Fundamentals

Chemical reactions involve changes - changes of reactants into products. Basic chemical reactions can be grouped into categories based on the types of changes that are occuring during the reaction. There are five basic categories - synthesis, decomposition, combustion, single replacement, and double replacement. If you know the type of reaction that reactants will involve themselves in, then you can predict the products that will be produced as the result of that reaction.
 

There are two questions in this Question Group. The two questions are very similar or are the same type of reaction The question below is one of the questions.

Version 1:

Potassium iodide and lead(II) nitrate undergo a double replacement reaction. Predict the formulae of the two products of the reaction.
 
K2Pb and INO3
KNO3 and PbI2
KPb and I(NO3)2
K(NO3)2 and PbI
K(NO3)2 and PbI2
 

How to Think About This Situation:

To be successful with this question, you need to understand what a double replacement reaction is, how to write formulas for ionic compounds, and  how to balance a chemical equation.  

A double replacement reaction involves the reaction of two ionic compounds to form two different ionic compounds.  The positive ion in one compound replaces the positive ion in the other compound. When the reaction is over, the cations have replaced each other in the other formula. The generic equation for such a reaction is ...
AB  +  CD  ==> AD  +  CB
 
Here A, B, C, and D are fictional elements or ions. A and C are the metal elements  or positive ions. B and D represent nonmetals or negative ions.  You will notice that A was orginally paired with B on the reactant side; but on the product side A is paired with D. Similarly, the positive ion C starts with the anion D on the reactant side but finishes paired with B on the product side of the equation. As such, A and C have switched places. You need to ....

Analyze the two reactants in your equation and identify the formulae of the two cations (positive ions) in the reactants. Also identify the formulae of the two anions (negative ions). Then to determine the products, switch the cations to the other anion. You'd be wise to use some paper, write some formulae down, and take your time. A minute spent writing down some formulae for the cations and anions will both build some good skill and probably save you time and frustration as you attempt to get this question correct. Determining the formulae for the products is going to require some good skill in and of itself. Use the link below to assist with the determination of the formulae.
 
 

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