Posted by GP on Wednesday, January 7, 2009 at 9:41pm.
well its a double replacement first of all so they all switch
the way my teacher taught it was that NO3 and Cl are the 'girls' and the metals are the 'boys'
all elements to the right of the stair step on the periodic table are the girls. to the left the boys
anyways.. think of it as the two are pairs or dates :)
then they switch dates so Pb goes with Cl
and Li goes with NO3
each girl is with a boy
then you have to balance it
repost if u have any more questions
A little hard to explain in writing without a blackboard but here goes.
First, you need to know the kinds of reaction. I'm sure you have studied synthesis, decomposition, single replacement, etc. This one is a double displacement reaction. Look at the possibilities. Positive must go with negative; therefore, the only possibility is for the Pb(NO3)2 and LiCl to stay as they are (in which case we say there is no reaction) or to change partners. So how do you know they change partners. By looking at a table of solubilities? Here is a simple table.
Reading through the table tells you that Pb(NO3)2 is soluble. LiCl is soluble. PbCl2 is not soluble. LiNO3 is soluble.
There are several reasons that favor a reaction taking place.
a. A gas is formed. None of these are a gas.
b. A ppt (precipitate) is formed. PbCl2 is a ppt since it is insoluble; therefore, the reaction will occur.
3. A slightly ionized material is formed.
4. An oxidation/reduction reaction but this isn't one.
#3 occurs when an acid is added to a base.
HCl + NaOH ==> NaCl + H2O.
None are a gas, both NaCl (and of course) water are soluble, BUT H2O is a slightly ionized substance; therefore, the reaction occurs. I hope this helps but don't hesitate to ask a specific question about the explanation.
The two initial compounds are made of electrically charged particles, ions.
Pb(NO3)2 represents one Pb^+2 ion and two NO3^-1 ions.
LiCl represents Li^+1 ions and Cl^-1 ions.
When the two compounds are dissolved in water, any positive ion can associate with any negative ion in the solution.
Pb^+2 ions can pair up with Cl-1 ions to give PbCl2 which is neutral.
Li^+1 ions can associate with NO3^-1 ions to give LiNO3 which is also neutral.
To summarize, the positive ions from one ionic compound may combine with the negative ions of the other compound.
1. A reaction actually occurs if one of the new compounds has low solubility in water and precipitates to the bottom, or a molecular (not ionic) substance forms. If neither of these things happens, the reaction you write down is meaningless. No reaction occurred.
2. The prerequisite skills for this type of question are: Formula writing and naming, knowing and applying solubility rules, and balancing the equation after you figured out the formulas of the new compounds.
Thank you. My teacher hasn't really gone into much depth on types of reactions, just acids reacting with metals and water reacting with active metals.
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