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    I'm trying to find the mass of iron in an iron tablet using a colorimeter. Please can somebody help me!

    I crushed an iron tablet, dissolved it in 20ml of 1M sulphuric acid. I then added potassium permanganate (about 4ml). I transferred this to a 250ml volumetric flask and made to the mark with water. I then took 5ml of this solution and added it to a 100ml volumetric flask and made this to the mark with distilled water. 10ml of this solution was transferred to a boiling tube and I added 10ml of ammonium thyocyanate.

    I used the colorimeter, made a calibration graph and found the concentration of the iron solution was 2x10-5M.

    But now I'm kind of stuck. What volume of iron do I use if I'm trying to find the number of moles in this iron solution?
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    (Original post by Holllyberry)
    I'm trying to find the mass of iron in an iron tablet using a colorimeter. Please can somebody help me!

    I crushed an iron tablet, dissolved it in 20ml of 1M sulphuric acid. I then added potassium permanganate (about 4ml). I transferred this to a 250ml volumetric flask and made to the mark with water. I then took 5ml of this solution and added it to a 100ml volumetric flask and made this to the mark with distilled water. 10ml of this solution was transferred to a boiling tube and I added 10ml of ammonium thyocyanate.

    I used the colorimeter, made a calibration graph and found the concentration of the iron solution was 2x10-5M.

    But now I'm kind of stuck. What volume of iron do I use if I'm trying to find the number of moles in this iron solution?
    Hey, this technique sure is complicated!
    I would start this by using the value of 10ml (or .01 dm^3) and the concentration you've given from the graph. Once you know the number of moles in this 10ml, you can work backwards to get the no. moles in the original solution!
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    (Original post by Serine)
    Hey, this technique sure is complicated!
    I would start this by using the value of 10ml (or .01 dm^3) and the concentration you've given from the graph. Once you know the number of moles in this 10ml, you can work backwards to get the no. moles in the original solution!
    Does this make sense to you?
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    (Original post by Serine)
    Does this make sense to you?
    How would I work backwards to find the moles of the original solution?

    I know what to do after I've found the number of moles, but this part is really confusing for me. Probably because I've been working on this project for hours and hours

    Thank you so much for replying
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    (Original post by Holllyberry)
    How would I work backwards to find the moles of the original solution?

    I know what to do after I've found the number of moles, but this part is really confusing for me. Probably because I've been working on this project for hours and hours

    Thank you so much for replying
    Hey, I wrote you out a solution that I seem to have misplaced :/ - is it okay if I get back to you tomorrow morning? A2 Biology is kinda taking over my life this evening? Just PM me in the morning!
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    The first thing to spot is how the value you've just calculated for moles is significant - if you know the number of moles in 10ml of solution (let's call what you've calculated M moles), then how many moles, M, are in 100ml of the solution you took the sample From?


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    (Just think about the moles=conc*volume calculation) if M/conc=10, and c is fixed, for M/conc=100 there must be 10M moles in the 100ml solution!


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    Can you see how to use this to calculate the moles in 250ml?


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    Using the same method we can say 10M because came from the 5ml sample you took from 250ml, and because you made that solution up to 250ml by dilution (not changing the no. of moles in the whole solution), then we have 10M*50 moles of iron in your 250ml solution!!


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