Potassium
Hydroxide
Physical and Chemical Properties |
|
MSDS
Material safety data for dry potassium hydroxide in Adobe .PDF format.
|
|
Physical
Constants
|
| Chemical
Name |
Potassium
Hydroxide |
| Chemical Formula |
KOH |
| Molecular
Weight |
56.1 |
| Crystalline
Form |
Rhombic |
| Specific Gravity |
2.044 |
| Melting Point |
380°C
(716°F) |
| Boiling Point
@ 760 mm Hg pressure |
1,320°C
(2,480°F) |
| Heat of Fusion |
28.6 cal/g |
| Heat of Solution
@ 18°C |
+13.29 Kg-cal
per 250 moles H2O |
|
Solubility
in Various Solvents
|
| Cold Water
@ 0°C |
97 grams per
100 mL water |
| Hot Water
@ 100°C |
178 grams
per 100 mL water |
| Organic Solvents |
Very soluble
in alcohol and ether |
| Inorganic
Solvents |
Insoluble
in NH3 |
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|
Chemical
Reactions
|
| Moisture |
KOH
is deliquescent and absorbs moisture from the air until it is dissolved.
Heat is evolved during the dissolving process. |
| pH |
KOH
solutions are strongly alkaline and have a pH value greater than 12. |
| Carbon
Dioxide |
In
the presence of moisture, KOH reacts with CO2 from the air to
form K2CO3 and KHCO3. |
| Animal
and Plant Fibers |
All
living tissues, especially animal fibers such as wool, leather, silk and
human skin are rapidly dissolved by KOH and thus destroyed. Plant fibers
like cotton and rubber are less readily attacked. |
| Heavy
Organic Compounds |
In
order to make heavy organic compounds soluble in water, parts of the KOH
molecule are added by means of replacement and saponification reactions. |
| Inorganic
Compounds |
KOH
reacts with inorganic acids and acidic anhydrides to form potassium salts.
With metals it forms insoluble hydroxides. |
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|
Dilution
of Liquid Caustic Potash
|
The
following problems make use of the fundamental equations:
DENSITY=WEIGHT/VOLUME
Concentration 1 x Volume 1 = Concentration 2 x Volume 2 |
| EXAMPLE
1: Dissolving Solid Forms of KOH |
Problem
What amount of ASHTA flake caustic potash (90% KOH) and what amount of water
must be added in order to obtain 20% KOH solution? |
Solution
Refer to the Dilution Chart below since 90% KOH and water (0% KOH) are involved,
use line A, which connects these two points. Follow the 20% line vertically
until it intersects line A. Read horizontally left and right from the point
of intersection. 22 lbs. of strong solution (90% KOH) must e added to 78
lbs. (9.38 gallons) of dilute solution (water) in order to obtain a 20%
KOH solution. Pounds of water can be changed to gallons by dividing by 8.32
lb./gal. |
| EXAMPLE
2: Diluting a KOH Solution |
Problem
How many gallons of water must be added to 2,000 gallons of liquid caustic
potash in order to obtain a 29% KOH solution? The KOH is found to have a
specific gravity of 1.45 at 20°C. |
Solution
Refer to the Specific Gravities Table and find that a 20°C caustic potash
solution with a specific gravity of 1.45 contains 45% KOH by weight. On
the Dilution Chart, follow the 29% line vertically until it intersects line
B and read horizontally left and right from the point of intersection. 35.6
lbs. of water must be added to 64.4 lbs. of 45% KOH. Divide each number
by its density (in lbs./gal.) to change from pounds to gallons and then
divide the resulting numbers to obtain the number of gallons of water to
be added to each gallon of 45% KOH. |
35.6/8.32=4.28;
64.4/12.09=5.33
4.28/5.33=0.803 gal.water/gal.45% KOH |
| EXAMPLE
3: Determining the Final Volume of a KOH Solution |
Problem
After dilution, what will be the final volume at 20°C of the KOH solution
in example 2? |
Solution
Due to the chemical nature of caustic potash, shrinkage occurs when KOH
solutions are diluted with water so that the final volume is always less
tan expected. The exact final volume may be calculated as follows: Determine
the weight of the original (45% KOH) solution and the weight of water added
by multiplying the number of gallons by the density (in lb./gal.). Add the
weights together and divide by the density (in lb./gal.) of the diluted
(29% KOH) solution. |
(200
x 12.09) + (1606 x 8.32) = 37542 lb.
