Homework Help: Chemistry

Posted by TJ on Wednesday, January 23, 2008 at 12:52pm.

Which two solutions, when mixed together, will undergo a double replacement reaction and form a white, solid substance?

1. NaCl(aq) and LiNO3(aq)
2. KCl(aq) and AgNO3(aq)
3. KCl(aq) and LiCL(aq)
4. NaNO3(aq) and AgNO3(aq)

I know the answers 2 but I have no idea why.. thanks.

Chemistry - DrBob222, Wednesday, January 23, 2008 at 12:59pm
You need to know (and remember) the solubility rules and a couple of other points.
In general, reactions occur for one of three reasons.
a. a gas is formed. Do you know the common gases?
b. a precipitate (and insoluble material) is formed. Do you know the solubility rules?
c. a slightly ionized material is formed. Do you know the weak acids, weak bases, and any other weak electrolytes.

In this question, 2 is the answer because AgCl is formed and that is a white ppt. (rule b in the list of three above). Here is a site that gives the solubility rules.
http://www.chem.vt.edu/RVGS/ACT/notes/solubility_rules.html

I can help, also, if you don't know a or c in the list above. Let me know.
- Chemistry - TJ, Wednesday, January 23, 2008 at 1:06pm
  A little beyond what we're learning yet it still helped.. thank you !
  Could you by any chance give me a list of gasses at STP?
  - Chemistry - DrBob222, Wednesday, January 23, 2008 at 1:41pm
    Elements: Look at the periodic table to see where these are located.
    Hydrogen
    Nitrogen
    oxygen
    Fluroine
    Chlorine
    rare gases (He, Ne, Ar, Kr, Xe, Rn) but these are rarely produced in CHEMICAL reactions.
    
    common compounds:
    ammonia, NH3
    carbon dioxide, CO2
    carbon monoxide, CO
    sulfur dioxide, SO2
    sulfur trioxide, SO3
    nitric oxide, NO
    nitrous oxide, N2O
    nitrogen dioxide, NO2
    nitrogen pentoxide, N2O5
    nitrogen trioxide, N2O3
    ozone, O3 (technically not a compound)
    fuels such as methane, ethane, acetylene, etc.
    I see I didn't name by the new rules; i.e., N2O would be dinitrogen monoxide and N2O3 would be dinitrogen trioxide.
    
    For rule c I gave you in the last post, weak acids and weak bases will have an ionization constant (Ka or Kb) and those will be listed in tables. If they are not listed in the Ka or Kb tables they are strong acids or bases. It is easier to list the strong ones. HCl, HBr, HI, H2SO4, HNO3, HClO4, HClO3, are the common strong acids. Common soluble strong bases are KOH, NaOH, (all group IA hydroxides) and Ca(OH)2, Ba(OH)2, Sr(OH)2. MOST others are weak.
    Add water to the list of weak electrolytes above. It won't be listed in the Ka or Kb tables but it only weakly ionized.
    I hope this gets you one jump ahead.
    Come back and see us.

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