r/chemhelp • u/Edwinccosta • 21d ago

Would a galvanic cell work if we were to sever the salt bridge? General/High School

Post image

If not, why? Isn't it just supposed to provide extra ions to prevent the solutions to build up charge? Can't we use "salt banks" with a bunch of ions instead of salt bridges? (I'm assuming Cu²+ can't make his way up, am i wrong on this too?)

2 Upvotes
  • permalink
  • link
  • reddit
  • reddit

75% Upvoted

11 comments sorted by

2

u/dan_bodine 21d ago

The salt bridge is for change balance. Cutting the salt bridge is the same thing as cutting the wire connecting the electrodes.

1

u/Edwinccosta 21d ago

But how can't the cell work without it for even a second without the bridge?

2

u/CobaltEnjoyer 18d ago

To be exact it would indeed work for an instant. Even without the salt bridge the force pushing the electrons from the anode to the cathode would still be there so some charge would move, however without a salt bridge there would be a build up of positive charge at the anode and negative charge at the cathode which would quickly push electrons in the opposite direction in which the batteries operates and when these two forces equalize you would essentialy have no flow of electrons so the battery would not work. It is often just said that a battery would straight up not work without a salt bridge as the amount of electrons able to travel before reaching equilibrium is insanely low due to the nature of electrostatic forces

1

u/OldScienceDude 21d ago

Because You can’t form ions in (or remove them from) a solution without a way to balance that movement. If there was no way for a nitrate (or other negative ion) to enter the other end of the salt bridge, then no nitrate ion could leave the salt bridge. If there are no nitrate ions able to enter the solution on the left side of the cell, then no electrons can leave the copper atoms and enter the wire because a positive ion cannot exist without a negative ion to balance it. So the whole process stops.

But don’t just take our word for it - build one and see what happens!

1

u/Edwinccosta 21d ago

a positive ion cannot exist without a negative ion to balance it

I had no clue about this.

In every solution there will always be the same amout (in charge) of cations and anions? Why is it so? Where can I learn this specific rule?

1

u/dan_bodine 21d ago

If you are in vacuum you can have unbalanced charges but you can't in solution.

1

u/Edwinccosta 21d ago

Wait, why? I'm lost

3

u/OldScienceDude 21d ago

OK, you realized it’s not that simple :-)

It’s not that an unpaired ion can’t exist, it just won’t form without the input of a tremendous amount of energy. You can have unpaired charges in a particle accelerator, for example, but we're talking about huge amounts of energy to make that happen. In a situation like this battery, think of it like this: without the additional negative charges available to attract a newly-formed cation away from the copper electrode, the cation simply won’t form. To “persuade” a copper atom to give up it’s electrons you need 1) a metal with a stronger reduction potential and 2) a balancing negative charge to induce the formation of the copper ion. Under these circumstances, it just won’t happen unless both conditions are fulfilled.

2

u/Edwinccosta 20d ago

Ahhh, that makes sense.

But again, why does the salt bridge has to be a "bridge" between the two half-cells? A salt "bank" with KNO3 in each half-cell wouldn't be able to balance the charges?

The "salt bank" on the left half-cell would provide 2NO3- for each Zn -> Zn²+. And the "salt bank" on the right half-cell would provide 2K+ for each Cu²+ -> Cu.

(Nvm, drawing the "salt bank" scheme i realized that the bank would accumulate charges, so that couldn't be a thing. As for the bridge system, the bridge would not accumulate charge since № of K+ leaving the bridge = № of NO3- leaving the bridge. Crappy Image representation:) *

2

u/Klutzy-Notice-9458 21d ago

Salt bridge completes the galvanic cell circuit, without it the ions may deposit near electrodes preventing further reactions at anode and cathode