Tip:
Highlight text to annotate it
X
(b) Water molecules can act as base.
c) Water molecules cannot be dissociated.
. (d) Water molecules are largely non-polar.
. This picture. So let me answer that.
I will show this diagram for purpose
to answer this problem, see some model is given to you.
this is just that,it will go into your memories,some diagram will help you to understand it.
ok, let us solve this problem.
auto protolysis of water shows ,this reaction is auto protolysis
because it is one water molecule,with a O two H,THIS IS ALSO ,O ,with two H,
off course need not forgot that there are two lone pairs,so, there are lone pairs.
so, one of the H is transffered ,so that three H happens to be on one molecule.
and only one H ,happens to be on another molecule.
one molecule which gain the proton is the base ,so, i can say that this molecule which gain the proton is base
and, another water molecule which lost the proton is an acid.
so, you find that one water acts as an acid,where as another water acts as a base.
so, it should act like both,both as an acid and as a base.
i hope it is clear?
go to next table,this is very important table
you should note down this table.
with this table you observe something very important.
what is it?auto protolysis changes with temperature
see,at zero degree,don't this Ph and all that because i haven't tought you that.
we can only study the Kw,this is .114*(10) to power -14
as i approach to 25 this 1.008,if i make this 8 insignificant then this 1*10 to power -14
as i increase the temperature we find that it is reaching upto 55.38*10 to power -14
it is again very interesting that at room temperature whatever dissociation happens
about 100 degree celcius,about 55 times of that or 50 times of that increases.
ok, why this happens?i told you that the reaction as an endothermic character.
then few people are just affected by this moles square deci meter minus 6,its very simple. H and OH ions are the two terms that you have in Kw.
which we write mole per lit. here also we write mole per lit. we all know that 1 L is actually deci meter cube,10 to power -3 deci meter cube or we can say ,1 deci meter is 10 cm
so, 10*10*10 that way, so this also mole divided by deci meter cube.so in fact you find that this mole square and deci meter raised to -6
so what is your understanding as the temperature increases Kw value also increases.
ok, next important point you should know is that.
if we compare the Kw of water with D2O,D2O is heavier isotope of water.where H heavier isotope is deuterium D.
THIS DIAGRAM explains you that,yhat D2O has higher values of Pka for any given value of temperature.
ok, you find that these are here as the temperature 10,20 25,30,40,50 degree temperature is increasing
ok, water's Pka value e.g. -logKw.that is also going in this direction.its gradually coming down.
because -log of increasing number should come down.
and here with D2O you find that at same value its amount is increased.
to explain these all data i will take the value of Ph ,Pka,
after explaining that i will come back here you will get it.
before that,heavy water which is called D2O,self ionizes lesser than normal water,oxygen forms a slightly stronger bond to deuterium.
because of larger mass of deuterium.
this i will explain,but before that let us go for PH and POH,
many people do not understand,how to take P values?
P is actually potential,power
so, let me explain you that,
look here,we come across in chemistry terms like PH,POH,PKa,PKb,PKw
and you can put anything which we like here.
these all have a general meaning,what is that?
these all have a general meaning,Ph has -log of H ion conc. but i can not say concentration but activity.
this is -log of OH- ion activity.
-log of Ka constant that is a number.
-log of Kb,-LOG OF Kw or -log of any quantity which is want to put as P.
so, -log of that quantity.
this table is telling you that,we have a notion,symbolic system where P is put just before the constant number of the value which you want to take on log scale.
now why we take these values,for this purpose i will tell you certain thing.its very important and listen.
probabily many of you know that ,but still i would to tell it .
let us do an exercise,you all listen to me carefully ,let us do an exercise.what is that exercise?
that we have two solution,let me draw a container, this is one container ,another container.it has some H ion concentration,it also has some H ion concentration.
its value is given 10 to the power -1, its value is given 10 to power -9.
let us say that this containers are labelled by A container and this is B container.
this A and B there are two container .and values are given
in 9th ,10 ,8,7,class we are tought been to draw bar diagrams ,bar graphs.
suppose one of your teacher in 8th class had given you exercise
suppose i had been your 8th class teacher i would have definately given you this exercise with some bets.
ok you take my car with you if you can really solve it.
this challenge is not been not been so far won by any student
which i tought in my entire carrier
So I am very sure that you are not be able to do that.ok
1 devided by,your goal is that you have to draw two bar graphs.
it seems that you are very enthusiastic to take the car,you are really looking,i am also very sure that you will not take the car.
your idea is that 1 devided by H ion should be plotted against A and B.
let us work,1 devided by H ion ,please for this A,1 DEVIDED H ion is 1devided 10 raised to power -1 that is 10.
1 by H ion for B solution is ,what is that?1 by 10 raised to power -9,that is 10 to power 9.
then there is a problem , i have to decide the scale.
i will say that when i move 1cm ,some magnitude is covered.
let me decide the magnitude covered is 10 or 100 or whatever it,you decide.
1 cm 10,ok so this 10 is drawn if i draw the height of this bar by 1 cm.
and to draw a bar i will devide this by 10.10 to power 9 by 10 that is 10 to power 8 cm.
ok,it seems its small number but let us see,10 to power 8 cm is 10 to power 5 m.
10 to power 5 m out of that i can take 1 KM.so 100 KM ,
plane flies at 10 KM ,a normal air plane,a passenger air plane flies at a height of about 10 KM.
WE HAVE TO GO time higher to that .
even getting a chopper or some or some thing to draw this graph
i think , its not possible for humans
haan,,,you people from mars you can do?
you can do any thing
do you it is a convenient to draw the graph?.
no, we have come to know that have to construct a very serious dead lock.
of drawing the or plotting the H ion concentration against their entity or against their name
we struct into a problem ,we are able to solve this.
such kind of problems are very easily solved with the help of log.we know that we most often face earth quakes all around us .some earth quakes are able to move our heirs.
we do not sense only news paper says there was earth quake and we all the time on what time it was ,we could not sense it?
but there are some earth quakes which even not leave news paper people to report that what happened?
earth quake varying in such large magnitudes
shaking the whole earth or just your heirs.
the variation in that large magnitude is also measured in log. scale.
what is that scale known as ?rector scale.very good, some G.K. is there .
so, geological people use rector scale and chemist people they can not just ignore it
so what is the idea?that instead of writing such problems let us take the -log. of such quantities.
now, a question comes why not positive log. is taken? the ans is that i devided water molecule ,i desociated water molecule,in very feeble amount.
very very small amount,if it is very small amount H ion concentration is most likely to have negative number,
and with this negative numbers if you have to handle further, you have to nullify this negative.and that is possible by taking a negative log.
of them.that's why this whole term have -ve,-ve,-ve in them.
how many people understood it?well,now,not only this but the next step is also very important
so we come to know that what is PH?PH is defined as -log of H ion
for those students who are serious enough i am going to give an exercise please be very care full and listen.
these are different solution 1,2,3,4,5,6,7,8,9,11,12, different solutions i am writing and all these solutions have different values of H ions.
so, let us put the values
ok, some values you can suggest me like this H ion value is 1M,0.1M,0.001M,0.0001M,10 TO power -5 M,10 TO POWER -7 MOLAR.........SO ON.THESE ALL ARE THE H ion values.like this.
obviously if i start to plot them here you can understand how these curve will be going.
so, it makes no sense if i directly go for a bar graph