(37542 lb.) / (10.63 lb./gal.) = 3532 gal. of 29% solution
The final volume is actually 3532 gallons compared to the expected volume
of 3606 gallons. |
| EXAMPLE
4: Strengthening a KOH Solution |
Problem
How many gallons of 45% KOH must be added to 1,000 gallons of 25% KOH in
order to obtain a 30% KOH solution at 20°C? |
Solution
Follow the 30% line on the Dilution Chart vertically until it intersects
line C. Read horizontally left and right from the point of intersection.
25 lbs. of 45% must be added to 75 lbs. of 25% in order to make a 30% KOH
solution. Divide each number by its density (in lb./gal.) to change from
pounds to gallons. Densities at 20°C can be obtained from chart 2. Divide
the resulting numbers to obtain the number of gallons of 45% to be added
to each gallon of 25%. |
25/12.09=2.07;
75/10.12=7.41
2.07/7.41=0.279 gal.45% KOH/gal.25% KOH
Since 1,000 gallons of 25% KOH are to be strengthened, multiply 0.279 by
1,000. 279 gallons of 45% KOH must be added to 1,000 gallons of 25% KOH
in order to obtain a 30% solution. |
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|
Densities
and Concentrations
of aqueous caustic potash solutions
at 20°C (68°F)
|
| |
Density
of KOH Solutions
|
Amount
of KOH in Solution
|
|
%
KOH
(by weight)
|
Specific
Gravity
|
Pounds
per Gallon
|
Degrees
Baumé
|
Degrees
Twaddell
|
Actual
Concentrations
(100% KOH basis)
|
International
Caustic Potash
(90% KOH basis)
|
|
2
|
1.01623
|
8.46
|
2.3
|
3.2
|
0.17
|
0.19
|
|
4
|
1.03437
|
8.61
|
4.8
|
6.8
|
0.34
|
0.38
|
|
6
|
1.05262
|
8.76
|
7.3
|
10.5
|
0.53
|
0.59
|
|
8
|
1.07106
|
8.91
|
9.6
|
14.2
|
0.71
|
0.79
|
|
10
|
1.08970
|
9.07
|
11.9
|
17.9
|
0.91
|
1.01
|
|
12
|
1.10855
|
9.22
|
14.2
|
21.7
|
0.91
|
1.01
|
|
14
|
1.12763
|
9.38
|
16.4
|
25.5
|
1.31
|
1.46
|
|
16
|
1.14694
|
9.54
|
18.6
|
29.4
|
1.53
|
1.70
|
|
18
|
1.16645
|
9.71
|
20.7
|
33.3
|
1.75
|
1.94
|
|
20
|
1.18617
|
9.87
|
22.8
|
37.2
|
1.97
|
2.19
|
|
22
|
1.20600
|
10.04
|
24.8
|
41.2
|
2.21
|
2.46
|
|
24
|
1.22614
|
10.20
|
26.8
|
45.2
|
2.45
|
2.72
|
|
26
|
1.24650
|
10.37
|
28.7
|
49.3
|
2.70
|
3.00
|
|
28
|
1.26712
|
10.54
|
30.6
|
53.4
|
2.95
|
3.28
|
|
30
|
1.28799
|
10.72
|
32.4
|
57.6
|
3.22
|
3.58
|
|
32
|
1.30913
|
10.89
|
34.2
|
61.8
|
3.48
|
3.87
|
|
34
|
1.33053
|
11.07
|
36.0
|
66.0
|
3.76
|
4.18
|
|
36
|
1.35219
|
11.25
|
37.8
|
70.4
|
4.05
|
4.50
|
|
38
|
1.37413
|
11.43
|
39.5
|
74.8
|
4.34
|
4.82
|
|
40
|
1.39634
|
11.62
|
41.2
|
79.3
|
4.65
|
5.17
|
|
42
|
1.4188
|
11.80
|
42.8
|
83.8
|
4.96
|
5.51
|
|
44
|
1.44164
|
11.99
|
44.4
|
88.3
|
5.28
|
5.88
|
|
45
|
1.45314
|
12.09
|
45.2
|
90.6
|
5.44
|
6.04
|
|
46
|
1.46477
|
12.19
|
46.0
|
92.9
|
5.61
|
6.23
|
|
48
|
1.48820
|
12.38
|
47.6
|
97.6
|
5.94
|
6.60
|
|
50
|
1.51211
|
12.58
|
49.1
|
102.4
|
6.29
|
6.99
|
|
52
|
1.53632
|
12.78
|
50.6
|
107.3
|
6.65
|
7.39
|
Source: Data
in columns 1 and 2 are taken from Akerloff and Bender, J. Am. Chem. Soc.,
63: 1088 (1941).
