Purification of Copper Sulfate




In this instructable I am going to show you how to purify copper sulfate. The reason that I am doing this is because the type you get at the hardware store for cleaning drains has a fair amount of impurities in it. The stuff I got has about two percent impurities in it. This may not seem like very much, but when you are doing precise chemistry experiments it is really to impure to be used directly.

Now, there are several ways of purifying this stuff, but I am going to show you how to do it by recrystallization. The reason that I am going to show you this way is because it is the easiest way to do it in a home laboratory. The way this works is that all of the impurities will sink to the bottom of the beaker. the copper sulfate however will stay in solution and as the water evaporates the copper sulfate will crystalize on the seed crystal. This means that we can collect the crystals without getting the inpurities that have sank to the bottom.

DISCLAIMER: Copper Sulfate is dangerous. It can be harmful to you and can also be harmful to aquatic life if it gets is spilled and gets into water tables. 

Step 1: What You Need

Here are the tools/lab equipment you need:
  1. Beaker (I used a 400ml beaker but you could use a larger one if you want.)
  2. Spoon or Magnetic Stirrer
  3. Fan

Here are the materials I used:

  1. Copper Sulfate
  2. Water
  3. Popsicle Stick
  4. Thread

And that's all you need.

Step 2: Setting Everything Up

Now that you have all of your supplies together you can start getting things set up. The first thing to do is to measure out 400 milliliters of water. This is assuming that you are using a 400 milliliter beaker like I am, if you aren't measure out the appropriate amount of water to fill your beaker or jar to an inch bellow the top of the beaker.

Once you have your water measured out you need to assemble the string with your seed crystal. In my experiment I used a crystal that I had previously made as a seed crystal, but you can just use a string if you want. The seed crystal should be tied to a popsicle stick and suspended in the jar so that it is hanging in the middle. It is important that it is in the middle otherwise as the crystal grows it will bump into the sides of your beaker.

Step 3: Making the Copper Sulfate Solution

Now that your seed crystal is ready we are going to create the copper sulfate solution. But first I need to explain what a super-saturated solution is. A super-saturated solution is a solution that is holding as much of a dissolved substance as it can. In this experiment that substance is copper sulfate. One of the nice things about a super-saturated solution is that as soon as any of the water in the solution evaporates crystals will form. That will mean that in our super-saturated solution as soon as the water starts to evaporate copper sulfate crystals will form and we can collect these crystals because they are purer than the copper sulfate that we put in the solution.

Now that you understand how all of this works we are ready to create our super-saturated solution. Make sure that your seed crystal isn't in the beaker and then poor in your 400ml of water. After pouring in your water slowly add the copper sulfate one spoonful at a time. The solution will slowly get darker and darker blue. Keep adding and stirring until no more copper sulfate will dissolve. Once no more copper sulfate will dissolve the solution is super-saturated. Now put in your seed crystal and put it all somewhere that it won't be disturbed.

Step 4: Waiting

Now you need to put away your solution and forget about it. The solution will take several weeks to evaporate, but putting it next to a fan will help speed things up a little bit. I recommend putting the solution in a undisturbed place and letting it sit for a month.

Step 5: The Finished Product

After a month most of your solution should have evaporated. Now you are ready to collect your purified copper sulfate. Once your solution is evaporated the seed crystal should have grown considerably. There should also be a considerable amount of crystals formed in your beaker. The seed crystal is pure and so are the crystal on the sides of the beaker. When you are getting the crystals from the side of your beaker make sure not to accidentally get any from the bottom as they are impure.

Once you have collected all of the crystal that are pure you can st them out on a plate or watch glass to dry. And now you have purified copper sulfate.

Feel free to comment on any sugestions, questions, or anything else.

If you think this is worthy please cast me a vote in the shopbot and teacher challenge.




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    13 Discussions


    Tip 1 year ago

    This is not pure copper sulphate, it is most likely the pentahydrate. Anhydrous CuSO4 is white.


    Reply 3 years ago on Introduction

    i think that drives the water off too quickly and the crystals don't have time to form


    Do you know how to grow a fine seed crystal?

    I am having troubles on it.

    And I want a good way to display it.



    Reply 7 years ago on Introduction

    Thanks, I am glad you like it. I looked at that web site and it looks like they have some pretty neat experiments. I will try some of them. Here is another neat site.



    5 years ago on Step 5

    so if u want to turn copper sulphate solution into copper sulphate crystals u just have to evaporate or u can use sublimation


    5 years ago on Step 5

    so lets say u want to separate copper sulphate solution to turn it into crystals
    Would u just have to evaporate it alone


    Reply 6 years ago on Introduction

    Hmm. Thanks I didn't think to look there. I would have thought they couldn't ship, that since it is poisonous. Shows what I know. Hah



    6 years ago on Introduction

    Do you know how well this method works for purging that 2% of impurities?

    The seeds-on a string method is the most popular method for home crystallization, though it's actually pretty poor in terms of quality of output. You get all kinds of secondary nucleation sites which decrease the purity of the final product. Using fishing line is better than string or twine for this reason, but if you want ridiculous purity, do it like a process chemist (yes I am a process chemist and yes I'm tooting my own horn :P).

    Acquire or craft an overhead agitator and affix it such that the blades are not touching the bottom (stir bars grind the crystals and this can lead to erratic crystals). With stirring, get a saturated solution @ 50-60 deg C, let it cool rapidly 5-10 deg C, drop in your seed crystals, about 1% w/w loading, and small enough to remain in suspension, then cool the flask down from there. If you have temp control, cool it linearly or accelerating the cooling as it progresses, like a flipped exponential graph, or if you lack temp control, set it in a large pot of water as thermal mass and let it cool naturally after the seeding. The longer you can hold it at the temp at which you seed, the better.

    Filter, and wash the crystals with cold (preferably distilled or DI) water, you don't want the supernatant sticking to the outside of the crystals.