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Inorganic lab help; limiting reagents

Hi,

So i've generated the equation

Screen Shot 2018-02-18 at 14.06.56.png

I know this is 100% correct for the reaction I have done. During the experiment i used Iron(II) sulfate heptahydrate (2.80g, 10.1mmol), 2M
sulfuric acid (12 cm3, 24 mmol), Sodium diethyldithiocarbamate trihydrate (2.50 g, 11.0 mmol) , and sodium nitrite (0.38 g, 5.51 mmol).

Initially, i thought the sodium nitrite was the limiting reagent in the reaction, however, i am starting to question myself. Do the numbers in front of each formula in the equation make an impact in this matter? i.e. because we have 10.1 mmol of Iron(II) sulfate heptahydrate, are there actually 10.1/4 mmol in this reaction which would make it the limiting reagent?
Yes, the numbers in front matter - thats the reacting ratio
So in this case you are reacting 4:4:2:2
So 5.51 mmol is more than half of 10.1mmol, so it's not exactly a 4:2 ratio, you have slightly more sodium nitrate then you need
So yes, the Iron(II) is the limiting reagent
Original post by SassyPete
Hi,

So i've generated the equation

Screen Shot 2018-02-18 at 14.06.56.png

I know this is 100% correct for the reaction I have done. During the experiment i used Iron(II) sulfate heptahydrate (2.80g, 10.1mmol), 2M
sulfuric acid (12 cm3, 24 mmol), Sodium diethyldithiocarbamate trihydrate (2.50 g, 11.0 mmol) , and sodium nitrite (0.38 g, 5.51 mmol).

Initially, i thought the sodium nitrite was the limiting reagent in the reaction, however, i am starting to question myself. Do the numbers in front of each formula in the equation make an impact in this matter? i.e. because we have 10.1 mmol of Iron(II) sulfate heptahydrate, are there actually 10.1/4 mmol in this reaction which would make it the limiting reagent?


Your equation is incorrect, in fact the very first species is incorrect. Iron(III) sulfate does not have that formula... and as you state that it is iron(II) sulfate then your equation is far from 100% correct...

... closer to 0%
Reply 3
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SassyPete
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6
Original post by charco
Your equation is incorrect, in fact the very first species is incorrect. Iron(III) sulfate does not have that formula... and as you state that it is iron(II) sulfate then your equation is far from 100% correct...

... closer to 0%


My bad - there should be no 3 after the sulfate group in the iron complex
(edited 6 years ago)
Reply 4
Avatar for SassyPete
SassyPete
OP
6
Original post by SassyPete
I see what you mean, however, I was just going off what the lecturer had marked and said was correct - leading me to wonder why now. It seems to be correct with regards to people who did this experiment last term and had it marked too.

I will have to look further into this as now i am fairly confused


ah yes spotted the error on my behalf - accidentally copied formula from the equation editor on word without taking regard for the scenario - my bad
Original post by SassyPete
ah yes spotted the error on my behalf - accidentally copied formula from the equation editor on word without taking regard for the scenario - my bad


In any balanced equation you should not include water of crystallisation.

1. Identify the species oxidised
2. Identify the species reduced
3. Construct half equations for 1 & 2 above balanced for both atoms and charge
4. MTB suitable integers in 3 to equalise electrons
5. add half equations, gather terms and simplify

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