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Introduction

Reaction Types in Grade 11 discussed oxidation , reduction and redox reactions . Oxidation involves a loss of electrons and reduction involves a gain of electrons . A redox reaction is a reaction where both oxidation and reduction take place. What is common to all of these processes is that they involve a transfer of electrons and a change in the oxidation state of the elements that are involved.

Oxidation and reduction

  1. Define the terms oxidation and reduction .
  2. In each of the following reactions say whether the iron in the reactants is oxidised or reduced.
    1. F e F e 2 + + 2 e -
    2. F e 3 + + e - F e 2 +
    3. F e 2 O 3 + 3 C O 2 F e + 3 C O 2
    4. F e 2 + F e 3 + + e -
    5. F e 2 O 3 + 2 A l A l 2 O 3 + 2 F e
  3. In each of the following equations, say which elements in the reactants are oxidised and which are reduced.
    1. C u O ( s ) + H 2 ( g ) C u ( s ) + H 2 O ( g )
    2. 2 N O ( g ) + 2 C O ( g ) N 2 ( g ) + 2 C O 2 ( g )
    3. M g ( s ) + F e S O 4 ( a q ) M g S O 4 ( a q ) + F e ( s )
    4. Z n ( s ) + 2 A g N O 3 ( a q ) 2 A g + Z n ( N O 3 ) 2 ( a q )
  4. Which one of the substances listed below acts as the oxidising agent in the following reaction? 3 S O 2 + C r 2 O 7 2 - + 2 H + 3 S O 4 2 - + 2 C r 3 + + H 2 O
    1. H +
    2. Cr 3 +
    3. SO 2
    4. Cr 2 O 7 2 -

In Grade 11, an experiment was carried out to see what happened when zinc granules are added to a solution of copper(II) sulphate. In the experiment, the Cu 2 + ions from the copper(II) sulphate solution were reduced to copper metal, which was then deposited in a layer on the zinc granules. The zinc atoms were oxidised to form Zn 2 + ions in the solution. The half reactions are as follows:

C u 2 + ( a q ) + 2 e - C u ( s ) (reduction half reaction)

Z n ( s ) Z n 2 + ( a q ) + 2 e - (oxidation half reaction)

The overall redox reaction is:

C u 2 + ( a q ) + Z n C u ( s ) + Z n 2 + ( a q )

There was an increase in the temperature of the reaction when you carried out this experiment. Is it possible that this heat energy could be converted into electrical energy? In other words, can we use a chemical reaction where there is an exchange of electrons, to produce electricity? And if this is possible, what would happen if an electrical current was supplied to cause some type of chemical reaction to take place?

An electrochemical reaction is a chemical reaction that produces a voltage , and therefore a flow of electrical current. An electrochemical reaction can also be the reverse of this process, in other words if an electrical current causes a chemical reaction to take place.

Electrochemical reaction

If a chemical reaction is caused by an external voltage, or if a voltage is caused by a chemical reaction, it is an electrochemical reaction.

Electrochemistry is the branch of chemistry that studies these electrochemical reactions. In this chapter, we will be looking more closely at different types of electrochemical reactions, and how these can be used in different ways.

The galvanic cell

Experiment : electrochemical reactions

Aim:

To investigate the reactions that take place in a zinc-copper cell

Apparatus:

zinc plate, copper plate, measuring balance, zinc sulphate (ZnSO 4 ) solution (1 mol.dm - 3 ), copper sulphate (CuSO 4 ) solution (1 mol.dm - 3 ), two 250 ml beakers, U-tube, Na 2 SO 4 solution, cotton wool, ammeter, connecting wire.

