Chlorine The Bacteria Killer
Age
Elementary School, Middle School
Format
Hands-on
Materials
Chlorine Bleach Sugar yeast test tubes (min 4) party balloons (min 4) water heater 2 beakers (each large enough to hold 2 test tubes) 1 beaker (for diluted bleach) 3 large tubs (1 for warm water, 1 for rinse, 1 for waste materials) 2 measuring cups (1 for sugar, 1 for yeast) 2 10 mL graduated cylinders (1 for chlorine bleach, 1 for warm water)
Safety Precautions
Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. Add safety information-Chlorine bleach is potentially dangerous if it comes into contact with the eyes, skin, or is swallowed or inhaled.
Chlorine Bleach(<5% Sodium Hypochlorite) MSDS
- To protect yourself from these hazards wear safety goggles, gloves, dilute the bleach with water to a level were the fumes are no longer overpowering, and keep the bottle capped to prevent spills.
- To protect others, keep a watchful eye on the bleach or keep it in a spot where children or childish people cannot get to it. Be careful not to spill onto others.
- Let no one consume any part of the demo!!!
- If ANY chlorine bleach gets into eyes: Flush eyes gently with water for 15 minutes while holding the eyelids apart.
- If any undiluted bleach comes into contact with skin: Flush skin with water for 15 minutes, while removing contaminated clothing.
- If ANY chlorine bleach is swallowed: seek immediate medical attention. (DO NOT INDUCE VOMITING). Immediately rinse the mouth out with water or milk. Do not leave the individual unattended.
- To prevent symptoms caused by Inhalation dilute the bleach and move effected individuals to areas with fresh air.
Demonstrators should wear goggles and lab coats, and the ST general safety box should be available to them.
Preparation
1) Dilute bleach until is it useable. (smell is no longer overpowering)
2)Inflate and deflate balloons to stretch latex.
3)Fill a beaker with warm water.
4)Label respective balloon/test tube “Control” and “Chlorine”.
NOTE: these are the same steps done during the demo these first tubes made are just examples of the final product.
Demonstration
Before the demo
1) Half fill two test tubes with warm water
2) Add ¼ teaspoon yeast with ¼ sugar to each of the two test tube.
3) To one of the two test tubes add ½ teaspoon of diluted chlorine bleach.
4) Set these test tubes aside for at least 15 minutes for later use.
5) Keep track of which tube has chlorine bleach and which is the control tube.
During the demo
1) Repeat steps 1-3 while explaining what you are doing
2) Instead of waiting for these new text tubes to fill the balloons pull out prepared test tubes, and explain that the same thing was done to them, just earlier.
What to Say
1) Asking audience “Have any of you ever swam in a swimming pool?”
<After positive response of “yes” to 1)>
2)“well then, do you know that particular smell that a pool has?”
<after negative response to 1) or positive response to 2)>
2a) “well have you ever been to a lake?”
<after response>
2b) “well, lakes and pools are very different. Pools have pool cleaner in them, that’s what causes them to smell. Lakes have stuff living in them like fish, bacteria, and seaweed.”
<continue to 3>
<After positive response of “yes”to 2)>
3)“That smell in pools is caused by a chemical called Chlorine”
points to picture of periodic table**
“Chlorine is used as a cleaning agent in pools and many other things that kills bacteria and germs that can get you sick.”
Asking audience,“Do you guys know what bacteria is?”
<positive response of “yes” or negative response of “no”>
4)”(yeah that’s right), “they’re little tiny organisms.”
Asking audience, “Have any of you heard of yeast?”
<positive response “yes” or negative response “no>
5)”(It’s used a lot in baking, but more importantly) yeast is alive!!!”
“that’s right yeast is alive, in fact yeast is a little tiny fungus. We’re going to use it to represent bacteria and germs in a swimming pool.”
Place ¼ tsp yeast into test tube**
“Now we need to put water into our pool”
Fill each test tube ½ full of warm water**
“But we don’t want our little yeast to starve do we?! I know we’ll give it sugar.”
“So right now we’ve got two test tubes filled with water and well fed yeast.”
“This represents a swimming pool with bacteria and germs that are very happy and well fed.”
“Let’s see what happens when we put Chlorine into the pool”
add ½ teaspoon diluted Chlorine Bleach into 1 test tube.**
“But how will we know if this works? What do all living organisms do when they are alive?
<wait for answers poop, eat, move, ect… until breath.>
say “They do this really AWESOME thing RESPIRATION where they dispel carbon dioxide”
“What we’re going to use to measure whether or not out yeast is breathing is out carbon dioxide, is attach a balloon on top of the test tube, so when the yeast exhales it will fill up the balloon!!!”
attach balloons to test tubes**
“But we’d have to wait a pretty long time for the yeast to fill up this balloon, so earlier I prepared the exact same experiment, so you wouldn’t have to wait so long.”
pull out prepared test tubes**
“Can you tell which one has the chlorine in it?”
“Do you think the balloon the balloon that is inflated has live yeast in it or the balloon that is deflated?”
“the the inflated balloon actually belongs to the one with out chlorine and live yeast.”
“since we put yeast and sugar in both of the test tubes we can tell that the chlorine kills the yeast and stops its respiration, because the tube that I put chlorine in has a deflated balloon”
Why It Is
Active dry yeast is a fungus in the dormant stage. Yeast cells produce carbon dioxide when they metabolize sugar. The test tube with chlorine show have less carbon dioxide produced in it’s balloon because the chlorine should have killed most of the yeast. When Chlorine is added to water a reaction occurs splitting it into hypochlorous acid (HOCl) and hypochlorite ions (-OCl). Both are strong oxidizing agents that kill microbes by destroying their cell walls and key enzymes in the cell used for metabolism.
Real Life Examples
Pool, lake, laundry detergent