Hi! So I just tried this question on paper, and I have checked that my answer is in fact correct.
This is how I did it:
1. If 95% yield is going to give us 550g then we should know how much we are making at 100% yield as that is the real amount we will make in the reaction
2. To work out 100% yield, you can divide 550 by 95 then multiply by 100...should give you 578.94...
3.Now we use mole formula to work out the number of moles this 100% amount is
4. So do your answer for 100% yield divided by the molar mass of NaN3 which should be 65, and this should give you an answer of 8.906... moles
5. The ratio of NaNH2: NaN3 is 2:1, therefore, you should multiply your mole answer for NaN3 by 2 to get moles of NaNH2 you must make, you should get 17.81... moles
6. Now once again use mole formula to work out mass
7. Mass= No of moles x Mr so then you should be doing 17.81... x 78 to get 1389.47...
8. This answer is now your answer to 2NaNH2
9. We divide the answer by 2 because the ration there is 2:1 and we only want it for 1 moles
The final answer should be 694.7g
Sorry if this method is long winded or complicated, but this is how I approached it. Always make sure to keep your full answers in your calculator, do not round until the end because otherwise, your answer will not be accurate.