Method:

  1. Measure the mass of the copper and zinc plates and record your findings.
  2. Pour about 200 ml of the zinc sulphate solution into a beaker and put the zinc plate into it.
  3. Pour about 200 ml of the copper sulphate solution into the second beaker and place the copper plate into it.
  4. Fill the U-tube with the Na 2 SO 4 solution and seal the ends of the tubes with the cotton wool. This will stop the solution from flowing out when the U-tube is turned upside down.
  5. Connect the zinc and copper plates to the ammeter and observe whether the ammeter records a reading.
  6. Place the U-tube so that one end is in the copper sulphate solution and the other end is in the zinc sulphate solution. Is there a reading on the ammeter? In which direction is the current flowing?
  7. Take the ammeter away and connect the copper and zinc plates to each other directly using copper wire. Leave to stand for about one day.
  8. After a day, remove the two plates and rinse them first with distilled water, then with alcohol and finally with ether. Dry the plates using a hair dryer.
  9. Weigh the zinc and copper plates and record their mass. Has the mass of the plates changed from the original measurements?

Questions & Answers

Do polymers form restrictedly only if compound is saturated, only?
milani Reply
what is a free fall?
Beyanca Reply
is when The Only Force acting On an Object is Gravitational Force
Madman
Thats right
Beyanca
then Why ask when you Know the answer?
Madman
She's just helping those who forgot it...bro
Thato
guys I need help on Getting ready for a last minute test
Kenelioe Reply
what help you need
Neil
we'll I'm in grade 12 so we doing this topic about upac thing
Kenelioe
on What?
Madman
the organic molecule section
Kenelioe
IUPAC NAMING WHICH FUNCTIONAL GROUP YOU CANNOT NAME?SO I COULD HELP YOU
Madman
ester
Sboniso
you should also look at structural isomers. Its crucial that they might add that one. also try and write down the structural formula of all the given compounds on the table
milani
hi guys i can explain everything in terms of physics and chemistry
Neil Reply
๐Ÿ˜‚๐Ÿ˜‚๐Ÿ˜‚๐Ÿ˜‚๐Ÿ˜‚
Madman
yes
Lucky
yea
Kenelioe
guys 2mrrow I'm writing a test in chemistry I need help
Kenelioe
Hi guys. Can anyone please tell me what a functional group is?
Samukelo
a functional group depends on how many bonds there are between carbon atoms, if there are single bonds all the way it's an alkane, if there is a presence of at least one double bond it's a Alkene and if there's at least one triple bond it's an alkyne.
Olive
which quantity is measured in Watt?
Saara Reply
work
Absai
explain for me absai
Sboniso
is Power Not Work work is Measured In Joules it has Energy
Madman
thanks
Saara
Pleasure
Madman
what is galvanic cell ?
Oratile Reply
is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell.
Hope
how to understand alkane names
Sboniso Reply
suffix Ane in the IUPAC NAMING
Madman
elaborate a little more plz
Kenelioe
Alkanes are Saturated Meaning they don't have Multiple Bonds between Carbon Atoms and When you are Naming THEM THEY MUST END WITH (-ANE ) GET ME?
Madman
What are hydrocarbons
Phelo Reply
are organic Compounds with only Carbon and Hydrogen Atoms
Madman
whats the difference between aldehydes and ketones
Angel Reply
definition of chain parent
Lea Reply
what is wave?
Agness Reply
when butane burns in an excess of oxygen ,the products are
Slay
CO2 and H2O
GARY
Carbon dioxide and Water...
Thato
what is hydrocarbon
Ntswaki Reply
Hydrocarbon is a compostion of mainy carbon and hydrogen
Tsion
hydrocarbon compound made up of carbon and hydrogen only
Thembelani
25 element of physics
musah Reply
an object will remain at rest or move at a constant velocity unless acted upon a net force
Lebogang Reply
thank you
Thabiso
law of inertia
Joan
an object resisting the change in velocity.
Thabiso
newton first law of motion
Tshepo
An object will remain at rest, unless an unbalanced force acts on it.
Anga
or uniform motion
Thato
What is a molecule
Thabiso Reply
a molecule is a simplest structure unite of an elements
Else
thank you
Thabiso
Plz remind me the 1st Newton's law
Thabiso

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Source:ย  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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