posted by Kid

Physical Developer (PD) is a set of solutions used to develop latent fingerprints on different porous and nonporous surfaces. It is often used to develop fingerprints on currency. Below are FBI recipes for PD. Solution 1 serves as a cleaning solution before using a mixture of solutions 2 and 4 in which the fingerprint is developed due to a redox reaction causing the deposition of metallic silver within the ridges of the fingerprint. Determine the concentration of each ingredient in the four solutions. The final volume for each solution is 1.00 L.

Solution 1: 25.0 g of maleic acid (C4H4O4)
Solution 2: 30.0 g of iron(II) nitrate [ Fe(NO3)2 ]
80.0 g of iron(II) ammonium sulfate [ Fe(NH4)2(SO4)2 ]
20.0 g of citric acid (C6H8O7)
Solution 3: 3.00 g of N-dodecylamine acetate (C14H31NO2)
4.00 g of synperonic-N (skip-this is a mixture)
Solution 4: 200.0 g of silver nitrate

I don't really know where to start in terms of calculations that would help in solving this problem. I can deduce that the metallic silver deposition in the ridges of the fingerprint would obviously contain Ag and an anion from one of the solutions (maybe solution 2). Thanks in advance for any help.

  1. DrBob222

    This is a very simple problem. I suspect you are getting trapped from all of the stuff that goes on before the question. Forget everything in the problem except the last two sentences; ie., Determine the concn of each ingredient AND the final volume in each is 1 L. All the rest is just to overwhelm you with information that is of no use..
    All are worked alike. Here is what you do.
    Step 1. mols of ech ingredient = grams/molar mass = ?
    Step 2. M = molarity = mols from step 1/1 L = ?

  2. DrBob222

    I also want to point out that the problem DOES NOT say what units are to be used for the concentration. i chose to do them by M because I'm sure that's what the author of the problem meant; however, note that for solution 1 you could have said that (maleic acid) = 25,0 g/L and that would be right. The others could be done similarily, also.

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