A simple chemical cell can be set up using copper and zinc electrodes. Here, we’ll show you how it...
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Transcript of A simple chemical cell can be set up using copper and zinc electrodes. Here, we’ll show you how it...
A simple chemical cell can be set up using copper and zinc electrodes. Here, we’ll show you how it works.
A Chemical Cell
The Copper-Zinc Cell
We’ll construct this cell. We start with two empty containers…
containers
We place a strip of copper metal in one of them. We call this a copper electrode.
Cucopper
electrode
A metal is composed of neutral atoms. We’ll show (click) a few neutral copper atoms on this electrode.
CuCu
Cu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
copper electrode
In the other container, we’ll place a piece of zinc metal, which we call the zinc electrode.
Cu ZnCu
Cu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
zinc electrode
We’ll show a few neutral zinc atoms (click) on this electrode.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
zinc electrode
We obtain an ammeter. A ammeter measures the rate of flow of electrons, or current.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
ammeter
A
We’ll attach the ammeter to each electrode using conducting wires.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
+–
+–A
wires
wires are composed of neutral atoms, which have the same number of protons as electrons.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
Wires are composed of neutral
atoms
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
Because protons are positive, we’ll represent protons in the wires by positive charges
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
protons
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
And electrons are negative, so we’ll represent electrons by negative charges.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
electrons
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
Protons in all materials are in fixed positions in the nuclei of atoms, so they don’t move in the wires.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
protons are infixed positions
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
But in metals, electrons can move easily
ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
Cu++++++++++++++++++
++
–––
––
–
+ +–––––––––––––– – –A
electrons
In the container with the copper electrode, we add some copper(II) nitrate solution
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
Cu(NO3)2
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
Copper(II) nitrate consists of (click) copper 2 plus ions and (click) nitrate ions. These ions are free to move around in the solution.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
Cu(NO3)2
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
The three copper 2+ ions we’ve represented here, have total charge of positive 6.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
+6
And the six nitrate ions we’ve represented have a total charge of negative 6, so at this point, charges are balanced in this solution.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
–6
In the beaker with the zinc electrode, we add zinc nitrate solution.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
Cu(NO3)2 Zn(NO3)2
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
Zinc nitrate solutions consists of (click) zinc 2 plus ions and (click) nitrate ions
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
Cu(NO3)2 Zn(NO3)2
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
The zinc 2+ ion we’ve represented here has a charge of positive 2.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
Cu(NO3)2 Zn(NO3)2
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
+2
And the two nitrate ions we’ve represented have total charge of negative 2. So at this point, charges are also balanced in this solution.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
Cu(NO3)2 Zn(NO3)2
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
–2
Between the two containers we add (click) an inverted U tube with a solution of a salt like potassium nitrate, KNO3.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
Cu(NO3)2 Zn(NO3)2
KNO3
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
We call this a salt bridge.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu 3NO
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
KNO3
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
KNO3 solution consists of K plus and NO3 minus ions. Like all ions in solutions, these ions are free to move.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+KNO3
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
Now we’ll focus on the zinc electrode and have a look at one of the zinc atoms.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
–
+–
+–A
–
This zinc atom loses two electrons and changes into a zinc 2 plus ion, as shown by the equation Zn gives Zn2+ plus 2 electrons. This ion then (click) leaves the metal and is dissolved in the solution.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–A
–2Zn Z
n–
Zn Zn2+ + 2e–
–
–
–
The electrons supplied by the zinc push the other electrons through the wire (click twice while watching)
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
–
AZn Zn2+ + 2e–
–
–
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
AZn Zn2+ + 2e–
–
Meanwhile, over at the copper electrode, a copper 2+ ion moves to the surface of the electrode.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
–––
AZn Zn2+ + 2e–
–
The two extra electrons on the copper electrode (click), move onto the Copper 2+ ion
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
2Cu
––
Zn Zn2+ + 2e–
–
The copper 2+ ion gains these electrons and changes into a neutral copper atom, as shown by the equation Cu2+ plus 2 electrons forms Cu.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
2Cu –Cu–
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
–
This whole process keeps repeating itself, causing electrons to continuously move through the ammeter.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
Cu(NO3)2 Zn(NO3)2
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
–
Now, we’ll focus on the ions in the container with the copper(II) nitrate solution
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
Cu(NO3)2
–
In our example, one copper(II) ion was used up.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
Cu(NO3)2
used up
–
The two copper ions that now remain, have a total charge of positive 4.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
+4
–
And the six nitrate ions have total charge of negative 6.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
–6
–
So there is an excess of negative charge in the solution in the container on the left.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
–
Now, we’ll focus on the container on the right, with the zinc nitrate solution.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
Zn(NO3)2
–
In our example, one zinc 2+ ion was produced…
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
Zn(NO3)2
produced
–
The two zinc 2+ ions that are now present, have total charge of positive 4
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
+4
–
And the two nitrate ions have a total charge of negative 2.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
–2
–
So there is an excess of positive charge in the solution in the container on the right.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
excess of positive charge
–
In order to balance charges, positive ions tend to move (click) toward the left through the salt bridge, away from the side with excess positive charge and toward the side with excess negative charge.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
2Zn 3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
K+
K+
K+
K+
3NO
3NO
3NO
3NO
3NO
3NO
K+
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
excess of positive charge
K+
–
And negative ions tend to (click) move toward the container on the right, away from the side with excess negative charge and toward the side with excess positive charge.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
3NO
3NO
3NO
3NO
3NO
3NO
3NO
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
excess of negative charge
excess of positive charge
K+
K+
K+K
+
K+
K+
2Zn
–
So the salt bridge is an important part of a chemical cell. It allows positive and negative ions to move through it so that the charges in the solutions remain balanced. Without a salt bridge, a chemical cell would not work.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
A
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
Allows ions to
move so charges
are balance
d
–
If we were to replace the ammeter with a voltmeter,
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
–
Under what are called standard conditions, this cell would initially have a voltage of 1.1 volts.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
Voltage = 1.1 volts
–
As this cell operates (click), zinc atoms will continue to dissolve to form zinc ions as they lose electrons…
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
–
And (click) copper 2+ ions will continue to gain electrons as they form copper atoms.
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
–
As zinc atoms on the zinc electrode dissolve,
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
Zinc atoms are dissolved
–
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
Cu2+ + 2e– Cu Zn Zn2+ + 2e–
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
Zinc atoms are dissolved
And copper 2+ ions in the copper(II) nitrate solution are used up, the voltage supplied by this cell will gradually decrease,
Cu2+ ions are used
up
–
Cu ZnZn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
Zn
ZnZ
nZn
ZnZ
nZn
Zn
CuCu Cu
CuCu Cu
CuCu Cu
CuCu Cu
CuCu
Cu
3NO
3NO
2Cu
2Cu
3NO3NO
3NO
3NO
3NO
salt bridge
++++++++++++++++++
++ –
––––––––
––– –––––––
+–
+–
2Zn
––––
V
Cu
K+
K+
K+K
+
K+
K+
2Zn 3NO
3NO
3NO 3NO
3NO
3NO
3NO
Zinc atoms are dissolved
and will over time, drop to zero.
Cu2+ ions are used
up
Voltage = 0 volts