Shaking Solution: Difference between revisions

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== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Chemistry]]:
| Redox Reactions
|-
| Grade Range:
| [[Elementary School]], [[Middle School]], [[High School]]
|-
| Format:
| [[Hands-on]]
|}


Elementary School, Middle School, High School
This is a common demonstration for Reduction/Oxidation reactions. It is easy to prepare, easy to perform, and after preparation it can be used for several hours!


== Format ==


Stage Show, Hands-on
== Materials ==


== Materials ==
* Sodium Hydroxide
* Dextrose (Sugar)
* Water
* 500 mL Erlenmeyer flask
* Stopper for flask
* Indicator: Methylene Blue or Resazurin


    Flask and stopper
    8g Potassium Hydroxide [corrosive]
    10g Glucose (AKA dextrose)
    0.05g Methylene Blue [harmful]
    50mL Water


== Safety Precautions ==
== 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. Make sure the stopper fits tightly on the flask and that kids don't drop/break the flask. It might be a good idea to use a clear plastic pop bottle with a screw on lid. Also please check how to properly dispose of the solution.
Please read the Chemical Safety section of the [[Demonstration Safety]] page before performing this demonstration.
 
[http://www.sciencelab.com/msds.php?msdsId=9926049: Methylene Blue MSDS]
 
[http://www.sciencelab.com/msds.php?msdsId=9927230: Potassium Hydroxide MSDS]
 
== Preparation ==


    Make a solution of 0.05g o methylene blue in 50 mL of water
During preparation, wear safety goggles and gloves. During the presentation, make sure whomever is shaking the solution keeps a hand on the stopper, to prevent it from coming out.
    Add 8g of potassium hydroxide into the flask
    Add 300mL water to the flask
    Add 10g glucose to the flask
    Swirl the flask until the solids are dissolved
    Add 5mL of the previously prepared methylene blue solution. The exact quantity used is not important.  


The resultant blue solution should turn colorless after about a minute. Stopper the flask.


== Demonstration ==
== Demonstration ==


While holding the stopper securely in place, shake the flask so that air dissolves in the solution (you can let the kids try it out on their own, just make sure they wear goggles and are careful not to drop it). The color of the solution will change from clear to blue while shaking, then will go clear again after standing still for about 30 seconds. The more shaking, the longer the blue color will take to fade. Process can be repeated many times, after a while (several hours) the solution will turn yellow and the color changes won't happen anymore.
'''Preparation:'''
 
# In the Erlenmeyer flask, combine 300 mL of water with 8g of Sodium Hydroxide and 10g of Dextrose. Add the solids individually, and allow the first to dissolve fully before adding the next one.
== What to Say ==
# If your indicator is not already in a water solution, then combine 0.5-1.0 g of the indicator with 50mL of water. Stir thoroughly, store in a bottle and label it. Add 8-10 drops of the indicator solution to the Erlenmeyer flask, and then stopper the flask.  
 
# The solution will initially be blue (Methylene blue) or purple/pink (Resazurin). After you let it sit, the solution will turn clear (Methylene) or light teal (Resazurin), and it is now ready to use.
A redox reaction is one in which oxidation and reduction are taking place. Oxidation is when an atom or molecule loses electrons (or gains oxygen)
 
Reduction is when an atom or molecule gains electrons (or loses oxygen)


A good way to remember the difference is LEO says GER where LEO stands for Losing Electrons=Oxidation and GER stands for Gaining Electrons=Reduction.
'''Presentation:'''
# Show the solution to the students, and swirl the bottle gently. A very slight color change will happen. Let it sit, and after a few seconds the color will disappear!
# Ask a student to hold it and shake it. The solution will now turn colors dramatically! the more they shake it, the more pronounced the color will become, and the longer it will take for the color to dissipate.
# Ask the students why it changes colors. What is happening when we shake it? Is there more than one thing going on here?


So what happens when we shake the solution? --- We dissolve air (and therefore oxygen!) into the solution. We just learned that when a molecule gains oxygen it is oxidized. So when we shake the solution, the glucose is oxidized.


An indicator is something that can be used to tell us what is going on in a solution. Methylene blue is a redox indicator that is colorless when under reducing conditions, and turns blue under oxidizing conditions. So when we shake the solution, we oxidize the glucose and the methylene blue turns blue!
== Why This Works ==


What happens when we let the solution sit for a while? The solution is reduced (loses oxygen) and the methylene blue returns to a colorless state.
This demonstration works because it is a '''''Redox Reaction'''''. Redox stands for Reduction/Oxidation, two types of reactions that, typically, involve an exchange of electron charges, usually by use of Oxygen atoms. Reduction is when a molecule loses an Oxygen, and gains electrons. Oxidation is when a molecule gains an Oxygen, and loses electrons. A helpful way to remember this is with this phrase: "'''LEO''' says '''GER'''". The letters in '''LEO''' stand for '''L'''oss '''E'''quals '''O'''xidation, and '''GER''' stands for '''G'''ain '''E'''quals '''R'''eduction.


What happens if we shake the flask for a very long time? The time that the flask is shaken is directly proportional to the amount of time that it will take for the blue color to fade. So the longer you shake the flask, the longer it will take to return to it original (lack of) color. This is because the longer you shake the solution the more oxygen is dissolved, and the solution remains oxidized longer.  
Remember: There is air all around us, including inside of the flask, and part of that air is Oxygen. So when the flask is shaken, some of that Oxygen dissolves into the solution. It bonds to the dextrose, which causes it to be oxidized. The indicator can tell when glucose is oxidized, and when that happens the indicator changes color.  


