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Revision S7

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by

arie ramp

on 3 June 2018

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Transcript of Revision S7

So we have:
pH of....
What is the pH of a two molar solution of ammonia....?
What is the Kz of its conjucate base...
Remember .... Kw of water...
or pH + POH = 14
Calculate
Thank you!
Water Constant
Chatelier principle
So why is a solution of ammonia ... a basic solution.... When there is also the ammonium ion as the cojugate acid of the base... it is all about the base ...? or its opposite conjugate acid...
Lets have a look

Ammonia
pH + pOH = 14

in a table... Kz of pKz or pH and strength of solution
The ammonium cation is a positively charged ion with the chemical formula NH4+ It is formed by the protonation of ammonia (NH3).
Question what is the pH of a 2 molar solution of ammonia...
First write down the equation
Need of a constant of what ... Cb or Ca
Table of Ca and or Cb
Think which one is a larger number and think about a equilibrium which one is the largest number and which one will make a mark...?
Remember ... pH is an approximation within WATER ....we can't calculate all... ions involved...

The ammonium ion is generated when ammonia, a weak base, reacts with Brønsted acids (proton donors):
H+ + NH3 → NH4+
The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:
NH4+ + B− → HB + NH3
Thus, treatment of concentrated solutions of ammonium salts with strong base gives ammonia. When ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:
H2O + NH3 is in equilibrium with OH- + NH4+
The degree to which ammonia forms the ammonium ion depends on the pH of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high (the concentration of hydrogen ions is low), the equilibrium shifts to the left: the hydroxide ion abstracts a proton from the ammonium ion, generating ammonia.

Kb =
Kb = 1,8 x 10 Because
-5
Cb
Kb
= 2.0/1.8 X 10
-5
= 1,1 X 10
5
= 10
IS BIGGER THAN
2
OR
BIGGER THAN pKb > 2
=
and therefore we can state that the [NH ] is negligible in respect of the [NH ]
3
4
+
So we can say that the ammonia concentration is approximately the same as the original concentration of NH we added = 2.0 M
3
So fill this into your Kb equation .....
Kb =
products x products
reactants
this will give the OH- concentration [ OH-]
-log = pOH
pOH - 14 = pH.......?
11.78
Revision of acids and bases
S7 support lesson
dilutions and stoichiometry
how to make a buffer
pH and unloggen
strong and weak acids
conjugate base and acid
least acidic of alcohols
The strength of an acid is related to the stability of its conjugate base
the factors that stabilize negative charge
salts can act as acids
what is nitric acid?
neutralisation How many moles
names of acids and salts
Full transcript