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# Unit 5 help Watch

1. Hi, there's two questions that I'm slightly confused on regarding their answers. For the first one, I don't understand why 12e- are on the products side, as although this balances the equation, 12e- were not lost in terms of oxidation numbers. Also, could anyone help on explaining an answer for the second question. Thank you
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2. (Original post by candyhearts)
Hi, there's two questions that I'm slightly confused on regarding their answers. For the first one, I don't understand why 12e- are on the products side, as although this balances the equation, 12e- were not lost in terms of oxidation numbers. Also, could anyone help on explaining an answer for the second question. Thank you
The half equation for the first question is:

C2H5OH + 3 H2O ----> 2 CO2 + 12 H+ + 12 e-.

Start off by having:

C2H5OH ----> CO2.

You then balance the carbons:

C2H5OH ----> 2 CO2.

Then balance the oxygens with water molecules:

C2H5OH + 3 H2O ----> 2 CO2.

You then balance the hydrogen atoms with protons (H+ ions):

C2H5OH + 3 H2O ----> 2 CO2 + 12 H+.

You then balance the overall charge using electrons:

C2H5OH + 3 H2O ----> 2 CO2 + 12 H+ + 12 e-.
3. (Original post by thegodofgod)
The half equation for the first question is:

C2H5OH + 3 H2O ----> 2 CO2 + 12 H+ + 12 e-.

Start off by having:

C2H5OH ----> CO2.

You then balance the carbons:

C2H5OH ----> 2 CO2.

Then balance the oxygens with water molecules:

C2H5OH + 3 H2O ----> 2 CO2.

You then balance the hydrogen atoms with protons (H+ ions):

C2H5OH + 3 H2O ----> 2 CO2 + 12 H+.

You then balance the overall charge using electrons:

C2H5OH + 3 H2O ----> 2 CO2 + 12 H+ + 12 e-.
Usually I'd first consider the electrons, how come that doesn't work with this example?
4. (Original post by candyhearts)
Usually I'd first consider the electrons, how come that doesn't work with this example?
It does:

The overall charge in C2H5OH is 0, as it is a neutral compound. Each H atom has an oxidation state of +1 and each O atom has an oxidation state of of -2.

Therefore algebraically, you have the following equation:

2C + 6(+1) + (-2) = 0

2C + 6(+1) = 2

2C = -4

C = -2.

This means that the oxidation state of each C atom in each C2H5OH molecule is -2. However, as there are 2 C atoms per molecule of C2H5OH, the total oxidation states of the C atoms is 2(-2) = -4.

The overall charge in CO2 is 0, as it is a neutral compound. Each O atom has an oxidation state of -2.

Therefore algebraically, you have the following equation:

C + 2(-2) = 0

C = +4.

This means that the oxidation state of each C atom in each CO2 molecule is +4.

However, bearing in mind that there are 2 molecules of CO2 in the reaction, the total oxidation state of both C atoms in 2 CO2 is 2(+4) = +8.

Okay, so going from an oxidation state from -4 to +8 requires a loss of: 8 - (-4) = 12 electrons.

Therefore, you add 12 electrons to the products side.

I hope this is clear enough
5. (Original post by thegodofgod)
It does:

The overall charge in C2H5OH is 0, as it is a neutral compound. Each H atom has an oxidation state of +1 and each O atom has an oxidation state of of -2.

Therefore algebraically, you have the following equation:

2C + 6(+1) + (-2) = 0

2C + 6(+1) = 2

2C = -4

C = -2.

This means that the oxidation state of each C atom in each C2H5OH molecule is -2. However, as there are 2 C atoms per molecule of C2H5OH, the total oxidation states of the C atoms is 2(-2) = -4.

The overall charge in CO2 is 0, as it is a neutral compound. Each O atom has an oxidation state of -2.

Therefore algebraically, you have the following equation:

C + 2(-2) = 0

C = +4.

This means that the oxidation state of each C atom in each CO2 molecule is +4.

However, bearing in mind that there are 2 molecules of CO2 in the reaction, the total oxidation state of both C atoms in 2 CO2 is 2(+4) = +8.

Okay, so going from an oxidation state from -4 to +8 requires a loss of: 8 - (-4) = 12 electrons.

Therefore, you add 12 electrons to the products side.

I hope this is clear enough
Thank you so much Looking at it now, I'm not sure why I was even confused in the first place as they way you've explained it makes so much sense

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