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Topic: Salt bridge  (Read 12231 times)

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Offline Schrödinger

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Salt bridge
« on: November 07, 2009, 01:44:45 AM »
Hey guys. I am in desperate need of an explanation regarding the salt bridge. Please do not post links of other posts related to the topic. I want someone to clearly explain this to me.

Why is a salt bridge used? - Age old question, yet I need a clear cut explanation.
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Offline UG

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Re: Salt bridge
« Reply #1 on: November 07, 2009, 01:49:52 AM »
To provide a path for movement of ions to complete the circuit, the ions compensate for the increasing positive and negative charges in the anode and cathode.

Offline Schrödinger

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Re: Salt bridge
« Reply #2 on: November 07, 2009, 01:53:15 AM »
Okay,  will be asking a series of questions... please bear with me.

Let me tell you what i know.
Since Zn becomes Zn2+, this beaker has excess positive charge in the form of Zn2+ ions.

Since Cu2+ from solution becomes Cu, this beaker has an excess negative charge in the form of SO4 2- ions.

To neutralize this charge, a salt bridge is used.

Is this right?
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Offline UG

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Re: Salt bridge
« Reply #3 on: November 07, 2009, 01:56:54 AM »
I guess you could say that it neutralises the charges. But not having a salt bridge is like having a gap between your wires in a circuit, of course the light bulb will not light.

Offline Schrödinger

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Re: Salt bridge
« Reply #4 on: November 07, 2009, 01:58:40 AM »
Now, what does a salt bridge actually do to the solutions/ions in the beakers? i.e, How does it neutralize those charges? Is there any chemical change involved?
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Offline UG

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Re: Salt bridge
« Reply #5 on: November 07, 2009, 02:02:40 AM »
No chemical change (you mean like precipitation or something?), if we have a KNO3 salt bridge, NO3- will move into the Zn2+/Zn half cell and K+ ions into the other one.

Offline Schrödinger

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Re: Salt bridge
« Reply #6 on: November 07, 2009, 02:05:45 AM »
So, you mean to say that the ions of the electrolyte inside the salt bridge will align themselves/move into the respective beakers so as to neutralize the opposite charges?
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Offline UG

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Re: Salt bridge
« Reply #7 on: November 07, 2009, 02:06:09 AM »
YES!

Offline Schrödinger

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Re: Salt bridge
« Reply #8 on: November 07, 2009, 02:08:33 AM »
What happens to the ions of the ZnSO4 and CuSO4 solutions? Do they move into the salt bridge as well, or is the movement a one-way process?

 i.e., only from the salt bridge and not into the salt bridge
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Offline UG

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Re: Salt bridge
« Reply #9 on: November 07, 2009, 02:11:25 AM »
i.e., only from the salt bridge and not into the salt bridge
Haha, well there is no way that you can just make this one way flow of ions happen so I presume that it is a two way thing.

Offline Schrödinger

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Re: Salt bridge
« Reply #10 on: November 07, 2009, 02:14:07 AM »
As a result of this 2-way movement, will we be able to notice any ZnCl2 well within the salt bridge and K2SO4 well within the salt bridge, presuming the electrolyte in the salt bridge to be KCl?
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Offline UG

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Re: Salt bridge
« Reply #11 on: November 07, 2009, 02:19:12 AM »
Are we talking about an inverted U-tube here? The ions are all there in solution, isolated ones like as Zn2+ or Cl- and SO42-, so yes, you will find Zn2+ and Cl- and SO42- and K+ ions in the salt bridge. By the way, I'm trying to eat baked beans and toast while typing this and it's a bit messy so if my thoughts are a bit messy, apologies.

Offline Schrödinger

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Re: Salt bridge
« Reply #12 on: November 07, 2009, 02:23:23 AM »
Now that we are OK with the neutralization part, here is another question:

Although there is some neutralization of the charges due to the ions of the salt bridge, will these ions not dissociate and move towards the oppositely charged electrode?

i.e., why should the neutralized molecules remain neutral?
"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
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Offline arjunarul

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Re: Salt bridge
« Reply #13 on: November 07, 2009, 02:29:28 AM »
Sorry to interrupt.

See this:
http://en.wikipedia.org/wiki/Daniell_cell

"In such a cell, the sulphate ions play an important role. Having a negative charge, these anions build up around the anode to maintain a neutral charge. Conversely, at the cathode the zinc (II) cations accumulate to maintain this neutral charge."

Where does the role of salt bridge ions come here.
What I thought of this line in Wikipedia is that the Zn2+ ions move to the Cu electrode and neutralize the SO42- ions and the SO42- ions move to the Zn electrode and neutralize the Zn2+ ions.

Is this right?

Offline UG

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Re: Salt bridge
« Reply #14 on: November 07, 2009, 02:31:06 AM »
Although there is some neutralization of the charges due to the ions of the salt bridge, will these ions not dissociate and move towards the oppositely charged electrode?

i.e., why should the neutralized molecules remain neutral?
Err.... what? I'm not sure I understand what you are asking

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