ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Redox Reactions (oxidation, reduction), process of making aluminium and Galvanic, Alkaline and Zin-Carbon cell and more

Updated on August 12, 2012

Definition of redox reaction


A redox reaction is the transfer of electrons, where one of the reactants involved will lose charge and the other one will gain charge. Note that acid / base reactions transfer protons (H+) and not electrons.

A redox reaction will happen spontaneously if the “S-slide” rule is fulfilled. The higher the atom on the left side is compared to the atom on the right side, the steeper the “slide” will be and the easier they react.


Oxidation numbers

The oxidation number tells the amount of electrons of an atom in a molecule, which it would have if all the other ligands were removed.
The rule is simple. One takes the valence electrons of a molecule (which can be found on the table of elements) and substrates its formally assigned number of electrons. The formally assigned number of electrons depends on the electronegativity of the atom itself and the atom it shares the electrons with. If the atom has a higher electronegativity than the other atom it makes a bound to, then it will “get” its electrons and the formally assigned electron number will increase. The number is represented with Roman numbers.

Source


In the example above, one can see that the oxidation number of carbon is -3 (-III). Its valence electron number is 4 (IV). Three more electrons are assigned to it, as it has a higher electronegativity than hydrogen (electronegativity of hydrogen: 2,1; electronegativity of carbon: 2,5). So, the total amount of assigned electrons is four (which it already had before) plus three of hydrogen (which it “took away”). By subtracting, it gives -3 (-III).

A lot easier are ions and molecular compounds like hydrogen (H2), oxygen (O2) etc. The oxidation number of ions is simply its charge. The oxidation number between molecules such as hydrogen, oxygen etc. is always 0.

With oxidation numbers, redox reactions can also be carried out.
Example: C (-I) ->C (+III) + 4e- (oxidation)
Carbon has been oxidized, as it has given off four electrons.
Example 2: Mn (+VII) + 3e- ->Mn (+IV) (reduction)
Manganese

Source

Galvanic cell

The right-hand side has a copper cathode, which is in a solution of nitrate ions (NO3-) and copper ions (Cu2+). The copper ions will be reduced, since the electron flow goes through the copper anode and the solution. The copper ions will form a layer of copper on the anode. The anode does not have to be necessarily made of copper. It can be another non-reactive metal like platinum. The electron flow continues through the salt bridge, which has on each opening a cotton plug in order to prevent any unwished ions going into the salt bridge. The salt bridge is sodium ions (Na2+) and nitrate ions (NO3-). Without these ions, the electrons could not be able to find a way to the left-hand side. The left-hand side has a solution of zinc ions (Zn2+) and nitrate (NO3). The zinc is oxidized there and the zinc anode will be eventually used up as it releases steadily new zinc ions and thus also releasing electrons which go upwards. The electron flow continues through a voltmeter, which measures the voltage of the electron flow respectively the cell potential (energy!). The cycle is closed when the electrons reach the copper cathode and the process starts from the beginning again.

Cell potential


The cell potential is the energy, which a cell has in a spontaneous reaction. It can be easily calculated by subtracting the normal potentials of the reduction reaction and the oxidation by the following formula (the normal potential of a reaction can be normally read off on a redox reaction table):
Normal potential (V) = (REDUCTION) – (OXIDATION)


Carbon-Zinc cell

This cell type is separated by a mere separation paper in order to prevent any unwished reactions. The inner rod is a graphite (carbon) rod (negative end) which stays unreactive. In between the graphite rod and the separation paper is manganese dioxide (MnO2), which is capable of conducting electrons from the positive to the negative end. Manganese dioxide (MnO2) will be oxidized during this process. Right after the manganese dioxide, there is an electrolyte which is responsible for conducting the electrons to the manganese dioxide. In this case, the electrolyte is ammonium chloride (NH4Cl [aq]). The outer ends are the positive ends which consist of zinc, reducing it.
Oxidation: Zn <=> Zn2+ + 2e-
Reduction: MnO2 + e- + H+ <=> MnO(OH)

Alkaline battery

The reactions happening are actually the same as in a carbon-zinc cell. The only difference is that the electrolyte is not ammonium chloride (NH4Cl), but potassium hydronium (KOH) (aq). This electrolyte forms a soluble compound Zn(OH)42-, which prevents the death of a battery or cell, since there is no crust formed.

Build-up of an aluminium electrolysis

Source

Aluminum electrolysis cell

The aluminium electrolysis cell was the first invention, which allowed a cheap mass production of aluminium.
As it can be seen in the picture, the anode (positive end) is made out of huge carbon beakers, which reduce oxygen ions. The lower part is molten aluminium, where aluminium is oxidized. The aluminium comes from bauxite, which is a mixture of several molecules and since aluminium is very difficult to be gained from bauxite, a catalysator is used. It is cryolite, which is a salt (Na3AlF6).
The advantage of this way of producing aluminium is that the reduction needs oxygen and oxygen is everywhere anyway. The disadvantage of this is that huge amounts of energy are used in order to produce aluminium.
Reduction: 2O2- -> O2 + 4e-
Oxidation: Al3+ + 3e- -> Al

Principle of Rechargeable batteries

Principle: The principle is quite easy. By charging a battery, the electron circuit (flow) is reversed, and thus, the redox reaction is reversed. This is possible, because the compounds, which are formed during normal activities of a battery, stick to the electrodes (anode and cathode). Logically, the reversed electron circuit will go through these electrodes and reduce respectively oxidize the compounds.

Picture of a PEM fuel cell

Source

Example of a PEM (proton exchange membrane) fuel cell

The corresponding reactions are:
Oxidation: H2 -> 2H+ + 2e-
Reduction: O2 ->2O2- + 4e-
On the left-hand side, hydrogen (H2) is inserted, where it will be oxidized catalytically and these new hydrogen cations (or protons) pass a n electrolyte. On the right-hand side, air, O2, is inserted, where it will react with the protons (H+) and form water and release heat.
This is quite good for global warming as PEM fuel cells do not produce any carbon dioxide (CO2) (other batteries do produce CO2).

Comments

    0 of 8192 characters used
    Post Comment

    • mbyL profile imageAUTHOR

      Slaven Cvijetic 

      6 years ago from Switzerland, Zurich

      @punkhawk Thank you for your comment!

    • pinkhawk profile image

      pinkhawk 

      6 years ago from Pearl of the Orient

      Thank you very much for the idea about redox, I always heard this word but can't really understand it.

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)