I'm going over some post-laboratory questions for Conductivity of Solutions.

One of the questions is...

From your measurements, what can you say about

a) the presence of ionic impurities in tap water?

b) the presence of molecular impurities in tap water?

I measured the conductance of deionized water to be 0.00 mS and the conductance of tap water to be 0.20 mS.

What kind of an answer is this question looking for?

1 answer

How large a number do you think 0.20 mS is (compare it with some of the measurements you made). The conductance is related to the number of ions in solution. That should be an indication of the number of ions in tap water.
For the second question, I don't think conductance measurements will tell you anything about the molecular composition since those molecules don't give you conductance (at least not unless they react with water). For example, remember that CO2 is a molecule and that reacts with water to produce a small amount H2CO3 which then ionizes VERY slightly to provide H^+ and HCO3^- ions. My answer to that part, I guess, would be "conductance measurements will not indicate information about the molecular composition materials dissolved in H2O unless the molecule reacts with water to form ions."