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I need to make a melamine solution for my project right now. From SciFinder, I found the solubility of melamine in water is, 35g/L at pH=5, 262g/L at pH=4, and 1000g/L at pH=1~3. Therefore, I made the solution based on the following calculations and steps. However, what I got is totally solid. Could anyone help me find out what went wrong? Thanks!!!

1. To get a pH=4 solution. I used HCl to adjust the pH. Since the pKa of melamine is 5.66, at pH=4, most of melamine molecules are protonated. If the solution is saturated, [melamine]=262/126.2=2.08. (the molecular weight of melamine=126.2) And, based on its pKa, I got [protonated melamine]=2.04M, [unprotonated melamine]=0.4M. And, from this, the acid needed for this protonation is 2.04M (free protons=10^-4 M, which could be ignored, compared to 2.04M).

2. Then I made a solution based on this concentration. I saved some spaces for melamine since it's not dense and occupies some volume in the final solution.

3. I added melamine powder into the acidic solution and tried to use stir bar to mix.

4. And here comes the white solid. When I just added around 1/5 of the saturated level of melamine, it still didn't form a clear solution. You could see the powder in the beaker.

5. I tried to shake it under 37 degrees overnight, but it didn't work.

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# Melamine Solution

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