[Kris44]

Hello, i have done the following reacting mass calculations and am not sure if they are correct.

1. What mass of Iron would be obtained from 160 tonnes of Iron(III) Oxide?

Equation = Fe₂0₃ + 3CO -----> 2Fe + 3CO₂
I did ratio =2/1 iron oxide . n= m/M = 160/160 = 1 Mmol
m=nM = M =1 X 112 = 112 tonnes

2.a) What mass of nitrogen is needed to produce 340g of ammonia?

Equation = N₂ + 3H₂ -----> 2NH₃
I did ratio =  1/2 n=m/M n= 340/34 = 10mol
10x1/2=5mol
5x28=140g

b) How much Hydrogen is required for 340g of ammonia i worked out 90g



 

[Borek]

1 OK, 2 wrong twice. In both cases I don't understand what you did so it is hard to tell why it is OK or why it is wrong.

What is molar mass of ammonia?

[Kris44]

Hi, for ammonia i did n=m/M therefore = 340g/34 = 10mol

[Borek]

What is molar mass of ammonia?

[Kris44]

34 gmol-¹

[Borek]

NH₃?

[Kris44]

17 gmol but in the equation there a 2 moles?

[Borek]

There are 2 moles in equation, and two moles mass is 34 grams, but molar mass of ammonia is 17 g. Note that you wrote something like 340 g = 10 moles - which is wrong, 340 grams is 20 moles. You must carefully separate molar mass from mass of product/substrate.

[Kris44]

Ok i was looking at examples in my chemistry book and it confused me a little so too work out molar mass of a compound i ignore the number in front of that compound? going back to the question then would it be 280g of Nitrogen and 60g of hydrogen?

[Borek]

Molar mass is a molar mass, number in front tells how many moles - so the totall mass is number in front times molar mass, OK?

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

going back to the question then would it be 280g of Nitrogen and 60g of hydrogen?

Yes. Depending on the accuracy of molar masses used you can be slightly off, but assuming N is 14 and H is 1 - you are OK.