== Why It Is ==
'''Full Explanation'''


Methylene Blue is a redox indicator that is colorless under reducing conditions and blue when oxidized. The glucose in the solution causes the methylene blue to initially be colorless. When the solution is shaken, oxygen dissolves into it. This oxidizes the glucose, which gives the methylene blue its blue color, indicating the oxidative conditions. When the oxygen is no longer dissolved in the solution (after you let it sit for a while), the glucose returns to its reduced state and the solution loses its blue color. The longer you shake the solution, the longer it will take to return to its colorless state because more oxygen is initially dissolved.
Redox stands for Reduction/Oxidation. Reduction is when electrons are gained, usually by the loss of an Oxygen. Oxidation is when electrons are loss, usually by the gain of an Oxygen. A helpful way to remember this is with this phrase: "'''LEO''' says '''GER'''". The letters in '''LEO''' stand for '''L'''oss '''E'''quals '''O'''xidation, and '''GER''' stands for '''G'''ain '''E'''quals '''R'''eduction.


Oxidation refers to the loss of electrons/hydrogen or the gain of oxygen/increase in oxidation state by a molecule, atom, or ion.
In this experiment, we are seeing a color change when the oxidation of Methylene Blue takes place.  


Reduction refers to the gain of electrons/hydrogen or the loss of oxygen/decrease in oxidation state by a molecule, atom, or ion.
'''''INSERT FULL EXPLANATION HERE'''''


The reaction:
'''''FULL EXPLANATION IS QUITE COMPLICATED'''''


HOCH2(CHOH)4CHO + 3 OH - → HOCH2(CHOH)4CO2 + 2 H2O + 2 e –
→


== Real Life Examples ==
== Additional Information ==


In the dairy industry the dye reduction test using methylene blue is used to determine whether milk is classified as “excellent”, “good”, “fair”, or “poor” based on the rate at which the solution turns colorless. The faster the methylene returns to its colorless state, the lower the rating. This is because the bacteria that sometimes live in milk use oxygen as fuel. The more bacteria in the milk, the less oxygen there is, and so the oxidized (blue) state of the methylene blue fades more quickly.
* Redox Reactions are all around us! Combustion is a redox reaction, and rust on metals is one as well!
* Methylene Blue is used to check the quality of milk produced. After added to some milk, the rate that it turns blue determines what rating the milk gets. A slow change is good, and a fast change is poor.
* This demonstration is a part of the [[Chemistry Show]]!

Revision as of 22:40, 21 October 2015

Chemistry: Redox Reactions
Grade Range: Elementary School, Middle School, High School
Format: Hands-on

This is a common demonstration for Reduction/Oxidation reactions. It is easy to prepare, easy to perform, and after preparation it can be used for several hours!


Materials

  • Sodium Hydroxide
  • Dextrose (Sugar)
  • Water
  • 500 mL Erlenmeyer flask
  • Stopper for flask
  • Indicator: Methylene Blue or Resazurin


Safety Precautions

Please read the Chemical Safety section of the Demonstration Safety page before performing this demonstration.

During preparation, wear safety goggles and gloves. During the presentation, make sure whomever is shaking the solution keeps a hand on the stopper, to prevent it from coming out.


Demonstration

Preparation:

  1. In the Erlenmeyer flask, combine 300 mL of water with 8g of Sodium Hydroxide and 10g of Dextrose. Add the solids individually, and allow the first to dissolve fully before adding the next one.
  2. If your indicator is not already in a water solution, then combine 0.5-1.0 g of the indicator with 50mL of water. Stir thoroughly, store in a bottle and label it. Add 8-10 drops of the indicator solution to the Erlenmeyer flask, and then stopper the flask.
  3. The solution will initially be blue (Methylene blue) or purple/pink (Resazurin). After you let it sit, the solution will turn clear (Methylene) or light teal (Resazurin), and it is now ready to use.

Presentation:

  1. Show the solution to the students, and swirl the bottle gently. A very slight color change will happen. Let it sit, and after a few seconds the color will disappear!
  2. Ask a student to hold it and shake it. The solution will now turn colors dramatically! the more they shake it, the more pronounced the color will become, and the longer it will take for the color to dissipate.
  3. Ask the students why it changes colors. What is happening when we shake it? Is there more than one thing going on here?


Why This Works

This demonstration works because it is a Redox Reaction. Redox stands for Reduction/Oxidation, two types of reactions that, typically, involve an exchange of electron charges, usually by use of Oxygen atoms. Reduction is when a molecule loses an Oxygen, and gains electrons. Oxidation is when a molecule gains an Oxygen, and loses electrons. A helpful way to remember this is with this phrase: "LEO says GER". The letters in LEO stand for Loss Equals Oxidation, and GER stands for Gain Equals Reduction.

Remember: There is air all around us, including inside of the flask, and part of that air is Oxygen. So when the flask is shaken, some of that Oxygen dissolves into the solution. It bonds to the dextrose, which causes it to be oxidized. The indicator can tell when glucose is oxidized, and when that happens the indicator changes color.

Full Explanation

Redox stands for Reduction/Oxidation. Reduction is when electrons are gained, usually by the loss of an Oxygen. Oxidation is when electrons are loss, usually by the gain of an Oxygen. A helpful way to remember this is with this phrase: "LEO says GER". The letters in LEO stand for Loss Equals Oxidation, and GER stands for Gain Equals Reduction.

In this experiment, we are seeing a color change when the oxidation of Methylene Blue takes place.

INSERT FULL EXPLANATION HERE

FULL EXPLANATION IS QUITE COMPLICATED

→

Additional Information

  • Redox Reactions are all around us! Combustion is a redox reaction, and rust on metals is one as well!
  • Methylene Blue is used to check the quality of milk produced. After added to some milk, the rate that it turns blue determines what rating the milk gets. A slow change is good, and a fast change is poor.
  • This demonstration is a part of the Chemistry Show!
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