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LAB 3 - NaCl vs. KCl

Question: How well can two different salts be compared by measuring current if their molecular sizes are very similar?


Hypothesis:___________________________________________________________________

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Test: _____________________________________________________________________________

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Materials:
As in LAB 1 and including KCl (anhydrous), M.W. = 74.55

Procedure:
As in LAB 1 with the following modifications -

Since the molecular weights of NaCl (58.44) and KCl (74.55) are close, it is more difficult to obtain accurate measurements of current that discriminate between the two salts. You can use different strategies in having students tackle this problem -

  1. A "minimum" approach. Tell the students the basic problem as stated above and then tell them to "experiment" with any part of the procedure they wish in ways they think will give them accurate measurements. Or,

  2. You can be more explicit in your instructions. The students should be told to be as careful as they can possibly be in making up their solutions and making their measurements, to repeat any steps if necessary (NaCl and KCl are cheap), to try measuring larger volumes of the salts in the gel boxes or other means you can devise.

In either case, the students should amend their procedures to describe and explain exactly what they did, the procedures that did not work as well as those that did, that led them eventually to the results upon which they based their conclusions.

Data:
As in LAB 2. All measurements should be recorded and saved, including those for experiments that did not work.

Analysis/Conclusion:
As in LAB 2.


LAB 1     LAB 2     LAB 4     General Instructions


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