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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

how does the earth revolute
Kevin Reply
What is the momentum
Given Reply
The product of the object's mass and it's velocity
Mvula
electric field def
FREENCO
how is ester formed
Aubrey Reply
how is n ester formed
Aubrey
Alcohol reacts with a carboxylic acid
Texas
and the reaction is catalysed by sulphuric acid
Vhulenda
an athlete with a mass of 70kg runs at a velocity of 45km . determine the athlete's momentum
Lesedi Reply
Is that a velocity or something else
msawenkosi
45km/h i guess
Texas
Change to m/s
Texas
45km/h = 12.5 m/s p=mv =70×12.5 =875 kg.m/s
Thato
what are the measures of the rates of reaction
Lesego Reply
Volume Concentration Temperature Pressure Surface Area
Thato
the principle of superposition of waves
Sfundo Reply
what is work
Kool Reply
is this a group chat
Nobuhle Reply
Hey can y'all define newton's 2nd law
mthebzification
If a resultant force act on an object...the object will accelerate in the direction of a resultant force,the acceleration of the object is directly proportional to the net force and inversely proportional to the mass of the object
mosa
how do you calculate tension force
Bulumko
use the formula Fnet=ma if there is tension connecting two objects
Sboniso
to calculate Tension, usually calculate acceleration first Draw separate free body diagrams for each body. Apply Fnet = ma to calculate Tension
Kevin
Hi people
Paul
how does temperature affect the equilibrium position
Blessing Reply
an increased temperature increases the average kinetic energy thus in turn increases the number of effective collisions........
Lwando
so...which reaction is favored between endothermic and exothermic .when temperature is increased..?
Blessing
exothermic reaction because energy is realised to the surroundings as heat and light energy ....graphical so much energy is realised as reactants to form product and because temperature is high rate of reaction is fast which means there is a successful collision
Code
INTEMENDO - INCREASE IN TEMPERATURE FAVOURS ENDOTHERMIC DETEMEXO - DECREASE IN TEMPERATURE FAVOURS EXOTHERMIC
Thato
an object will continue in a state of rest unless it is acted upon an unbalanced force
Junior Reply
Newton's Law 1
Code
First Newton's Law
Azola
Newton's first law
Surprise
newton first law
Thinavhuyo
Newton's first law
Blessing
when pressure is increased what happen to volume
Siphelo Reply
decreases
Code
care to explain?
Mpati
if pressure is applied to a pistol , the volume will decrease and particles will collide more frequently with the wall of a container .Each time they collide with the wall they exert a force on them .More collision means more force and the pressure will increase , that Boyle's Law
Code
Because the volume has decreased , the particle will collide more frequently with the wall of a container and each time they collide with the wall of a container they exert a force on them.More collision means more force so the pressure will increase , that Boyle's Law
Code
what is the difference between momentum and a change in momentum?
Chavonne Reply
Change in momentum is the impulse of the object
Rachel
Momentum is a vector quantity equal to the product of the mass of the particle and its velocity
Mmola
How to name a branched molecule from right or left?
Vadin Reply
What's Free Fall
Senzo Reply
Free Fall means there is no acting force on that object.
Dingaletu
only gravitational force
Dingaletu
no external force acting on an object
Sphiwe
by only force of gravite
Sello
but gravitational force
Sphiwe
true
Lucky
a motion in which the only force acting is gravitational force
Blessing
and an object experiencing free fall is referred as a projectile
Blessing
Do polymers form restrictedly only if compound is saturated, only?
milani 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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