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Homework Help: DOUBLE Replacement Reactions

  1. Oct 25, 2005 #1
    ^^Double Replacement Reactions^^
    NaOH+CuSO4 -> ?
    NH4I+AgNO3 -> ?
    K2CO3+ Ba(OH)2 -> ?
    KOH+ HI -> ?
    K2CO3 + HNO3 -> ?
    (NH4)2SO4+BaCl2 -> ?
    Na2S+ NiSO4 -> ?
    Pb(NO3)2+KBr -> ?
    Fe2(SO4)3 +Ba(OH)2 -> ?
    Hg2(NO3)2+KI -> ?
    Don't really get this...Please Help!
  2. jcsd
  3. Oct 25, 2005 #2
    Well I'm definitely not going to do this all for you, and your text should explain this anyways. This type of stuff should be posted in the homework section...

    Generally speaking for double replacement reactions:
    1) Break each species into ions.
    2) Switch the ions around so that new species form.
    3) Reaction will occur if there is a) formation of a precipitate b) formation of a gas c) neutralization. Otherwise the reaciton will not occur.
    4) Balance equation.

    Your first one:
    NaOH + CuSO4

    NaOH --> Na+ + OH-
    CuSO4 --> Cu+2 + SO4-2

    Switch them up so you have Na+ and SO4-2. Therefore you need 2 Na+ for one SO4-2: Na2SO4.

    And you're left with Cu+2 and OH_. You need 2 OH- for one Cu+2: Cu(OH)2

    This reaction occurs because Cu(OH)2 forms a precipitate (is mostly insoluble in water).

    Now balance your equation:

    2NaOH (aq) + CuSO4 (aq) --> Na2SO4 (aq) + Cu(OH)2 (s)

    When factoring binomials in algebra, you use FOIL method (first outside inside last). My chemistry teacher called this the "OI" method for outside inside. This might help you remember it.

    Things get more complicated with polyprotic acids and hydrolysis of transition metals.

    Also remember that carbonic acid is unstable so:
    H2CO3 --> H2O + CO2

    Other than that all of those are rather straightforward.
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