Ask Experts Questions for FREE Help !
    jwertzski's Avatar
    jwertzski Posts: 1, Reputation: 1
    New Member

    Nov 17, 2005, 08:18 PM
    Chemical that knows how humid it is.
    Many years ago while attending a state fair in the mid-west one vendor would give away a one inch by three inch piece of paper that had the thickness like a manila file folder. This was impregnated with a chemical on a spot about the size of a dime. It had a pink color to it and when the humidity increased it would change to blue. Or maybe it was the other way around. When the humidity decreased, it would revert back to the original color. What chemical would that have been?
    kp2171's Avatar
    kp2171 Posts: 5,318, Reputation: 1612
    Uber Member

    Nov 20, 2005, 07:19 PM
    Mix of cobalt chloride along with other salts.

    The cobalt chloride changes color depending on the moisture level. I don't know, but I imagine this is from waters coordinating with the salt... other salts will coordinate waters as well, like epsom salt (MgSO4) but epsom salt looks white when coordinated with water or dehydrated. Cobalt chloride shows a color shift.

    Added salts like NaCl or CaCl2 have nothing to do with the color other than they absorb moisture.

    Here's a link. You may have problems getting cobalt chloride unless you buy from a chemical supplier or know someone who works in a chemical lab.

    Or you can buy paper already manufactured at :

    Haven't used either the recipe or the product, but I'd do some more searches for cobalt chloride and see what you get.

    Chemists use a brand called drierite to dry air supplies to chemical reactions and they sometimes use this indicator to show the chemist when it is "spent".. and some moisture sensitive instruments utilize the same kind of discs with indicator... shows when the dessicants are spent and need replaced.

Not your question? Ask your question View similar questions


Question Tools Search this Question
Search this Question:

Advanced Search

Check out some similar questions!

Chemical-physical changes [ 3 Answers ]

What is the difference of a physical and a chemical change?

Drawing chemical structures? [ 1 Answers ]

Please can you tell me how I go about drawing structures for chemicals. I'm presently doing physics and don't know anything about chemistry structures. I've been given the task to draw the structure for the following compound: Pyridinium, 4- ethenyl]-1-(sulfobutyl)-, inner salt. Any...

[HELP]gr11 chemistry - predicting chemical reactions and balancing chemical equations [ 5 Answers ]

hey can nebody help me with my chemistry hmwk? i dun really get it... :confused: thanks! For each of the following reactions, determine what the products of each reaction will be. When you have predicted the products, balance the equation and use a table of solubility products to...

View more questions Search