Cobalt chloride (CoCl2) has a dramatic color change when combined with water, making it a great water indicator. A concentrated solution of cobalt chloride is red at room temperature, blue when heated, and pale-to-clear when frozen. The cobalt chloride we’re using is actually cobalt chloride hexahydrate, which means that each CoCl2 molecule also has six water molecules (6H2O) stuck to it.

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23 Responses to “Cobalt Colors”

  1. you can also color with a white crayon and paint over it with water colors if you can’t do this.

  2. you can also color with a white crayon and paint over it with water colors.

  3. Hi Kim,

    Yes, you’re right – chemistry is one of the areas of science where it does add up if you’re not specific about what goal you’re trying to accomplish.

    Here’s how my program works: Unit 3 is for parents who only want to do a couple of experiments using mostly household materials. Unit 8 is for parents who want to do just the basics of chemistry and want to get just one kit (at the time, they used to include everything in that kit, but over time they’ve left out more and more, which is why there’s an additional shopping list for that unit). Unit 15 is for parents that really need to do a lot of chemistry (Jr High and HS level) and most of it comes in the kit (again, the kit manufacturers changed what they include, which is again less than they used to, so I made a supplement list to include everything that used to be in the kit). And I am putting together a HS level Chem in the Advanced Section here:

    So long story short, first, you need to find out what your educational goals are for your child. And yes, building up slowly is a great way to go – that way, you’re also sure that you’ll continue with it before making a big investment. If you know you’re going to continue with chemistry long term, I would suggest investing in a set of glassware and standard chemicals that you can use beyond my course. Parents that use this program have reported back that they found a lot of useful chemistry glassware and equipment from folks who are finished educating their kids, and also from high schools/local colleges in their chemistry department, so don’t feel that you have to get everything new. I’ve sourced the least expensive options for you to purchase this type of equipment and materials.

    Also if you find an experiment that you can’t source the chemicals for (or they are too expensive), you can so what my other students in more remote areas so – they watch the experiment and use that as their lab, and then work through the worksheets that way.

    I hope these help you determine what you’d like to do. Most of the items I have suggested purchasing will serve for 3-4 kids going through the program (or running through the experiment several times) so you don’t have to worry about making mistakes or using too much of something and running out.

  4. Kim Parent says:

    We are in 7th grade but haven’t done any chemistry yet so I thought I would start with 5th grade chemistry and try to get to a 7th grade level by the end of the year. I am struggling to make a shopping list for this. If I go to the Unit8 Chemistry page it is large and expensive if I add up the chemicals and the glassware. I thought about just choosing some experiments and buying what is needed per experiment. Then I noticed that the Cobalt needed for this 5th grade experiment is in the advanced chemistry set (Apologia Advanced Chemistry Lab Kit) you recommend for unit 8. You also recommend getting the C3000 chemistry kit to include glassware. Yikes, now we are looking at around $200.00. What are your thoughts or suggestions? Can I build a gradual chemistry set or will I have duplicate chemicals since I will need to eventually buy a chemistry kit?
    I intend to homeschool through high school so should I just invest in a large, all inclusive chemistry kit? It is an investment.
    Thank you.

  5. Either one is fine – for younger kids, you might prefer the plastic ones, and they’re made of a material that doesn’t stain easily so you can use either pretty successfully.

  6. Lauren Miller says:

    Would you recommend purchasing plastic or glass test tubes?

  7. doris rego says:

    where do i get cobalt chloride?

  8. Denatured alcohol is ethyl alcohol, but it contains additives. You can use ethyl alcohol as long as there’s very little water added to it (or the flame may not ignite). You can also use methanol, but don’t bother with isopropyl alcohol as the water content is too high and it doesn’t furn as a fuel. Hope this helps!

  9. Yes – grab some of the fibers with tweezers or needle nose pliers and pull gently.

  10. Caroline Wood says:

    another question: I cannot find ethyl alcohol, can I use camp fuel or anything else in the burner? Thaks for all your help

  11. Caroline Wood says:

    is there an easy way to pull wick out of burner when it’s burned down?

  12. Pamela Szczech says:

    that is a cool one

  13. Cobalt Chloride

    Cobalt Chloride

    Cobalt chloride is harmful in the environment, so should not be flushed down the sink. Wrap it up in a sealed container like a ziploc bag and throw it in your trash.

