The Naked Scientists

The Naked Scientists Forum

Author Topic: Please help! Clear liquid + Clear liquid = one liquid turns blue other clear  (Read 12375 times)

Offline Demi

  • First timers
  • *
  • Posts: 3
    • View Profile
Hi,

I am doing a presentation for late elementary/middle school age children about microbiology.  I know that micro is kind of a sloooow field for experiments because things need to grow so I was thinking some kind of demonstration for the kids that can simulate how fast bacteria/virus can spread amongst eachother.

Hear me out:  I did something similar in my chemistry class and don't remember the actual substances.

I was thinking of having the kiddos each have a small cup of "water" or some clear liquid that's odorless.  I would first tell them that some of them are sick with the flu and some are healthy, we will then have each of them go around and shake hands which would be simulated by mixing their liquids with 2-3 friends, not knowing who has the special liquids. 

At the end of the experiment, I would put a drop of something in each cup, "flu test", and those that turned pink/blue/red or some color have the flu while others that stayed clear remained healthy.  Just to show the kiddos how easily it is to spread the virus.  I would then reveal who were the original "flu" carriers.  This can help me present how important it is to prevent the spread of cold and flu germs by washing hands.. yadda yadda.  Please help me.  I don't know what two clear liquids I can mix to make a nice bold color.

Thanks in advance,

Demi


 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8128
  • Thanked: 53 times
    • View Profile
Given a cup of some liquid one of the little darlings may drink the contents so it had better be non-toxic,
(and non-irritant).

Glucose dissolved in water would be colourless and edible.

Urinalysis dipstick tests for glucose (for diabetes) undergo a colour change and could be used to quickly (30 seconds) show the presence of glucose (not sucrose) in the liquid in a cup ...



Their sensitivity is 100-mg/dl : the concentration of glucose in the dilute cups would have to be higher than that to produce the colour change. 

http://www.mdk12.org/instruction/curriculum/science/safety/chemicals.html
« Last Edit: 29/02/2012 00:03:44 by RD »
 

Offline Demi

  • First timers
  • *
  • Posts: 3
    • View Profile
Thanks for your response!  So the strip will change color, not the liquid?  That's a good one, but I'm really looking for a color changing liquid (for the visual effect).  Some of the younger kids may not get the point if it's on a strip.  Not sure if it's going to be possible.  I'd like for the actual liquid they are holding in the cup to be non-toxic, but the indicator can be whatever because I will control the dropping of that into the cup and they will not be able to have the cup back after i've dropped the indicator. 

I was thinking something like with baking soda and water making it slightly basic or salt water.  Not sure if there are indicators for salt water or slightly acidic water (as with lemon juice) or like sprite.  I'm not a chemist so please excuse me if I've made a faux pas in chemicals.  Please keep giving me good ideas.
 

Offline Demi

  • First timers
  • *
  • Posts: 3
    • View Profile
I wanted to also add that they won't have a whole bunch of liquid in the cup.  I was thinking like 2-3 oz. of liquid for each student in one of those bathroom cups (people use for mouthwash).  That will cut down on any serious risk lets say if the liquid was a mixture of baking soda and water or soda or lemon juice and water or whatever and also so the active liquid doesn't get diluted too much so that the indicator doesn't work.
 

Offline RajNSF

  • Jr. Member
  • **
  • Posts: 12
    • View Profile
You can use dilute sodium hydroxide solution and phenolphthalein. Both are colorless unless u mix them. xx(
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8128
  • Thanked: 53 times
    • View Profile
You can use dilute sodium hydroxide solution

Giving primary school children mouthwash cups of caustic soda is not a good idea, (clue in the title).
« Last Edit: 04/03/2012 07:40:34 by RD »
 

Offline RajNSF

  • Jr. Member
  • **
  • Posts: 12
    • View Profile
Ah yah that's why I put this --->  xx(
 

Offline Lmnre

  • Sr. Member
  • ****
  • Posts: 178
    • View Profile
I think you have found an excellent experiment.

Whatever substances you choose, you might want to try more than one experiment with the kids.

For example, Experiment #1 begins with only 1 kid in the class of 20 originally "infected". Experiment #2 begins with 3 kids "originally infected". Etc. So, this shows probability of infection as a function of original percentage infected.

Or, begin with X kids "infected". Experiment #1 has them "shake hands" with 2 other kids. Experiment #2 with 5 other kids. Etc. This can simulate both the flu and STDs. This shows probability of infection based on number of encounters.
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8128
  • Thanked: 53 times
    • View Profile
I think you have found an excellent experiment.

The demonstration is not pedagogically sound : the chemicals do not multiply like micro-organisms, the chemical concentration becomes increasingly dilute with each transmission. Kiddies could get the wrong idea that that is also true of infection.

IMO a demo which could have health and safety risks, and which does not properly illustrate the concept its a non-starter.
 

Offline Lmnre

  • Sr. Member
  • ****
  • Posts: 178
    • View Profile
All we're looking for is a substance in a liquid that is undetectable to the unaided eye/nose, but produces a quick and dramatic indication by other means.

Perhaps a version of the Iodine Clock Reaction would work. If the dangerous components could somehow be introduced only at the end during the "testing phase".

Here's an experiment with over-the-counter components. Perhaps the kids could play with cups of water with Vitamin C in them. The "non-infected" cups would contain water, perhaps disguised with a little food coloring (or maybe all cups need a little food coloring) to make all of them uniform in color.
« Last Edit: 10/03/2012 21:01:04 by Lmnre »
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums