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### Question L.35

Posted: **Wed Oct 04, 2017 11:57 pm**

by **Megan Purl 1E**

Can someone please help explain this problem to me. The question reads:

Sodium bromide, NaBr, which is used to produce AgBr for use in photographic film, can itself be prepared as follows.

Fe + Br2 --> FeBr2

FeBr2 + Br2 --> Fe3Br8

Fe3Br8 + Na2CO3 --> NaBr + CO2 + Fe3O4

What mass of iron, in kilograms, is needed to produce 2.50 t of NaBr?

### Re: Question L.35

Posted: **Thu Oct 05, 2017 12:15 am**

by **Emma Boyles 1L**

The problem involves going through each reaction and calculating the mass of Fe in steps.

First, you have to balance each of the three chemical rxns.

Then, you can calculate the number of moles you have of NaBr using its molar mass. Using the bottom chemical equation, determine how many moles of Fe3Br8 that can produce this amount of NaBr moles (in this case a 1Fe3Br8: 8 NaBr ratio so its the 1/8 of moles of NaBr).

Then using the second equation which Fe3Br8 is a product of, see how many moles of the reactant FeBr2 can yield the number of moles of Fe3Br8 you found from the step above^^^ (3 FeBr2:1 Fe3Br8).

Then, using the first balanced equation to see that there is a 1:1 ratio of FeBr2 and Fe you can see that the number of moles of FeBr2 you calculated in the previous step is equal to the number of moles of Fe required to produce that much.

You can multiply that amount of moles by the molar mass of Fe to get the mass of Fe needed!

Hopefully that all makes sense, sorry if the wording is confusing!

### Re: Question L.35

Posted: **Thu Oct 05, 2017 12:20 am**

by **aTirumalai-1I**

From my understanding, you have to work backwards from the third reaction. It is given that you have 2.50 t of NaBr. Using stoichiometric coefficients, you can find how much Fe3Br8 was needed to produce the 2.50 tons of NaBr. Once you find out how much Fe3Br8 you have, you can turn your attention to the second reaction and use stoichiometric coefficients to find how much FeBr2 was used to produce that Fe3Br8. Finally, with the amount of FeBr2, you can turn to the first equation and use stoichiometric coefficients to find out how much Fe was needed in the first place. Hope that clarified it a bit!