Calcium Carbonate -> Calcium Oxide, but only getting Hydroxide. Ideas?

  1. I was trying to calcine some CaCO3 (Calcium Carbonate), but ended up with Calcium Hydroxide.

    To test if I had Calcium Carbonate I added it to some vinegar, no gas was produced. I then mixed in a small amount of the powder with a large amount of water and passed CO2 through it, and it became a milky white which led me to believe I have Calcium Hydroxide. I also tried added the final powder to water, which did not heat up.

    I heated up my CaCO3 in a laboratory furnace (Electric) at roughly 920°C for 30 minutes which left me with my current product.

    Do I need to have a nitrogen/argon gas purge of some sort??

    Any ideas are appreciated! Thanks!
    Last edited: Sep 14, 2013
  2. jcsd
  3. Borek

    Staff: Mentor

    You are doing strange tests and drawing strange conclusions.

    Some gas should be produced, so this test - if anything - shows you didn't have a calcium carbonate. I wonder if you didn't mean you were testing for oxide?

    Sorry, no idea what you are trying to test for. Assuming the powder was CaO, after mixing it with water it became Ca(OH)2. It doesn't mean your powder WAS calcium hydroxide.

    How much powder, how much water?
  4. I was testing with vinegar to verify a change had taken place, and that it was heated long enough. This would only show that I did not have a carbonate.

    I suppose you're right that both CaO, and Ca(OH)2 would form a milky white mixture, but when I added the powder to water (just enough water to cover the powder ~20-50ml) there was absolutely no change in temperature as measured with an IR thermometer and by touch.

    20-50ml, just enough to cover the powder.
  5. Borek

    Staff: Mentor

    Have you checked that the carbonate before roasting was reacting with the acid?

    How much powder? A pinch, or so much that the water was only a thin layer on the surface?
  6. AlephZero

    AlephZero 7,248
    Science Advisor
    Homework Helper

    I wonder if you got the CaCO3 hot enough. Wikipedia gives the minimum temperature as 825C.

    You certainly don't need a gas purge. Cement making isn't "high tech" chemistry! Heating a 10mm diameter limestone chip directly with a roaring bunsen burner flame for a couple of minutes should work. But a bunsen flame is about 1500C, not 920C.
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