[phillyj]

Hi all, I needed to figure out the redox reaction for oxidation of glucose by ferricyanide ion to gluconic acid for an experiment but I'm not sure where to start. Heres what I know:

Fe(CN)₆^3- +e- => Fe(CN)₆^4-
C₆H₁₂O₆ => C₆H₁₂O₇

the glucose has me confused and its been a while since I did redox rxns so I'm reviewing them now. I don't know where to start. Please help. Thanks

[Borek]

Write half cell reaction balancing oxygen & hydrogen with water and H⁺, it will become obvious how many electrons are consumed by glucose.

[phillyj]

So i tried to work it out and this is what I got:

C₆H₁₂O₆ + H₂O + 2e- <=> C₆H₁₂O₇ + 2H+

Fe(CN)₆^4- <=> Fe(CN)₆^3- + e-
-----------------------------------------------------------------------------

C₆H₁₂O₆ + 2Fe(CN)₆^4- + H₂O <=> C₆H₁₂O₇ + 2H+ + Fe(CN)₆^3-

Is this correct?

[AWK]

Check material and charge balances

[phillyj]

i don't under stand what you mean. i balanced the oxygen with water and balanced the water with H+
glucose, gluconic acid and water have no charge so i balnced the 2H+ with 2 e-

what did i do wrong?

[Borek]

what did i do wrong?

Please check if your half reactions are balanced. Your approach was correct, but execution disastrous.

[phillyj]

i been looking over what i wrote and don't see whats wrong. i may be at that point of the day where nothing is making sense.

edit: you mean i forgot the 2 in front of the Fe(CN)₆^3-? stupid typo. I got it right on paper, then

[Borek]

C₆H₁₂O₆ + H₂O + 2e- <=> C₆H₁₂O₇ + 2H+

Is charge balanced in this equation?

[phillyj]

C₆H₁₂O₆ + H₂O + 2e- <=> C₆H₁₂O₇ + 2H+

Is charge balanced in this equation?

Isn't it? the glucose and gluconic acid have no charge so all i need is to add 2 e- to balance the 2 H+, right?
I'm more confused than ever.

[Borek]

Since when -2 = +2?

[Schrödinger]

So i tried to work it out and this is what I got:

C₆H₁₂O₆ + H₂O + 2e- <=> C₆H₁₂O₇ + 2H+

Fe(CN)₆^4- <=> Fe(CN)₆^3- + e-
-----------------------------------------------------------------------------

C₆H₁₂O₆ + 2Fe(CN)₆^4- + H₂O <=> C₆H₁₂O₇ + 2H+ + Fe(CN)₆^3-

Is this correct?

Probably logical reasoning will help you...

Glucose is getting oxidized by ferricyanide ion to gluconic acid, and hence ferricyanide ion is being reduced to ferrocyanide ion.

Since oxidation is the loss of electrons, glucose has to lose electrons. Now see your first equation.

Since reduction is the gain of electrons, ferricyanide ion has to gain electrons. Now look at your 2nd equation...you might want to reverse it, because otherwise your final equation states that there is no reduction taking place, just oxidation. This is quite absurd, since reduction and oxidation are complementary processes. One cannot occur without the other

I hope this helps

[phillyj]

i figured it out a couple hours ago. as I said previously, I wasn't thinking straight. That's why I kept overlooking the obvious. Sorry about that and the help was greatly appreciated.