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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Kris44 on November 06, 2007, 11:50:02 AM

Title: would someone mind checking my work?
Post by: Kris44 on November 06, 2007, 11:50:02 AM

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



 

Title: Re: whould someone mind checking my work?
Post by: Borek on November 06, 2007, 12:16:02 PM

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?

Title: Re: whould someone mind checking my work?
Post by: Kris44 on November 06, 2007, 12:21:16 PM

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

Title: Re: whould someone mind checking my work?
Post by: Borek on November 06, 2007, 12:57:21 PM

What is molar mass of ammonia?

Title: Re: would someone mind checking my work?
Post by: Kris44 on November 06, 2007, 01:24:40 PM

34 gmol-¹

Title: Re: would someone mind checking my work?
Post by: Borek on November 06, 2007, 06:22:46 PM

NH₃?

Title: Re: would someone mind checking my work?
Post by: Kris44 on November 07, 2007, 04:52:52 AM

17 gmol but in the equation there a 2 moles?

Title: Re: would someone mind checking my work?
Post by: Borek on November 07, 2007, 05:34:09 AM

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.

Title: Re: would someone mind checking my work?
Post by: Kris44 on November 07, 2007, 05:50:23 AM

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?

Title: Re: would someone mind checking my work?
Post by: Borek on November 07, 2007, 06:24:51 AM

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

Quote from: Kris44 on November 07, 2007, 05:50:23 AM

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.