Omega PHB21, Руководство пользователя

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++ -
MA M A
+
K = aM * aA- / aMA (EQ-1)
+ + -
HCl H Cl
+ + -
CH COOH H CH COO
3 3
NaOH Na OH
+ + -
+ + -
NH OH NH OH
4 4
+ + -
HOH H OH
3.
PH Measurement
3
Stable chemical compounds, are electrically neutral when mixed with water.
In order to form a water solution, dismember in positive or negative charged particles.
These charged particles are called "i
”. When we apply differential potential in two electrodes immersed in a
+ +
solution, it is possible to verify that positive ions (H , Na and more) will migrate to the negative terminal, that is
- -
why we call them cations. The reverse happens with negative ions (OH , Cl and more) that will migrate to the
“ “
positive terminal and we call them anions. The ions freedom to migrate thru a solution is measured with
the solution
". Chemical compounds that produce conductive solutions are called
" ". Those that totally dissociate (strong acids, strong bases and salt) are called "
" .
The others whose dissociation is not big (acids and weak bases) are called " ". For an
hypotetical chemical compound "MA" that dissociates in cations and anions , the reaction can be written as:
ons
“Electrical Conductivity
lectrolytes Strong
Electrolytes
Weak Electrolytes
E
+ -
M A
+and -
The arrow indicates that exists a balance between MA not dissociated and the ions M and A dissociated.
The extension that this reaction moves to the right or left, varies from one compound to the other and with the solution
Temperature.
For a specific temperature, there is a relation between the ions activity and the non dissociated molecules, that can vary
between 0 up to 100%. This relation is called K Dissociation and it is expressed by the equation:
Where: K =
aM+ =
aA- =
aMA =
"K" .
CTE dissociation.
ions activity M+.
ions activity A-.
dissociated molecules activity MA.
For Chloridric acid, the is practically infinity, caused by the complete dissociation for ions and So it is a strong acid:
+ -
H Cl
On the other hand, Acetic acid has a low . Reacts as the following way: "K "
Few hydrogen ions result at the solution, so the acetic acid is an weak acid when the most present ion is the OH-, the
solution is alkaline.
The sodium hydroxide is totally dissociated, this is the reason for being a On the other hand the Ammonia
Hydroxide do not dissociate too much, this the reason for being a .
STRONG BASE .
WEAK BASE (NH OH)
4
As we can see, for both acids and bases the strength of a solution depends on the H+ or OH- ion numbers available that
depends not only on the compound concentration at the water, but also on the " "
Pure water dissociates for
Ions H+ and OH-, but it is very weak.
K dissociation.
The water molecules number dissociated is low, in comparison with the non dissociated, so we can consider as an
activity of HOH equal to 100%.