    Here’s a simple one: you can use lemon juice to write secret messages in (use a cotton swab) and when you’re ready, you can heat the paper using an iron or an oven on the lowest temperature (take care you don’t ignite the paper!)

  14. Hope Martin says:

    Couple of questions…
    1. What do we do with the solution when we’re done? Is it safe to pour it down the drain?
    2. A little more complex question… or at least long winded… what other chemicals are there that change colors based on moisture (or maybe light)? We were thinking it would be fun to paint a picture using different chemicals that changed colors based on certain conditions. πŸ˜€

    Ooh! A third question: Can you direct me to a diagram of the water and Cobalt Chloride molecule? Thought that would be fun to show my kids.

  15. So glad you figured it out! πŸ™‚ I meant to also add into my last comment what to do if your air was too dry already, but you figured out a good way to add moisture to it. Great job!

  16. Anita Mullins says:


    After you mentioned hydrated/dehydrated, I started thinking about location and climate. We are in Fairbanks, Alaska – 100 miles south of the Arctic circle and hundreds of miles from moisture and blocked by mountains in most directions. While winter this year has been relatively mild (-20s on average at night and -10 to +5 in the daytime for months), our arctic winter air still tends to be very dry.

    I (barely) heated up a pot of water and placed a “painting” over the source of moisture. Within a few minutes the blue painting changed to light pink / purple. Removing the painting from the moisture and immediately exposing it to hair dryer heat, changed the painting to blue in a matter of seconds.

  17. The cobalt changes color when hydrated/dehydrated – think of it as an indicator for water. It should be red when you first mix it, but blue when hit with the hair dryer. It doesn’t react to acids and bases the way the red cabbage or universal indicator does, but rather with humidity. What happens when you put your index cards in the oven at its lowest setting while carefully keeping an eye on it (so it doesn’t burn)? If you live in a very humid area, something even the hair dryer isn’t enough. What kind of climate do you live in? Does it get pale at all when you freeze it?

    Here’s another idea – see if you can find one of those silica-gel packets (the ones that say ‘Do Not Eat’ that come in packages like vitamins or new shoes) and stick one in a bag with your blue painting. The silica will absorb the moisture and leave the air in the bag dry.

    The last thought is maybe a bad cobalt specimen – sometimes oddball things get mixed in with chemicals, and if your chemical reaction isn’t going the way you expected, you can contact the company you purchased it from and request another to be sent to you.

    You sound like you did a through check of everything as you went through it, so congrats on that! Science is like this – sometimes it works, and sometimes it doesn’t – and when it doesn’t is where you get to learn the most. Keep me posted!

  18. Anita Mullins says:


    Perhaps you could provide some guidance. Our “paintings” are blue all the time – regardless of freezer, hair dryer, or room temperature. For our experiment, we used distilled water (originated from a sealed unopened bottle stored in a closet for at least a year), cobalt chloride (quite a bit more than two teaspoons), multiple cotton swabs, index cards, and plain copier grade paper. We verified we created a saturated solution – we had standing cobalt chloride at the bottom of the test tube. We “painted,” with fresh cotton swabs, the mixture on 3 or 4 pieces of paper and 3 index cards. The paintings were allowed to thoroughly dry; after which, unfortunately, the results were the same for all of them – blue. The cobalt chloride is part of the kit from the Montana company you recommended. The cobalt chloride is red within the bottle.

    What could be going wrong?


  19. Hmmm… let me try again. You know how you can make chocolate out of butter, sugar, and cocoa? Well, after you make the chocolate, you can use it in other things, like chocolate chip cookies and hot chocolate, right?

    You could be picky about this and count out how many you use, like only 2 chocolate chips per cookie, or 25 per cookie, but you’d get two different cookies – one a lot more chocolately than the other.

    Molecules work the same way. You can put atoms together to make different molecules, like water, and then use different amounts of the water with other stuff. In this case, we’re using 6 ‘waters’ the same way we’d use ‘6 chocolate chips’ to build something bigger.

    How’s that?

  20. sevy keble says:

    Well…. No, not really. (I’m only in 4th grade, you know!)

  21. That means in the molecule used in this experiment, there are 6 water ‘sub-molecules’ in the chain. You can have molecules join together to make larger and larger molecules. Does that make sense?

  22. sevy keble says:

    You said that there are 6H2O particles in this. Water is H2O. Does 6H2O mean 6 water particles?
    sevy keble πŸ™‚