ofH_2}{H_2's ~coefficient}$

anonymous · Answer

Because I got 4.536 and I am not sure if that is the theoretical yield.

aaronq · Answer

that's not right

aaronq · Answer

Post what you did and i can check it

anonymous · Answer

Then tell me if I balanced the equation right. I put 2Na + 2HF "yields" 2NaF + H2

aaronq · Answer

yes, it good

anonymous · Answer

Then I put the moles that are given 4.50 mol Na x 1mol H2/2mol Na x 2.016 H2/1mol h2, which got me 4.536

aaronq · Answer

where did the 2.016 come from?

anonymous · Answer

There are two Hydrogen so I grabbed 1.008 and added 2 of them together

anonymous · Answer

1.008 G i mean

aaronq · Answer

that's the molar mass, were not interested in finding the mass 

note that the answers are given in moles

anonymous · Answer

oh okay can you help me solve the equation because finding the theoretical and actual yields are very hard for me to understand.

aaronq · Answer

you pretty much had it

$\dfrac{4.5}{2}=\dfrac{moles~of~H_2}{1}$
 
moles of $H_2=\dfrac{4.5}{2}=2.25~moles$    (this is the theoretical yield)

Then find what 85% of this is

aaronq · Answer

Usually the percent yields are in terms of mass (grams) but you should always check the units given in the options (if there are)

anonymous · Answer

Oh my god thank you very much. How long will you be online Because I may need help in a little bit and I would love to be able to reach out to you for help.

anonymous · Answer

I may need help with a few more questions is what I meant to say

aaronq · Answer

I'm on often, i can't say how long exactly. But there are other people here who can help you as well.

anonymous · Answer

Well then is it okay if you help me with another question of finding the theoretical and percent yields?

aaronq · Answer

sure post it !

anonymous · Answer

On the same question or as a new post?