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Homework Help: What happens if a add the following acids

  1. Apr 16, 2005 #1
    Hey guys....Can someone please explain to me what the general affect of adding the following acids and bases to my original test on equilibrium where I had K2CrO4 and K2Cr2O7.

    Observations I had made...

    Solution of K2CrO4
    CH3COOH becomes orange
    H2SO4 becomes orange
    KOH stays yellow
    NH3 stays yellow
    Ca(OH)2 stays yellow
    C2H5OH no change

    Solution of K2Cr2O7
    CH3COOH stays orange
    H2SO4 stays orange
    KOH becomes yellow
    NH3 becomes yellow
    Ca(OH)2 becomes very pale
    C2H5OH no change

    so can someone please help explain to me what the general affect of the acids and bases are?

    Also, i've noticed that Ca(OH)2 hadlittle effect on the equilibrium. Why is that?

    Lastly, in what way does OH- affect the equilibrium? Does it affect it any way??

    thanks again for your help!
  2. jcsd
  3. Apr 16, 2005 #2


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    First, write down the reaction, preferably through latex.
  4. Apr 16, 2005 #3
    sorry I dont know latex....

    CrO2-4 (the 4 is under the 2-) / Cr2O2- 7 (the 7 is under the 2-)
  5. Apr 16, 2005 #4
    [ tex ] (CrO_4)^{2-} [ /tex ]

    If you take out the gaps in the tex tags, that will give you:

    [tex] (CrO_4)^{2-} [/tex]
  6. Apr 16, 2005 #5


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    I'm referring to the whole reaction, balanced, it should have been provided to you...wasn't it?
  7. Apr 17, 2005 #6
    H+ (aq) + 2CrO4 2- (aq) --><--- Cr2O72- (aq) +OH- (aq)
  8. Apr 17, 2005 #7


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    assuming that Cr207 is orange and Cr04 is yellow

    Adding the acid shifts the equilibrium to the right, thus adding any type of arrehnius acid (one that has an acidic proton) to a solution of Cr2072- intensify the orange color; the rate of formation of Cr207 should have increased relatively since the 0H- is consumed (the reverse reaction rate has decreased relative to the forward from equilibrium where the two rates were the same). Adding a base will cause it to react with the acid concentration, the same principle applies here.
  9. Apr 17, 2005 #8
    ohh yep that makes sense...thanks for u help GCT

    but what is the general affect?
  10. Apr 19, 2005 #9


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    well it depends on what the reaction is, acids and bases are treated just like any other compound in dealing with La Chatelier's principle. Perhaps I'm not understanding you correctly.
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