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

copper electrode

In the other container, we’ll place a piece of zinc metal, which we call the zinc electrode.

Cu ZnCu

CuCu Cu

zinc electrode

We’ll show a few neutral zinc atoms (click) on this electrode.

Cu ZnZn

CuCu Cu

zinc electrode

We obtain an ammeter. A ammeter measures the rate of flow of electrons, or current.

Cu ZnZn

CuCu Cu

ammeter

We’ll attach the ammeter to each electrode using conducting wires.

Cu ZnZn

CuCu Cu

wires are composed of neutral atoms, which have the same number of protons as electrons.

Cu ZnZn

CuCu Cu

Wires are composed of neutral

++++++++++++++++++

++ –

––––––––

––– –––––––

Because protons are positive, we’ll represent protons in the wires by positive charges

Cu ZnZn

CuCu Cu

protons

++++++++++++++++++

++ –

––––––––

––– –––––––

And electrons are negative, so we’ll represent electrons by negative charges.

Cu ZnZn

CuCu Cu

electrons

++++++++++++++++++

++ –

––––––––

––– –––––––

Protons in all materials are in fixed positions in the nuclei of atoms, so they don’t move in the wires.

Cu ZnZn

CuCu Cu

protons are infixed positions

++++++++++++++++++

++ –

––––––––

––– –––––––

But in metals, electrons can move easily

CuCu Cu

Cu++++++++++++++++++

–––

––

+ +–––––––––––––– – –A

electrons

In the container with the copper electrode, we add some copper(II) nitrate solution

Cu ZnZn

CuCu Cu

Cu(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

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

CuCu Cu

2Cu 3NO

3NO3NO

Cu(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

The three copper 2+ ions we’ve represented here, have total charge of positive 6.

Cu ZnZn

CuCu Cu

2Cu 3NO

3NO3NO

++++++++++++++++++

++ –

––––––––

––– –––––––

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

CuCu Cu

2Cu 3NO

3NO3NO

++++++++++++++++++

++ –

––––––––

––– –––––––

In the beaker with the zinc electrode, we add zinc nitrate solution.

Cu ZnZn

CuCu Cu

2Cu 3NO

3NO3NO

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

Zinc nitrate solutions consists of (click) zinc 2 plus ions and (click) nitrate ions

Cu ZnZn

CuCu Cu

2Zn 3NO

2Cu 3NO

3NO3NO

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

The zinc 2+ ion we’ve represented here has a charge of positive 2.

Cu ZnZn

CuCu Cu

2Zn 3NO

2Cu 3NO

3NO3NO

Cu(NO3)2 Zn(NO3)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

CuCu Cu

2Zn 3NO

2Cu 3NO

3NO3NO

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

Between the two containers we add (click) an inverted U tube with a solution of a salt like potassium nitrate, KNO3.

Cu ZnZn

CuCu Cu

2Zn 3NO

2Cu 3NO

3NO3NO

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

We call this a salt bridge.

Cu ZnZn

CuCu Cu

2Zn 3NO

2Cu 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

KNO3 solution consists of K plus and NO3 minus ions. Like all ions in solutions, these ions are free to move.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

K+KNO3

++++++++++++++++++

++ –

––––––––

––– –––––––

Now we’ll focus on the zinc electrode and have a look at one of the zinc atoms.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

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

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

–2Zn Z

Zn Zn2+ + 2e–

The electrons supplied by the zinc push the other electrons through the wire (click twice while watching)

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

AZn Zn2+ + 2e–

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

AZn Zn2+ + 2e–

Meanwhile, over at the copper electrode, a copper 2+ ion moves to the surface of the electrode.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

–––

AZn Zn2+ + 2e–

The two extra electrons on the copper electrode (click), move onto the Copper 2+ ion

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

––

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

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

2Cu –Cu–

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

This whole process keeps repeating itself, causing electrons to continuously move through the ammeter.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

Cu(NO3)2 Zn(NO3)2

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

Now, we’ll focus on the ions in the container with the copper(II) nitrate solution

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

Cu(NO3)2

In our example, one copper(II) ion was used up.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

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

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

And the six nitrate ions have total charge of negative 6.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

So there is an excess of negative charge in the solution in the container on the left.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

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

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

Zn(NO3)2

In our example, one zinc 2+ ion was produced…

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

Zn(NO3)2

produced

The two zinc 2+ ions that are now present, have total charge of positive 4

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

And the two nitrate ions have a total charge of negative 2.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

So there is an excess of positive charge in the solution in the container on the right.

Cu ZnZn

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

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

CuCu Cu

2Zn 3NO

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

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

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

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

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

2Zn 3NO

3NO 3NO

Allows ions to

move so charges

are balance

If we were to replace the ammeter with a voltmeter,

Cu ZnZn

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

2Zn 3NO

3NO 3NO

Under what are called standard conditions, this cell would initially have a voltage of 1.1 volts.

Cu ZnZn

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

2Zn 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

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

2Zn 3NO

3NO 3NO

And (click) copper 2+ ions will continue to gain electrons as they form copper atoms.

Cu ZnZn

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

2Zn 3NO

3NO 3NO

As zinc atoms on the zinc electrode dissolve,

Cu ZnZn

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

2Zn 3NO

3NO 3NO

Zinc atoms are dissolved

Cu ZnZn

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

Cu2+ + 2e– Cu Zn Zn2+ + 2e–

2Zn 3NO

3NO 3NO

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

Cu ZnZn

CuCu Cu

3NO3NO

salt bridge

++++++++++++++++++

++ –

––––––––

––– –––––––

––––

2Zn 3NO

3NO 3NO

and will over time, drop to zero.

Cu2+ ions are used

Voltage = 0 volts

a simple chemical cell can be set up using copper and zinc electrodes. here, we’ll show you how it...

neutral copper atoms

neutral zinc atoms

nitrate ions weve

zinc electrodes

strip of copper metal

piece of zinc metal

nuclei of atoms

negative charges

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