BVB College pH
Richard Bremmer
What is pH?
pH stands for: potential Hydrogenii
pH is a parameter for the concentration of H+ ions (hydrogen ions) in watery solutions
pH is expressed in a negative logarithm
• pH 3 = 10-3 mol H+
• pH 7 = 10-7 mol H+
(=0.001 mol/l)
(=0.0000001 mol/l)
pH and the concentration of H+ and OHpH and concentration acid (H+) and hydroxide (OH-)
pH (log10)
H+ (mol/l)
OH- (mol/l)
0
1 100
0,00000000000001 10-14
1
0,1 10-1
0,0000000000001 10-13
2
0,01 10-2
0,000000000001 10-12
3
0,001 10-3
0,00000000001 10-11
4
0,0001 10-4
0,0000000001 10-10
5
0,00001 10-5
0,000000001 10-9
6
0,000001 10-6
0,00000001 10-8
7
0,0000001 10-7
0,0000001 10-7
8
0,00000001 10-8
0,000001 10-6
9
0,000000001 10-9
0,00001 10-5
10
0,0000000001 10-10
0,0001 10-4
11
0,00000000001 10-11
0,001 10-3
12
0,000000000001 10-12
0,01 10-2
13
0,0000000000001 10-13
0,1 10-1
14
0,00000000000001 10-14
1 100
Acid
 pH neutral
Basic
What does the pH value tell us?
The higher the concentration H+ ions, the lower the pH
pH =
H+ = Acid
pH =
H+ = Basic
What is pH?
How to interpret the pH scale?
mmol H+ per liter
120
100
80
60
40
[H+]
20
0
1
3
5
pH
7
What is pH?
How to interpret the pH scale?
mmol H+ per liter
0,120
0,100
0,080
0,060
0,040
[H+]
0,020
0,000
4
5
6
pH
7
pH in substrates
7
How do we measure pH in substrates?
In the Netherlands we measure the pH level in the 1:1,5 extraction method:
The substrate is brought in slurry with demiwater.
1 part substrate = 120 cc
1,5 part demiwater = 180 cc
We call this a ‘watery solution’
8
Measuring pH in slurry
H+
OHpeat particle
4,0
Water
4,0
Some H+ is tied
to peat
particles and
will not be
measured
Slurry (1:1,5)
9
Different measurements
Measurement
Cocopeat RHP
Block peat fraction
2
Press soil
Direct into the soil
5,19
3,58
4,85
Squeeze out
moisture
5,43
3,49
5,01
1:1,5 in slurrie
6,18
3,93
5,33
In filtrate
5,70
5,26
5,02
10
Acid in the complex: what is the effect?
Lime dosage and obtained pH in blackpeat
Lime
dosage (g/l)
Achieved pH
Solved [H+]
mmol/l
Addition
[CO32-]
mmol/l
Neutralized [H+] mmol/l
0
3,1
0,794
0
0
1
4,3
0,050
10
20
2
4,8
0,016
20
40
3
5,1
0,008
30
60
4
5,3
0,005
40
80
5
5,5
0,003
50
100
Despite the lime dosage, there is only a small decrease of the H+
concentration in the watery solution.
Nevertheless, all the lime is used up; Not all neutralized H+ is noticeable in the
watery solution. Liming will also free a lot of the H+ from the peat.
Source RHP
11
H+ in organic compounds
Humic acid
Fulvic acid
12
Organic compounds act as a weak acid
H+
pH increases, f.i. caused by
liming
weak acid reacts by
setting free H+
13
Organic compounds act as a ‘weak acid’
H+
pH in solution decreases, f.i.
caused by cation uptake by
plants
Weak acid reacts by fixing
H+
14
Buffered H+ has significant influence
How to measure this?
4,0
H+
OH-
5,0
A known quantity of OH- is added. Part of the acid will be
neutralized
pH buffer = OH- quantity that is required for pH change of 1
point
15
Buffered H+ has significant influence
5,0
H+
OH-
4,0
A known quantity H+ is added.
pH will decrease and part of the H+ will be absorbed
pH buffer = H+ quantity that is required for pH change of 1 point.
16
pH buffer
•
pH buffer is the quantity of H+ that :
• is absorbed when pH increases
• is released when pH decreases
•
pH buffer is expressed in: Meq H+ /pH point
17
Example of peat response curve
14
12
10
pH
8
6
4
2
0
-60
-50
-40
Acid (H+)
-30
-20
-10
0
10
20
40
50
60
Base (OH-)
meq/l
Baltic milled peat
30
Pure acid/base
Source RHP
18
Example of peat response curve
7
+21 meq OH- / l
6
Demiwater
5
pH
4
pH changes from
3,8 to 5,0
3
2
= 17,5 meq / pH point
1
0
-50
-40
Acid (H+)
-30
-20
-10
0
10
20
30
40
50
Base(OH-)
meq/l
Baltic milled peat
Source RHP
19
Response curve of different peat qualities and origins
7
6
5
pH
4
3
2
1
0
-50
-40
Zuur (H+)
-30
-20
-10
0
10
20
30
40
50
meq/l
Freesturf
loog Baltisch
(OH-)
Source RHP
20
Response curve of different raw materials
pH
11
10
9
8
7
6
5
4
3
2
1
0
-60
-50
-40
-30
-20
-10
Acid(H+)
Baltic milled peat
0
10
20
30
Bark
50
Base (OH-)
meq/l
Cocopeat
40
Wood fibre
Source RHP
21
pH buffer of raw materials
In RHP research determined pH buffer of different raw
materials in the pH range 4 – 6,5. These are indicative
values.
Raw material
pH buffer (meq/liter product)
Milled peat Baltic
23
Milled peat Irish
19
Block peat Irish
17
Fine Baltic
21
Blackpeat German
24
Blackpeat Baltic
24
Cocopeat
7
Woodfibre
4
Bark
15
Source RHP
22
Important to remember
•
The pH of a substrate is actually the pH of the
soil moisture of this substrate.
•
•
Organic raw materials have a pH buffer
 pH changes are reduced
pH buffer of non-peat raw materials can differ a lot from peat.
23
Is your pH stable?
More information about
BVB College pH
at the stand of BVB Substrates
24