Shaking Solution - Revision history

imported>Stwikiadmin at 18:14, 26 September 2016

2016-09-26T18:14:06Z

imported>Stwikiadmin: /* Why This Works */

2015-10-22T17:28:01Z

Why This Works

← Older revision		Revision as of 17:28, 22 October 2015
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	== Why This Works ==		== 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 '''L'''oss '''E'''quals '''O'''xidation, and '''GER''' stands for '''G'''ain '''E'''quals '''R'''eduction.		===Short Explanation===

	~~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~~.		This demonstration works because it is a '''''Redox Reaction'''''. Redox stands for Reduction/Oxidation, which are reactions that happen due to an exchange of electrons. Reduction is when a molecule gains electrons, and Oxidation is when a molecule 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.

	~~'''Full Explanation'''~~		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 will dissolve into the solution. The Oxygen will oxidize the indicator, and removes some of the electrons. This is what makes it change colors! Then, the glucose in the solution will reduce the indicator, and give it some electrons. This is what makes it turn back. Since there is so much glucose in the solution and very little indicator, this can happen a lot, and can be repeated for several hours!

	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.

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

	'''''~~INSERT FULL EXPLANATION HERE~~'''''		Redox stands for Reduction/Oxidation. Reduction is when electrons are gained, usually by the loss of an Oxygen. Oxidation is when electrons are lost, 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.

	''''~~'FULL EXPLANATION IS QUITE COMPLICATED'''''~~		In this experiment, we are seeing a color change when the oxidation of the indicator takes place. For this to happen, however, we need to first have our indicator be reduced. What is often missed during this demonstration is that, when we shake the solution, we are effectively ''reversing'' a step of the reaction that took place. This is why it will always go back to clear at the end, since the reaction will then go forward.

	→		The initial reaction is between the Sodium Hydroxide and Dextrose:

			C<sub>6</sub>H<sub>12</sub>O<sub>6(aq)</sub> '''+''' 2NaOH<sub>(aq)</sub> '''⇒''' C<sub>6</sub>H<sub>12</sub>O<sub>7(aq)</sub> '''+''' 2Na<sup>+</sup><sub>(aq)</sub> '''+''' H<sub>2</sub>O<sub>(l)</sub> '''+''' 2e<sup>-</sup>

			This reaction turns the Dextrose into Gluconic Acid, and frees two electrons. This means it was Oxidized, since it lost electrons, and also happened to gain an Oxygen. Gluconic Acid is a weak acid, so although it does react with the alkali solution it is in, it does so slowly. This will produce a free Hydrogen, and it will become a Gluconate ion:

			C<sub>6</sub>H<sub>12</sub>O<sub>7(aq)</sub> '''⇒''' C<sub>6</sub>H<sub>11</sub>O<sub>7</sub><sup>-</sup><sub>(aq)</sub> '''+''' H<sup>+</sup><sub>(aq)</sub>

			The Hydrogen, combined with the two extra electrons, is what changes the color of the solution. The indicators we use is either Methylene Blue or Resazurin, both of which are redox indicators. This means that they will have a color shift when a Redox reaction happens. When we first add them in, they are reduced:

			'''Methylene Blue:''' C<sub>16</sub>H<sub>18</sub>N<sub>3</sub>S<sup>+</sup><sub>(aq)</sub> (Blue) '''+''' H<sup>+</sup><sub>(aq)</sub> '''+''' 2e<sup>-</sup> '''⇒''' C<sub>16</sub>H<sub>19</sub>N<sub>3</sub>S<sub>(aq)</sub> (Colorless)

			'''Resazurin:''' C<sub>12</sub>H<sub>7</sub>NO<sub>4</sub><sup>-</sup><sub>(aq)</sub> (Purple/Pink) '''+''' 2H<sup>+</sup><sub>(aq)</sub> '''+'''e<sup>-</sup> '''⇒''' C<sub>12</sub>H<sub>7</sub>NO<sub>3(aq)</sub> (Teal) '''+''' H<sub>2</sub>O<sub>(l)</sub>

			After the initial reduction, The solutions are ready for presenting. When you shake the solution, Oxygen will be dissolved into it. The dissolved Oxygen will react with the indicators, Oxidizing them and causing a color change:

			'''Methylene Blue:''' 2C<sub>16</sub>H<sub>19</sub>N<sub>3</sub>S<sub>(aq)</sub> (Colorless) '''+''' O<sup>2-</sup><sub>(aq)</sub> '''⇒''' 2C<sub>16</sub>H<sub>18</sub>N<sub>3</sub>S<sup>+</sup><sub>(aq)</sub> (Blue) '''+''' H<sub>2</sub>O<sub>(l)</sub>

			'''Resazurin:''' C<sub>12</sub>H<sub>7</sub>NO<sub>3(aq)</sub> (Teal) '''+''' O<sup>2-</sup><sub>(aq)</sub> '''⇒''' C<sub>12</sub>H<sub>7</sub>NO<sub>4(aq)</sub> (Purple/Pink) '''+''' 2e<sup>-</sup>

			This will cause the Gluconic Acid to release more Hydrogen into the solution, and return the indicators to their reduced states. As long as there is enough Gluconic acid in solution, and so long as there are some extra electrons in solution, then you will be able to shake the solution and cause the color change! Due to the amount of indicator being so low compared to the other reactants, This reaction is able to happen a lot, and for a long while.

			After a few hours, the solution will change color slightly and stop working. It stops working because of the lack of free electrons and Hydrogen to make the reverse reaction happen. The color change happens because, after expending all of the extra Hydrogen and electrons, the indicators will bond with some of the other ions in solution, such as the Gluconate ions and the Sodium ions, and become unable to do their proper color changes.

	== Additional Information ==		== Additional Information ==

imported>Stwikiadmin at 22:40, 21 October 2015

2015-10-21T22:40:21Z

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imported>Stwikiadmin: moved Blue Shaking Solution to Shaking Solution

2015-10-21T15:55:49Z

moved Blue Shaking Solution to Shaking Solution

← Older revision		Revision as of 15:55, 21 October 2015
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imported>Stwikiadmin at 14:38, 11 September 2013

2013-09-11T14:38:43Z

← Older revision		Revision as of 14:38, 11 September 2013
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	[http://www.sciencelab.com/msds.php?msdsId=9926049: Methylene Blue MSDS]		[http://www.sciencelab.com/msds.php?msdsId=9926049: Methylene Blue MSDS]

	[http://www.sciencelab.com/msds.php?msdsId=9927230: Potassium Hydroxide MSDS]		[http://www.sciencelab.com/msds.php?msdsId=9927230: Potassium Hydroxide MSDS]

imported>Stwikiadmin: Created page with "== Age == Elementary School, Middle School, High School == Format == Stage Show, Hands-on == Materials == Flask and stopper 8g Potassium Hydroxide [corrosive] 10..."

2013-09-11T14:38:34Z

Created page with "== Age == Elementary School, Middle School, High School == Format == Stage Show, Hands-on == Materials == Flask and stopper 8g Potassium Hydroxide [corrosive] 10..."

New page

== Age ==

Elementary School, Middle School, High School

== Format ==

Stage Show, Hands-on

== Materials ==

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

[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
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 ==

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.

== What to Say ==

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.

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!

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.

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.

== Why It Is ==

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.

Oxidation refers to the loss of electrons/hydrogen or the gain of oxygen/increase in oxidation state by a molecule, atom, or ion.

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

The reaction:

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

== Real Life Examples ==

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.