Research: Redox Reactions

Photosynthesis

redox reaction:

6CO2+6H2O+Light→C6H12O6+6O2

Photo-sythesis

The redox reaction happening in here is the water (H2O) is losing electrons (reduced) to then produce oxygen, and then Carbon Dioxide (CO2) is being reduced which then turns it into glucose. There are two stages, the light dependent and light independent reactions. In the light dependent reaction, light energy is absorbed by chlorophyll. This energy is then used to split water molecules to oxygen and hydrogen ions, releasing electrons in the process.

Bleach

redox reaction:

ClO- + H2O → HOCl + OH-

Bleach

Disenfecting water with bleach is entirely possible, it can be used to kill bacteria and other microorganisms. It produces hypochlorous acid (HOCl) which is a very strong disinefectant. This is a redox reaction becasue the hypochlorite ion is redduced to hypochlourous acide, while the organic matter is oxidized.

Rust

redox reaction:

4Fe2+ + O2 → 4Fe3+ + 2O2-

Rust

Rusting of iron is considered as a redox reaction because the iron is losing electrons (oxidized) and the oxygen gains electrons (reduced), when there’s water and other electrolytes such as salt, it can speed up the rusting process by facilitating the transfer of electrons between the iron and oxygen

Combustion of Octane

redox reaction:

2C8H18(l)+25O2(g)→16CO2(g)+18H2O(g)

The octane (C8H18) is being oxidized by oxygen (O2) to then produce carbon dioxide (CO2) and water (H2O). The carbon in octane has a 2+ oxidation state, and the oxygen molecule has a 0 oxidation state. After the reaction oxygen is reduced to water while carbon is oxidized to form carbon dioxide. Why doesn’t a bottle of gasoline left open, combust? Because you must overcome the activation energy of the reaction. Meaning you must put in energy such as an electrical spark. It can also come from other sources such as energy from the sun, matches, friction, etc.

Octane

(and yes the image is in french)

Photography

Photography

Cameras (specifically film cameras) are redox reactions. The process begins when the camera shutter opens and allows light to hit the film containing a light sensitive silver-bromide. The light’s energy oxidizes the bromide ions into elemental bromine. The silver ions will then be reduced into metallic silver atoms. Silver atoms do not form in the areas that have not been touched by light. Grains will activate more frequently the brighter the light. They will then gradually transform into the darker areas after they have been developed. The redox reaction equation is:

2Ag+ + 2Br- -> 2Ag + Br2

Breathalyzer

Breathalyzer

Redox reactions occur in breathalyzer as potassium dichromate is reduced into chromium sulfate when it loses an oxygen atom as it comes into contact with ethanol. The ethanol is oxidized into acetic acid as it takes the oxygen atom from potassium dichromate. The role of the sulfuric acid is to transfer the ethanol into the test solution from your exhaled air. It also allows to stabilize the acidic conditions.

Browning of Fruits and Vegetables (Enzymatic Browning)

Food

Browning

This occurrence is a redox reaction as the cells of the fruit are broken down when its surface has been cut and exposed to oxygen. In a more descriptive way, the chloroplasts and vacuoles release two things when it is sliced and exposed to air: polyphenol oxidase enzyme and phenols. Polyphenol oxidase enzymes produce quinones as they are oxidizing the phenols. This is specifically called an aerobic oxidation reaction, a reaction in which oxygen and phenols are chemically bonded together. Enzymatic does not occur in all fruits and vegetables as well. As you know, when oxidation occurs, it reduction must also occur as both go hand in hand.

What are they?

What are they?

An antioxidant is like a superhero molecule that helps protect our cells from harm. When our cells undergo oxidation reactions, they can produce harmful free radicals that cause damage to our bodies. But antioxidants come to the rescue by slowing down these reactions and removing free radicals before they can cause too much harm. It can be visualized as a game of tag, antioxidants tag the free radicals to stop them from causing a chain reaction of damage. Antioxidants themselves could also by becoming oxidized to prevent further reactions. Common antioxidants are found in foods like fruits and vegetables, and they play a crucial role in keeping our bodies healthy. Antioxidants were actually also used during ancient times, used to preserve food. The 1990s was the very recent time it has been brought into attention. Studies have apparently shown that individuals who did not consume fruits and vegetables rich in antioxidant were more likely develop chronic conditions. People who consumed plenty on the other hand, had a lower chance.

How do they work?

How do they work?

Antioxidants are special chemicals that come in many different shapes and sizes. There are two main groups of antioxidants, one that dissolves in water and one that dissolves in lipids (some sort of fatty acids) The lipid-soluble antioxidants help protect the cell membranes from being damaged by the process called lipid peroxidation. While on the other hand the water soluble antioxidants work to fight the harmful substances in the plasma and cytoplasm of cells. There are multiple ways that these substances can be received, it can be made by our bodies or instead be obtained through the food we eat. There are various concentrations throughout our bodies , with them mostly being located inside cells. Antioxidants would also repair any damage they themselves have caused, basically acting like a personal protective shield for our own body to keep ourselves healthy.

