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Why use Concentrated Ammonia in Colorimetry? watch

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    Hi,
    I have done a colorimetry experiment with various concentration of Cu2+ ions but when the [Cu2+] was very diluted (1/100 of standard) my teacher told me to add concentrated ammonia before measuring the absorbance reading why is that necessary and what is the chemical theory behind it?? I have to do a write up about it so any help would be really appreciated
    Thank you
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    (Original post by Tajwar786)
    Hi,
    I have done a colorimetry experiment with various concentration of Cu2+ ions but when the [Cu2+] was very diluted (1/100 of standard) my teacher told me to add concentrated ammonia before measuring the absorbance reading why is that necessary and what is the chemical theory behind it?? I have to do a write up about it so any help would be really appreciated
    Thank you
    Hi, I think that this woudl get a better responce in Chemistry then general A-levels
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    (Original post by Aph)
    Hi, I think that this woudl get a better responce in Chemistry then general A-levels
    I tried that in the first place it didn't work, it said "oops something is wrong please try again" but when I changed the category to A-levels it let me submit :/
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    (Original post by Tajwar786)
    I tried that in the first place it didn't work, it said "oops something is wrong please try again" but when I changed the category to A-levels it let me submit :/
    Gingerbread101 can you help us out?
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    (Original post by Tajwar786)
    I tried that in the first place it didn't work, it said "oops something is wrong please try again" but when I changed the category to A-levels it let me submit :/
    (Original post by Aph)
    Gingerbread101 can you help us out?
    Moved to the Chemistry forum for you :yy:
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    (Original post by Gingerbread101)
    Moved to the Chemistry forum for you :yy:
    Cheers for that.... hopefully I get a reply.. its quite urgent my coursework is due this coming monday
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    (Original post by Tajwar786)
    Hi,
    I have done a colorimetry experiment with various concentration of Cu2+ ions but when the [Cu2+] was very diluted (1/100 of standard) my teacher told me to add concentrated ammonia before measuring the absorbance reading why is that necessary and what is the chemical theory behind it?? I have to do a write up about it so any help would be really appreciated
    Thank you
    Concentrated ammonia reacts with copper ions forming a tetrammine complex, which is deep blue in colour. This allows easier detection by colorimetry, particularly in weak copper solutions with little absorbance.
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    Because why not.
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    (Original post by Mystery.)
    Because why not.

    You have any idea of the chemical theory behind this??
    Its quite urgeent.
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    (Original post by Tajwar786)
    You have any idea of the chemical theory behind this??
    Its quite urgeent.
    Read my previous post!
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    (Original post by Tajwar786)
    You have any idea of the chemical theory behind this??
    Its quite urgeent.
    Sorry,lol
    I can only think of what charco has already said..
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    Because conc ammonia stinks to high heaven and you don't like your lab partners?

    Then again, colorimetery is a fairly silly way of determining conc if pretty dilute. Much better to titrate, IMO.

    Add some KI, then titrate against S2O32-
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    (Original post by Pigster)
    Because conc ammonia stinks to high heaven and you don't like your lab partners?

    Then again, colorimetery is a fairly silly way of determining conc if pretty dilute. Much better to titrate, IMO.

    Add some KI, then titrate against S2O32-
    I have also done titration,electrochemical cell and gravimetric its part of the coursework to try as many experiments as possible to work out the conc of Cu (II) in a solution.

    But my point is what is the chemical theory behind adding the concentrated ammonia any ideas???
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    (Original post by Tajwar786)
    I have also done titration,electrochemical cell and gravimetric its part of the coursework to try as many experiments as possible to work out the conc of Cu (II) in a solution.

    But my point is what is the chemical theory behind adding the concentrated ammonia any ideas???
    I've already posted it!!!
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    (Original post by charco)
    I've already posted it!!!
    No you didn't.

    besides this reply wasnt to you anyways
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    [Cu(H2O)6]2+ is arather pale blue, esp. at low conc.

    [Cu(H2O)6]2+ + 4NH3<-> [Cu(NH3)4(H2O)2]2+ + 4H2O

    [Cu(NH3)4(H2O)2]2+is a deep blue colour and will absorb more strongly than [Cu(H2O)6]2+ making the colorimetry more sensitive.

    Basically what charco said.
 
 
 
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