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My science project specifies me to make seed crystals of copper sulfate. We must use the powder form to make seeds. There are two types of copper sulfate pentahydrate; one is granular form (small seeds), and the other one is powder form. We must produce crystal seeds from copper sulfate (powder form). We are not allowed to use the granular form, because it forms seeds on its own already.

Steps I have taken:

  1. I saturated 50 ml of distilled water (room temperature) with copper sulfate pentahydrate (powder form).
  2. I added about 15 ml of purified sulfuric acid to the mixture, so it prevents the hydrolysis with water.This purified sulfuric acid I got from boiling battery acid. I boiled about 50 ml of batter acid (sulfuric acid mixed with ionic water). I waited till it reached about 15 ml (water evaporation). The fumes were getting strong at that stage. I'm not sure if purified enough.
  3. I then again mixed more copper sulfate to the mixture, and stirred it very well.
  4. I put the china dish (mixture) on a hot plate, and waited for it to reach crystallization point, while stirring it very well. 5 I know the water has to evaporate for the mixture to produce seed crystals. I waited for the mixture to evaporate about to 20 ml.
  5. I had no results.

I'm not sure what I'm doing wrong. I'm doing my project according to this video which I found on youtube. It is a very short video, and my main problem is the sulfuric acid part.

https://youtu.be/SAU-gptAFe0

Help.

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  • $\begingroup$ See, "no results" leaves an awfully broad field to our imaginations. What exactly happened? Copper sulfate never crystallized? Or it crystallized back into powder form? Or it turned into a brown goo? Or it magically vanished from the dish? Or the dish itself got stolen? $\endgroup$ – Ivan Neretin Feb 21 '17 at 10:26
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    $\begingroup$ It turned into white powder. As the water evaporated in low fire, it accumulated a white residue at the bottom. Yes, the copper sulfate never crystallized. $\endgroup$ – Arch Alegre Feb 21 '17 at 10:30
  • $\begingroup$ Aha! That's much better. So it did crystallize after all, only in a wrong form (not the pentahydrate we're after). Now try adding less acid and applying way less heat. The solution must not be nearly boiling; just moderately warm. Yes, it is going to take quite a while (a few hours, maybe). No, you don't have to stir it all the time. $\endgroup$ – Ivan Neretin Feb 21 '17 at 10:31
  • $\begingroup$ Alright. I will try it soon (tomorrow). Please, stay put. Thank you for your help. $\endgroup$ – Arch Alegre Feb 21 '17 at 10:33
  • $\begingroup$ Yeah, I believe I have to lower the heat much more, and mix maybe 5 ml of sulfuric acid (from battery acid). Sources say battery acid is about 35% sulfuric acid and the rest is just ionized water. So, I think I'm doing the purification correctly. I stop the boiling of sulfuric acid, when I can smell the weird acidic fume. Im boiling 50 ml of battery acid, and turning the boiling off at 15 ml about. I think I'm on the right track, just measurement as you say. I will do it tomorrow. $\endgroup$ – Arch Alegre Feb 21 '17 at 10:43
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Frankly you're going about this all wrong. First you want to exploit the difference in solubility of the salt in hot water versus cold water.

Copper sulfate's solubility is 32 g/100ml water at 20 C, and 114 g/100ml water at 100 C.

2-3 drops of sulfuric acid is all that is needed. You're just trying to prevent the formation of $\ce{Cu(OH)2}$ or $\ce{CuCO3}$.

I'm not sure about battery acid. I assume that you're using new battery acid, not actually from an old battery. So the sulfuric acid will be a little less concentrated. Use 5-6 drops instead of 2 or 3.

After you make a saturated solution of the copper sulfate (aim for 100g /100ml water) in hot water, let it cool slowly and don't stir at all. Stirring will promote nucleation of many small crystals.

To get a really large crystal you'd make a saturated solution at room temperature, filter it, and add one of these seed crystals. You'd then let the water evaporate over weeks very slowly.

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  • $\begingroup$ Yes, I'm using a new battery acid (Autozone). It is for motorcycles. I'm assuming that all batter acid has the same make up; 35% (about) sulfuric acid, and 65% ionized water. I do not think batter acid has any more additives added to this mixture. I have researched quiet a lot about battery acid, I'm pretty sure it is only sulfuric acid mixed with ionized water. Do you think it could have any additives? I hope not. And if so, what could I use to purify the sulfuric acid completely? The 15 ml of the sulfuric acid, which I purify, changes color to transparent goldish a bit. $\endgroup$ – Arch Alegre Feb 21 '17 at 15:58
  • $\begingroup$ @ArchAlegre - You don't need to "purify" it. You're adding it to water, Just use a little bit more. Acid that concentrated is nasty stuff. Be sure to wear eye protection when using it. // Acid from a used battery would have lead in it... $\endgroup$ – MaxW Feb 21 '17 at 16:04
  • $\begingroup$ Yes, it is new battery acid. I turn off the heat plate at about 15 ml from 50 ml. The fumes are acidic strong, so, I imagine that it must be a signal that the sulfuric acid is concentrated. I will do as you say: I will add 2 - 3 drops of it when I redo the experiment. $\endgroup$ – Arch Alegre Feb 21 '17 at 16:09
  • $\begingroup$ Experiment was a success. Thank you very much for your input. I just have one more question: why is sulfuric acid added to the solution? what is its role exactly? $\endgroup$ – Arch Alegre Feb 22 '17 at 12:46
  • $\begingroup$ @ArchAlegre - Noted why in 3rd paragraph of my answer... $\endgroup$ – MaxW Feb 22 '17 at 13:17

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