The remaining columns are calculated from the following formulas:
Specific Gravity = (density KOH solution) / (density H2O) = (density
KOH in lbs./gal. @ 20°C) / (8.321)
°Be. = 145 - (145 / specific gravity)
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|
Boiling
Points
of aqueous caustic potash
solutions
|
|
Temp.
(°C)
|
%
KOH
(by weight)
|
Temp.
(°C)
|
%
KOH
(by weight)
|
|
100
|
0.0
|
230
|
70.67
|
|
110
|
25.65
|
240
|
72.46
|
|
120
|
36.51
|
250
|
74.07
|
|
130
|
43.42
|
260
|
75.76
|
|
140
|
48.05
|
270
|
77.52
|
|
150
|
51.57
|
280
|
79.05
|
|
160
|
54.88
|
290
|
80.32
|
|
170
|
57.8
|
300
|
81.63
|
|
180
|
60.42
|
310
|
82.99
|
|
190
|
62.73
|
320
|
84.03
|
|
200
|
64.93
|
330
|
85.11
|
|
210
|
66.89
|
340
|
86.16
|
|
220
|
68.73
|
|
|
Back
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|
Solubility
of caustic potash in
water
|
|
Temperature
(°C)
|
%
KOH (by weight)
|
Solid
Phase
|
|
-2.2
|
3.6
|
Ice
|
|
-20.7
|
18.4
|
Ice
|
|
-65.2
|
30.8
|
Ice
|
|
-36.2
|
26.6
|
KOH
· 4H2O
|
|
-32.7
|
43.8
|
KOH
· 4H2O
|
|
-33
|
44.4
|
KOH
· 4H2O + KOH · 2H2O
|
|
-23.2
|
45.9
|
KOH
· 2H2O
|
|
0
|
49.2
|
KOH
· 2H2O
|
|
10
|
50.7
|
KOH
· 2H2O
|
|
15
|
51.7
|
KOH
· 2H2O
|
|
20
|
52.8
|
KOH
· 2H2O
|
|
30
|
55.76
|
KOH
· 2H2O
|
|
32.5
|
57.44
|
KOH
· 2H2O + KOH · H2O
|
|
50
|
58.33
|
KOH
· 2H2O + KOH · H2O
|
|
100
|
64.03
|
KOH
· 2H2O
|
|
125
|
68.06
|
KOH
· 2H2O
|
|
143
|
75.73
|
KOH
· 2H2O
|
Back
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|
Specific
Gravities
of aqueous potash solutions at various temperatures
and concentrations
|
| % KOH (by
wt.) |
32°F
0°C |
50°F
10°C |
68°F
20°C |
86°F
30°C |
104°F
40°C |
122°F
50°C |
140°F
60°C |
158°F
70°C |
| 0 |
0.99982 |
0.99948 |
0.99800 |
0.99553 |
0.99219 |
0.98809 |
0.98330 |
0.97789 |
| 2 |
1.01927 |
1.01822 |
1.01623 |
1.01341 |
1.00985 |
1.00562 |
1.00076 |
0.99529 |
| 4 |
1.03849 |
1.03681 |
1.03437 |
1.03124 |
1.02749 |
1.02315 |
1.01822 |
1.01269 |
| 6 |
1.05773 |
1.05548 |
1.05262 |
1.04922 |
1.04528 |
1.04083 |
1.03583 |
1.03026 |
| 8 |
1.07706 |
1.07429 |
1.07106 |
1.06739 |
1.06329 |
1.05872 |
1.05366 |
1.04804 |
| 10 |
1.09650 |
1.09327 |
1.08970 |
1.08579 |
1.08153 |
1.07686 |
1.07174 |
1.06607 |
| 12 |
1.11607 |
1.11243 |
1.10855 |
1.10443 |
1.10002 |
1.09526 |
1.09008 |
1.08437 |
| 14 |
1.13576 |
1.13177 |
1.12763 |
1.12332 |
1.11877 |
1.11392 |
1.10868 |
1.10293 |
| 16 |
1.15557 |
1.15130 |
1.14694 |
1.14245 |
1.13779 |
1.13285 |
1.12756 |
1.12176 |
| 18 |
1.17546 |
1.17098 |
1.16645 |
1.16183 |
1.15706 |
1.15205 |
1.14670 |
1.14087 |
| 20 |
1.19542 |
1.19082 |
1.18617 |
1.18145 |
1.17659 |
1.17151 |
1.16610 |
1.16024 |
| 22 |
1.21532 |
1.21069 |
