# 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. Commented Jun 13, 2013 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
Commented Feb 6, 2014 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.