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Note: A voltmeter can also be used in place of the ammeter. A voltmeter will measure the potential difference across the cell.

Results:

During the experiment, you should have noticed the following:

  • When the U-tube containing the Na 2 SO 4 solution was absent, there was no reading on the ammeter.
  • When the U-tube was connected, a reading was recorded on the ammeter.
  • After the plates had been connected directly to each other and left for a day, there was a change in their mass. The mass of the zinc plate decreased, while the mass of the copper plate increased.
  • The direction of electron flow is from the zinc plate towards the copper plate.

Conclusions:

When a zinc sulphate solution containing a zinc plate is connected by a U-tube to a copper sulphate solution containing a copper plate, reactions occur in both solutions. The decrease in mass of the zinc plate suggests that the zinc metal has been oxidised. The increase in mass of the copper plate suggests that reduction has occurred here to produce more copper metal. This will be explained in detail below.

Half-cell reactions in the zn-cu cell

The experiment above demonstrated a zinc-copper cell. This was made up of a zinc half cell and a copper half cell .

Half cell

A half cell is a structure that consists of a conductive electrode surrounded by a conductive electrolyte. For example, a zinc half cell could consist of a zinc metal plate (the electrode) in a zinc sulphate solution (the electrolyte).

How do we explain what has just been observed in the zinc-copper cell?

  • Copper plate At the copper plate, there was an increase in mass. This means that Cu 2 + ions from the copper sulphate solution were deposited onto the plate as atoms of copper metal. The half-reaction that takes place at the copper plate is: C u 2 + + 2 e - C u (Reduction half reaction) Another shortened way to represent this copper half-cell is Cu 2 + /Cu.
  • Zinc plate At the zinc plate, there was a decrease in mass. This means that some of the zinc goes into solution as Z 2 + ions. The electrons remain on the zinc plate, giving it a negative charge. The half-reaction that takes place at the zinc plate is: Z n Z n 2 + + 2 e - (Oxidation half reaction) The shortened way to represent the zinc half-cell is Zn/Zn 2 + . The overall reaction is: Z n + C u 2 + + 2 e - Z n 2 + + C u + 2 e - or, if we cancel the electrons: Z n + C u 2 + Z n 2 + + C u For this electrochemical cell, the standard notation is:
    Z n | Z n 2 + | | C u 2 + | C u
    where
    | = a phase boundary ( solid / aqueous ) | | = the salt bridge

In the notation used above, the oxidation half-reaction at the anode is written on the left, and the reduction half-reaction at the cathode is written on the right. In the Zn-Cu electrochemical cell, the direction of current flow in the external circuit is from the zinc electrode (where there has been a build up of electrons) to the copper electrode.

Components of the zn-cu cell

In the zinc-copper cell, the copper and zinc plates are called the electrodes . The electrode where oxidation occurs is called the anode , and the electrode where reduction takes place is called the cathode . In the zinc-copper cell, the zinc plate is the anode and the copper plate is the cathode.

Questions & Answers

Is the normal force always 0
Mpilo Reply
define the term rate of reaction in word
David Reply
I think it a chemical process in which substance act mutually on each other.
Sphesihle
how many bones are in the human body?
Asali
what is wave lengh
mama Reply
is the de broglie wavelength of the particle
Hope
calcium and magnesium, which one can displace aluminum from its compound?
Markia Reply
how is aluminum ion formed?
Dickens
molecules with the same molecular formula but different chain
Malaza Reply
what will be the answer
.angel
chain isomer
Anele
what does the newton's law says?
there are 3 newtons laws which are newton's law of universal gravitation, law of cooling, law of motion
Imagine
Did the feather or leaf hit the ground first?
Shaloom Reply
leaf
Pradip
2 to 30 minut long distance race 20 km what's the avarage speed for the race
Jamilla Reply
what is meaning of covalent bonds
Lungani Reply
bonds that exists between non metal atoms. each atom contribute electron(s) which will form a bond joining the two atoms. electrons in the bond now belongs to both atoms
Matome
how do we name haloalkanes
Thobeka Reply
how do we name haloalkanes
lesedi
what are examples of haloalkanes
Mpho
haloalkanes are compounds that consist of the halogen group chlorine bromine flourine and so on like 2-bromobutan
Samkele
give an example of calculating work
Nwabisa Reply
what is chain Isomer?
Christian Reply
chain isomer ar compounds with the same molecular formular but different chain length
Samkele
Where does the functional group of ketone in carbons belong
Keletso Reply
alkane
Isamkele
how can I find the structural formulae and IUPAC names of hexane?
Matshidiso Reply
@Matshidiso identify your compound which is an alkane..the general formula for alkane is CnH2n+2... hex-6 substitute n with 6 implying that you'll have 6 carbons and 14 Hydrogens then you can draw your structural formula *NB* every carbon has to have 4 bonds
Kgabo
what are disadvantages of primary cells and advantage of secondary cells?
Thabang Reply

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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