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Homework Help: Net ionic equations

  1. Apr 9, 2005 #1
    hi, i'm studying for the chemistry SAT and have a question that I'm not sure that ive done right...can someone please check my answer...thanks in advance!

    Write a net ionic equation for the following:

    a) Chromium dipped into silver nitrate
    b) Aluminmum dropped into a bath of sulphuric acid
    c) Zinc dipped into a solution of led (II) nitrate

    answers:

    a) Cr(s) + Ag+ (aq) --> Cr2+ (aq) + 2Ag (s)
    b) d)Al3+ + H2SO4 --> Al2(So4)3 + H2
    c) Zn2+ + Pb(NO3)2 --> Zn(NO3)2 + Pb2+

    im not sure if I have to have the (s), (aq) etc....

    can someone correct my answers if they are wrong...

    thanks again
     
  2. jcsd
  3. Apr 9, 2005 #2
    A looks right. You have state symbols missing from B and in an ionic equation the hydrogen ions are not changing so are not needed (I believe). C also has no symbols and again the lead is not really changing for an ionic equation.

    The Bob (2004 ©)
     
  4. Apr 9, 2005 #3
    my friend helped me get a...the answers for b and c are mine...I still dont get it...can you please show me?
     
  5. Apr 9, 2005 #4
    someone please my test is on thursday i need to study!! Thanks guys
     
  6. Apr 9, 2005 #5

    dextercioby

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    [tex] 2\mbox{Al}_{(\mbox{s})}+6\mbox{H}^{+}_{(\mbox{aq})} \rightarrow 2\mbox{Al}^{3+}_{(\mbox{aq})}+3\mbox{H}_{2}\uparrow [/tex]

    (sulphate ions are spectators)

    [tex] \mbox{Zn}_{(\mbox{s})}+\mbox{Pb}^{2+}_{(\mbox{aq})}\rightarrow \mbox{Zn}^{2+}_{(\mbox{aq})} +\mbox{Pb}\downarrow [/tex]

    (nitrate ions are spectators)


    Daniel.
     
  7. Apr 9, 2005 #6

    dextercioby

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    And the first one needs another 2.It should read

    [tex] \mbox{Cr}_{(\mbox{s})}+2\mbox{Ag}^{+}_{(\mbox{aq})}\rightarrow \mbox{Cr}^{2+}_{(\mbox{aq})}+2\mbox{Ag}\downarrow [/tex]

    (Nitrate ions are spectators)


    Daniel.
     
  8. Apr 9, 2005 #7
    b. aluminum into sulfuric acid
    If I remember how to do these correctly:
    [tex] 2Al + 3H_2SO_4 \rightarrow Al_2(SO_4)_3 + 3H_2 [/tex]

    Break it down into its compounds:

    [tex] 2Al + 3H_2^+ + 3SO_4^{2-} \rightarrow Al_2^{3+} + (SO_4)_3^{2-} + 3H_2 [/tex]

    Look on both sides to see if anything is idle during the process. It looks like everythings reacting, even the hydrogens look like theyre doing something, since they go from [itex] H_2^+ \rightarrow H_2 [/itex].

    I would go to http://www.towson.edu/~ladon/netionic.html for some more help.

    edit: Sulfate is spectating as dex said, i didnt see the coefficient. Cros it out
     
  9. Apr 10, 2005 #8

    dextercioby

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    The net charge in your equation,in the form written,doesn't add to zero in any of the 2 members,though it should...U have 6 protons from 3 sulphuric acid molecules...They're not 3 molecule-ion of Hydrogen...They have total charge "6+",and not "3+" as your notation would assume...

    Daniel.
     
  10. Apr 10, 2005 #9
    So in this case you would write H as a single atom and not a diatomic? theyre teaching us to always write the diatomics as diatomics. My notation is probably unorthodox but when I counted it it added up right.

    [tex] 2Al + 3H_2^+ + 3SO_4^{2-} \rightarrow Al_2^{3+} + (SO_4)_3^{2-} + 3H_2 [/tex]

    Left:
    2Al = 0
    3H_2 += +6
    3SO_4 2- = -6

    Right:
    Al_2 3+= 6+
    SO_4 _3 2- = 6-
    H_2 = 0
     
  11. Apr 10, 2005 #10

    dextercioby

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    That is not diatomic (in the LHS),it's simply 2 [itex] \mbox{H}^{+} [/itex] ions (protons) involved in a chemical bound (covalent,but here we're interested in ionic reactions,though the chemical bounds are not necessarily ionic) with 2 atoms of oxygen from the 4 involved in the sulphate ion...

    Notation is essential only when it's wrong.

    Daniel.
     
  12. Apr 10, 2005 #11
    Ok I see where I went wrong, thanks. Learn from my mistakes joejo :)
     
  13. Apr 10, 2005 #12
    no u've totally lost me whos right...whozum or dexter...

    dexter your right, right??
     
  14. Apr 10, 2005 #13

    dextercioby

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    >50% of the time,this one included :wink:

    Daniel.
     
  15. Apr 10, 2005 #14
    thanks guys...


    i dont get u dexter...are you saying ur guessing?
     
  16. Apr 10, 2005 #15
    dexters always right.
    he has a phd in everything.
     
  17. Apr 10, 2005 #16
    thank alot guys
     
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