Notices
Results 1 to 4 of 4

Thread: Noob questions about silver nitrate photosensitivity

  1. #1 Noob questions about silver nitrate photosensitivity 
    Forum Freshman GreatBigBore's Avatar
    Join Date
    Feb 2010
    Posts
    70
    I'm taking Chem I at community college. We just did a lab on ionic compounds and solubility. We combined a bunch of aqueous solutions with others and watched for precipitation. I asked my professor why the silver nitrate solution is in a dark bottle, and the answer was that it decomposes when exposed to light. I've done some poking around trying to understand that more, but all I've found is an equation like:

    2AgNO3 -> 2Ag + O2 + 2NO2

    But that leaves me with questions: if the bottle were kept closed, would the decomposition be slowed? If the bottle were left open and in the dark, would decomposition occur anyway, but maybe more slowly? And is it visible light only? Presumably it's a range of wavelengths that would cause the decomposition; is it a broad range or very narrow? Thanks.


    The most exciting phrase to hear in science is not “Eureka” but “That’s funny...” -- Isaac Asimov
    Reply With Quote  
     

  2.  
     

  3. #2  
    Bullshit Intolerant PhDemon's Avatar
    Join Date
    Feb 2013
    Location
    Newcastle-upon-Tyne, UK
    Posts
    5,243
    In a clear bottle the reaction would not be slowed as it is not dependent on anything but light, the only way it would be affected in a bottle is if the decomposition was an equilibrium, if this were the case in a closed bottle the reaction would reach equlibrium and the amounts of reactants and products would undergo no further change (this is not the case for this reaction AFAIK). As for the wavelength range I can't give you any numbers but in silver halides and nitrate the photon excites an electron into a delocalised conduction band so I'm guessing there is a reasonable large range of photon energies above a critical threshold that will do the job.


    Reply With Quote  
     

  4. #3  
    Forum Sophomore
    Join Date
    Jan 2014
    Posts
    106
    Quote Originally Posted by PhDemon View Post
    In a clear bottle the reaction would not be slowed as it is not dependent on anything but light, the only way it would be affected in a bottle is if the decomposition was an equilibrium, if this were the case in a closed bottle the reaction would reach equlibrium and the amounts of reactants and products would undergo no further change (this is not the case for this reaction AFAIK). As for the wavelength range I can't give you any numbers but in silver halides and nitrate the photon excites an electron into a delocalised conduction band so I'm guessing there is a reasonable large range of photon energies above a critical threshold that will do the job.
    No Le Chatelier's Principle at play then do you think? I imagine that there would be a pressure increase on decomposition in a closed bottle. I'm not sure how far this principle can be stretched.
    Reply With Quote  
     

  5. #4  
    Bullshit Intolerant PhDemon's Avatar
    Join Date
    Feb 2013
    Location
    Newcastle-upon-Tyne, UK
    Posts
    5,243
    Le Chateliers principle will change the position of the equilibrium (compared to what it would be at atmospheric pressure) but equilibrium will still be reached at a certain pressure.
    Reply With Quote  
     

Similar Threads

  1. New mwmber here im a noob a fat noob
    By xDARTHWOLFx in forum Introductions
    Replies: 2
    Last Post: February 18th, 2013, 11:43 AM
  2. A Noob's questions about optics (1)
    By TheAccursed in forum Physics
    Replies: 8
    Last Post: January 26th, 2013, 11:48 AM
  3. Photosensitivity
    By josh hinds in forum Astronomy & Cosmology
    Replies: 3
    Last Post: November 8th, 2012, 08:03 PM
  4. Replies: 1
    Last Post: August 16th, 2011, 01:21 PM
  5. Noob questions ^^'
    By Mentak in forum Physics
    Replies: 7
    Last Post: June 1st, 2010, 01:39 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •