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Glendy Gonzalez 1A
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Postby Glendy Gonzalez 1A » Sun Feb 18, 2018 9:06 pm

Is there a set of "rules" or order in which half-reactions should be balanced? Like do you add H20 or OH- first?

Bansi Amin 1D
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Re: "Rules"

Postby Bansi Amin 1D » Sun Feb 18, 2018 9:08 pm

I think it's that you start out balancing with water, and then use the hydroxide to balance the water.

Jiun Yue Chung 2I
Posts: 27
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Re: "Rules"

Postby Jiun Yue Chung 2I » Sun Feb 18, 2018 9:11 pm

In order to balance half-reactions, you often want to balance the O atoms in each first, which requires adding H2O on the other side of the equation. For instance, the half-reaction MnO4- -----> MnO2 has 4 O atoms on the left and 2 O atoms on the right. To balance, you add 2 H2O molecules to the right hand side (since H2O has two oxygens). From there, you balance the H atoms on the right side by adding H2Os to the left and simultaneously adding OH- ions to the right for each H2O. Hope that helps!

Srbui Azarapetian 2C
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Re: "Rules"

Postby Srbui Azarapetian 2C » Sun Feb 18, 2018 9:12 pm

You would add the H20 first to balance the oxygens, then balance hydrogens using H+, and after balancing the charges, convert the H+ to H20 by adding OH¯ to both sides. The side with the H+ will determine how many hydroxide to add.

Jason Muljadi 2C
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Joined: Thu Jul 27, 2017 3:01 am

Re: "Rules"

Postby Jason Muljadi 2C » Sun Feb 18, 2018 9:20 pm

The book has these set of rules that I've abided by that I think is pretty helpful. It's under Section 14.2.

Step 1. Identify the species being oxidized and the species being reduced by looking at the change of oxidation numbers.

Step 2. Write two skeletal equations (unbalanced) for oxidation and reduction half-equations

Step 3. Balance all the elements in the half-reaction except for the O and H atoms.

Step 4. In an acidic solution, balance the O's by using H2O and then balance the H by using H+. In basic solutions, balance O by using H2O; then balance H by adding H2O to the side of each half-reaction that needs H and adding OH- to the other side.

Step 5. Balance the electric charges by adding electrons to the left for reductions and to the right of oxidations until the charges on the two sides of the arrow are the same.

Step 6. If needed, multiply each half-reaction by the factor required to give equal numbers of electrons in the two half-reactions, and then add the two equations and include the physical states.

Step 7. Simply the appearance of the equation by canceling species that appear on both sides and check if the charges are balanced.

Hope this helps :)

Simrina Desar Dis 1H
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

Re: "Rules"

Postby Simrina Desar Dis 1H » Sun Feb 18, 2018 10:35 pm

If you forget to balance the reaction is there a way to find that you have made a mistake at the end? Is there something that indicates that your answer does not make sense?

Sarah 2F
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

Re: "Rules"

Postby Sarah 2F » Mon Feb 19, 2018 4:04 pm

You add the H20 first and then do the rest of the balancing

Alejandra Rios 1L
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Re: "Rules"

Postby Alejandra Rios 1L » Tue Feb 20, 2018 1:40 pm

14.1 and 14.2 in the book displays two different sets of rules that you can follow!

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