500 gm zinc sulphate and 280 gm iron sulphate ( total weight 780gm ) were taken in flask and water is added to make final volume 1 liter. the solution is heated to dissolve the zinc and iron sulphate in water completely. after heating any water loss is compensated by adding water and making final volume to 1 liter. the problem is after cooling down the solution zinc and iron sulphate is getting recrystallize to some extent and crystals are settling down at bottom and side of flask. is there any chemical that can be added to prevent the recrystallization of salt. i want to keep the iron and zinc sulphate fully dissolved in water even after solution cools down.

any suggestions or help is appreciated.

  • $\begingroup$ The unit gram has the symbol g, not gm, similarly the kilogram has the symbol kg, not kgm. $\endgroup$
    – Poutnik
    Dec 9, 2023 at 8:57
  • $\begingroup$ It would not change the answer, but you have not specified the iron oxidation state and generally the hydrate form of both salts. $\endgroup$
    – Poutnik
    Dec 9, 2023 at 9:43
  • 1
    $\begingroup$ What a user asks about may confuse and hide what the user wants to do and what the user needs to know. A broader context, background, purpose could help in that. $\endgroup$
    – Poutnik
    Dec 9, 2023 at 10:20

1 Answer 1


It seems there is no way but using more water, as you try to violate their solubility at room temperature.

Note that both salts mutually suppress their solubility, that is usually published as $\pu{g/100 mL}$ of water.

The first effect decreasing solubility is the common sulphate anion, leading to lower equilibrium activities of cations, what means lower effective solubility. It is similar as decreasing of solubility of slightly soluble $\ce{PbCl2}$ by adding $\ce{NaCl}$ or $\ce{Pb(NO3)}$ to the solution.

The second effect is a general salt effect, as there is ion competition for being hydrated and dissolved.

There is possibility you could slow down the crystallization by addition of thickeners like ethylenglycol, glycerine, polyvinylalkohol or sucrose, but the addition would further decrease the solubility.

Another option worthy to try are surfactants.

In any case, additives may interfere with the purpose of the solution.


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