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I am planning an experiment for a school project. I have roughly 50 minutes (not including equipment preparations) to perform my experiment, which aims to experimentally verify how Ksp changes with temperature. Traditional methods such as oven drying would not work because it would take way too long for the sample to be dried. I don't have a specific compound in mind that I want use, but my thought process is as follows:

  1. Add a "poorly" soluble (Ksp on the order of 10^-2) compound to distilled water
  2. Stir either with flask or magnetic stir bar
  3. Vacuum filter the remaining solid
  4. Dry the sample within roughly half an hour, if possible
  5. Record the mass that was not dissolved, to get the mass that was dissolved and calculate Ksp from there

I don't have much experience in the lab, so I am looking suggestions of methods for quickly drying a sample. Would it be more effective to get the Ksp using another method, such as measuring the electrical conductivity of the solution, instead of getting the mass?

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  • $\begingroup$ What is the overall goal of the project? Is determing Ksp the only choice given to you? $\endgroup$
    – AChem
    Oct 16, 2022 at 3:27
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    $\begingroup$ Is applicable washing the solid sample by volatile solvent soluble in water (e.g. acetone) and then fast evaporation of the solvent? $\endgroup$
    – Poutnik
    Oct 16, 2022 at 3:49
  • $\begingroup$ @ Poutnik: I agree about acetone hoping the substance is inorganic. $\endgroup$ Oct 17, 2022 at 1:11
  • $\begingroup$ You can use an inorganic stable salt and then just put that and the filter paper in a muffle funrace. $\endgroup$ Oct 17, 2022 at 12:22
  • $\begingroup$ Is this a demonstration in front of people, or something you have to do from start to finish in 50 minutes? If the former, could you pre-dry a sample to move on to after showing how to do the wet part? $\endgroup$
    – Jon Custer
    Oct 17, 2022 at 15:54

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There is a more easy way of doing the project. This is an experiment which I did at the age of about 16 in a GCSE chemistry lesson.

Take a flask or large test tube, weigh it empty and dry. Now add to it either some potassium chlorate, potassium perchlorate or if you want a safer substance use benzoic acid. Add to the test tube a small known volume of water from a burrett. Now heat the test tube by placing it in a beaker of boiling water. Put a thermometer into the tube.

Let the mixture heat up, if the solid fully dissolves then take the tube out of the hot water beaker and put it in a test tube rack. Allow it to cool while watching it. Note the temperture at which the solid reappears. If the solid fails to dissolve then add another 1 ml of water and put it back in the hot water bath.

Each time you have determined the temperture at which the solid reappears note it in a note book and then add 1 ml more of water to the tube and keep repeating the heating up and the cooling down (with careful watching).

Now divide the mass of the solute by the formula mass to get the number of moles. Next for each entry in your notebook calculate the number of moles per litre of the solute.

Now plot a graph of the concentrations on the y axis against the temperture on the x axis. You should now have a graph of the solubility of the solute against temperture. You can use this to compute the solubility product at different tempertures.

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