Redox Reaction?

So what are the redox reactions? Antioxidants would either donate electrons (reducing agent) or accept electrons(oxidizing agent). For example, looking at Vitamin C which is an antioxidant that can donate electrons to Free radicals, which basically reduces them and stops any further damage. It can be shown in this way: Vitamin C (reduced form) + Free Radical → Vitamin C (oxidized form) Free Radical (reduced form). Antioxidants could also be used to slow down many diseases such as Alzheimer’s, Parkinson’s, some pathologies of diabetes, rheumatoid arthritis and any other diseases that are caused by neurodegeneration.

Redox Reaction?

Why is it Considered a Redox Reaction?

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If we view cellular respiration in a chemist’s perspective, losing electrons would be oxidation and gaining electrons would be reduction. In a biologist’s perspective, losing hydrogen atoms atoms would be oxidation and gaining hydrogen electrons atoms would be reduction (We are using the biologist’s perspective as a proxy). On the periodic table, oxygen is more to the left than carbon, meaning that it has more electronegativity. This makes sense with the chemical equation for cellular respiration C6H12O6 + O2→ CO2 + H2O, as the hydrogen is bonded with oxygen rather than carbon. Naturally, the element with the lower electronegativity will be a strong reducing agent, and therefore will most likely give up its electrons. Likewise, the element with the higher electronegativity will be a strong oxidizing agent, and will therefore most likely gain the electrons. In cellular respiration, the glucose is oxidized into carbon dioxide while the oxygen is reduced into water (See the next slide to view the actual redox reactions involved).

Additionally, the electron carriers (NAD+ and FAD) in cellular respiration are also redox reactions. In a way, they ‘pick up electrons’ and drop electrons’ off. As this process occurs, hydrogen is also gained and lost. If we depict this reaction as half reactions, it would look like:

Pick up : NAD+ + 2e- + 2H+ -> NADH + H+

FAD + 2e- + 2H+ -> FADH2

Drop off : NADH -> NAD+ + 2e- + H+

FADH2 -> FAD + 2e- + 2H+

The Actual Redox Reaction Involved:

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Brief History + Impact on Society

In 1860, Louis Pasteur discovered that fermentation was because of microorganisms, in turn, this initiated the explanation of glycolysis. In 1905, scientists discovered that fermentation needed two of these components: zymase and cozymase. They also discovered that inorganic phosphate was needed as well. The complete process was learned decades later in 1940. When Albert Szent-Gyoryi was able to explain the reactions that occurred during this metabolic process, Hans Adolf Krebs referenced his work and was able to create the complete Krebs cycle. The ETC was discovered by Albert Lehninger in 1961. Lehninger proposed that this phase contained four membrane bound complexes and two mobile electron carriers.

Cellular respiration has a great hold on society as photosynthesis and cellular respiration have a connection with each other. In fact, the chemical equation of cellular respiration is much closer to photosynthesis than you think: 6CO2 + 6H20 -> C6H12O6 + 6O2. As we can see here, their chemical equations are the exact opposite! Plants can not eat food like we do, so instead they must make glucose first. That glucose is converted back into carbon dioxide during cellular respiration while the water on the other hand, is broken down to form oxygen. In turn, oxygen is bonded with hydrogen to form water. Not only these two processes are impactful in living organisms, but impactful to the biosphere as well. The carbon dioxide produced in cellular respiration is released then is taken out of our atmosphere during photosynthesis. These two processes go hand in hand and we’d definitely die if it never occurred!

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References + Resources

-https://www.uspharmacist.com/article/an-overview-of-antioxidants#:~:text=An%20antioxidant%2C%20or%20a%20free,reactions%20that%20damage%20animal%20cells.

-https://www.khanacademy.org/science/ap-biology/cellular-energetics/cellular-respiration-ap/a/intro-to-cellular-respiration-and-redox

-https://courses.lumenlearning.com/suny-wmopen-biology1/chapter/redox-reactions/

-https://studiousguy.com/examples-redox-reactions-everyday-life/

-https://www.hsph.harvard.edu/nutritionsource/antioxidants/

-https://www.btsa.com/en/history-antioxidants-food/#:~:text=In%20the%20use%20of%20the,originated%20during%20the%20smoking%20process.

-https://chem.libretexts.org/Courses/University_of_California_Davis/UCDemos/Breathalyzer#:~:text=Principle%3A%20The%20 breathalyzer%20is%20a,oxidized

-https://scienceprojectideasforkids.com/the-chemistry-of-fruit-browning/

-https://core-docs.s3.amazonaws.com/documents/asset/uploaded_file/374538/Book_ch_16_dot_2_application_of_redox_reactions.pdf

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