Suppose a small amount of lead (ii) chloride got into your ba (oh) 2 sample before your titration, contaminating it. how do you think this contamination would affect your calculated concentration for the sample

Actually this depends on what kind of titration is being done. If we are titrating Ba (OH) 2 using an acid, it actually does not matter that some Pb (OH) 2 is formed because the acid will still neutralize even those OH - ions that combined with lead Pb.

But other than that, generally we can say that the calculated concentration can be affected because lead (II) chloride would co-precipitate with Ba (OH) 2 to form Pb (OH) 2