Suppose a powerful battery is connected between a pair of...

Suppose a powerful battery is connected between a pair of inert graphite electrodes dipped into a pot of molten aluminum oxide ($Al_2O_3$) (see sketch at right). The battery makes a current of electrons flow in the directions shown by the arrows in the sketch. Note: Group 1A and Group 2A metals all melt at temperatures lower than their salts. Which electrode is the anode? A B Write a balanced equation for the half-reaction that takes place at electrode A. Write a balanced equation for the overall reaction.

Transcript

00:01 In this question we are given a setup and according to the setup we are supposed to find according to the first subpart we are supposed to find the anode.

00:12 Now we are given a setup in this.

00:14 Ok we are given a setup.

00:16 Now we have to use this setup to find which is anode.

00:21 Now in this question if you see we can identify that what is anode.

00:27 At anode what happens? basically we have learnt that at anode oxidation takes place and in this setup oxidation takes place for aluminium.

00:37 If you see aluminium in its metal state gets converted into aluminium 3 plus ion.

00:44 So here oxidation means what? oxidation is nothing but it is losing electrons.

00:51 Whenever an element loses electrons we say that it is getting oxidized or oxidation is taking place with it.

00:57 So aluminium lost 3 electrons so their oxidation took place.

01:02 So aluminium oxidation took place where? it took place at electrode a.

01:09 If you check at electrode a, aluminium oxidation took place which means that is the anode.

01:18 Which means that is the anode.

01:21 That is the electrode where oxidation took place.

01:23 That is anode.

01:25 Oxidation happened because aluminium got converted into aluminium 3 plus ion.

01:30 So it has lost electrons so oxidation took place at electrode a and hence it is anode.

01:36 Next we are asked to find the balanced equation for the half reaction that takes place at electrode a.

01:40 As told earlier at electrode a what happens? at electrode a if you see, electrode a aluminium gets converted into aluminium 3 plus ion.

01:50 Now in this question we are given that al2o3 is found.

01:55 Now al2o3 means what? al2o3 means we have 2 aluminiums, 3 oxygens we have.

02:02 So if these 2 aluminiums, what is the oxidation state usually of aluminium? it is plus 3 right? this is plus 3.

02:09 So total 6 electrons plus and here 3 of oxygen.

02:13 Oxygen is 2 minus.

02:15 So 3 o2 minus and 2 al3 plus oxygen 3 2's are 6.

02:19 So here we have minus 6 electrons.

02:22 Here we have plus 6 electrons.

02:23 That is why this thing is balanced.

02:26 That is why this thing is balanced and al2o3 is found.

02:31 So in this particular setup given to us there is exchange of 6 electrons at a time.

02:37 So if i have to write the half reaction of aluminium what i have to do is i have to get 6 electrons.

02:43 I have to get 6 electrons out.

02:45 So for that aluminium is there in the solid state.

02:48 It is getting converted into aluminium 3 plus.

02:50 We know that.

02:51 But here i want 6 electrons.

02:54 Now if i have to get 6 electrons, obviously i want 2 aluminiums and if 2 aluminiums should be there over here.

03:01 According to the formula of this only you can understand that 2 aluminiums i should get.

03:06 So 2 aluminiums if i have to get over here, there also there should be 2 aluminiums right? so this is the balanced half cell, anode at electrode a what happens half reaction this is.

03:20 This is the half reaction at electrode a.

03:26 Third we are asked to write the balanced equation for the overall reaction...

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