# What is the procedure of designing a salt bridge for a galvanic cell?

I'm doing an experiment where I'm measuring the effect of changing the $\ce{Cu^{2+}}$ ion concentration on the voltage in a copper-zinc galvanic cell.

I'll be doing at least five trials for each of the five concentrations I'm testing for (from $0.2-1.0\:\mathrm{M}$), so in total that is 25 trials. However, do I need a new piece of filter paper as a salt bridge for each trial, or can I reuse the same piece of filter paper and dip it in a $\ce{KCl}$ solution each time? Do I really need to make 25 separate pieces of filter paper?

• Can you tell us why you want to avoid using 25 pieces of filter paper? It doesn't seem too excessive for the benefit of avoiding cross contamination. – bobthechemist Jun 13 '13 at 14:05
• I down voted your question because the title of the question in my opinion doesn't reflect the content. The question you are asking is in fact "Can I reuse a $KCl$ filter paper salt bridge more then once?" there is nothing about how to designing a salt bridge in what you are asking... – G M Feb 6 '14 at 18:45

If you wish to do 25 trials with 5 trials per concentration, I would suggest the following:

1. You can use the same filter paper as long as the $\ce{Cu^{2+}}$ concentration remains constant. However, since you are changing the concentration 5 times, you will need 5 pieces of filter paper.
2. After every trial, thoroughly wash the filter paper with distilled water.

So I would say you need at least 5 pieces, but you would not need to go all the way to 25 pieces. Just make sure to follow step 2 after each trial.

You might also want to consider using string as a disposable salt bridge. The general procedure would be to cut 6-8 inches of string, twist it and soak in the KCl solution.

do I need a new piece of filter paper as a salt bridge for each trial, or can I reuse the same piece of filter paper and dip it in a KCl solution each time? Do I really need to make 25 separate pieces of filter paper?

You need empirical evidence to resolve this question.

1. Perform entire experiment using 1 piece of filter paper dipped 25 times.
2. Perform entire experiment using 25 pieces of filter paper dipped 1 time.

If experiment #1 results differ greatly from experiment #2 then you cannot replace 25 pieces of filter paper dipped 1 time with 1 filter paper dipped 25 times.

Do not try to avoid scientific rigorousness. You're procedure should produce repeatable results.