1.20600 |
1.20122 |
1.19630 |
1.19116 |
1.18570 |
1.17981 |
| 24 |
1.23575 |
1.23094 |
1.22614 |
1.22132 |
1.21635 |
1.21115 |
1.20565 |
1.19973 |
| 26 |
1.25642 |
1.25145 |
1.24650 |
1.24154 |
1.23651 |
1.23128 |
1.22576 |
1.21982 |
| 28 |
1.27730 |
1.27219 |
1.26712 |
1.26204 |
1.25691 |
1.25159 |
1.24602 |
1.24006 |
| 30 |
1.29840 |
1.29318 |
1.28799 |
1.28280 |
1.27758 |
1.27217 |
1.26653 |
1.26054 |
| 32 |
1.31973 |
1.31442 |
1.30913 |
1.30384 |
1.29852 |
1.29302 |
1.28733 |
1.28129 |
| 34 |
1.34132 |
1.33591 |
1.33053 |
1.32514 |
1.31974 |
1.31416 |
1.30840 |
1.30232 |
| 36 |
1.36314 |
1.35766 |
1.35219 |
1.34672 |
1.34124 |
1.33558 |
1.32976 |
1.32364 |
| 38 |
1.38524 |
1.37969 |
1.37413 |
1.36857 |
1.36303 |
1.35729 |
1.35141 |
1.34524 |
| 40 |
1.40765 |
1.40199 |
1.39634 |
1.39071 |
1.38510 |
1.37930 |
1.37335 |
1.36713 |
| 42 |
1.43037 |
1.42459 |
1.41884 |
1.41313 |
1.40747 |
1.40160 |
1.39560 |
1.38932 |
| 44 |
1.45347 |
1.44751 |
1.44164 |
1.43585 |
1.43015 |
1.42422 |
1.41817 |
1.41182 |
| 46 |
1.47700 |
1.47079 |
1.46477 |
1.45889 |
1.45315 |
1.44718 |
1.44108 |
1.43465 |
| 48 |
1.50097 |
1.49442 |
1.48820 |
1.48222 |
1.47645 |
1.47045 |
1.46431 |
1.45779 |
| 50 |
1.52565 |
1.51861 |
1.51211 |
1.50600 |
1.50022 |
1.49419 |
1.48802 |
1.48139 |
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Conversion
Tables
| The
conversion factors below are calculated on a basis of 100% purity. To
convert compound A into an equivalent amount of compound B, multiply by
the A to B factor. To convert compound B into compound A, multiply by
the B to A factor. |
|
Compound
A
|
Compound
B
|
A
to B
|
B
to A
|
|
K
KOH
K2CO3
KCl
K2SO4
|
K2O
|
1.205
0.840
0.682
0.632
0.541
|
0.831
1.191
1.467
1.583
1.850
|
|
K2CO3
KHCO3
|
CO2
|
0.318
0.220
|
3.141
4.545
|
|
K2CO3
|
KOH
|
0.812
|
1.232
|
|
K2SO4
|
SO4=
|
0.551
|
1.814
|
|
Cl-
K2SO4
KNO3
|
KCl
|
2.103
0.856
0.737
|
0.479
1.169
1.356
|
Conversion
Factor A to B = (Equivalent weight B) / (Equivalent weight A)
Conversion Factor B to A = 1 / (Conversion Factor A to B) |
|
Equivalent
Conductance
of caustic potash
solutions
|
|
°C
|
°F
|
|
Reference
|
|
18
|
64.4
|
238.7
|
(40)
|
|
18
|
64.4
|
239.0
|
(3)
|
|
25
|
77.0
|
274.9
|
(24)
|
|
25
|
77.0
|
274.9
|
(16)(17)
|
|
25
|
77.0
|
283.9
|
(33)
|
|
25
|
77.0
|
285.46
|
(32)
|
|
90
|
194.0
|
599.0
|
(8)
|
|
Heat
of Neutralization
of caustic potash
and caustic soda solutions at 20°C
|
|
Mol
Acid / 100 Mol H2O
|
Mol
KOH / 100 Mols H2O
(Calories)
|
Mol
NaOH / 100 Mols H2O
(Calories)
|
|
HCl
|
14014
|
13895
|
|
HBr
|
13988
|
13843
|
|
HI
|
13915
|
13779
|
|
HNO3
|
14086
|
13836
|
|
Heat
of Solution
|
|
°C
|
°F
|
Mol
of Water
per Mol KOH
|
Heat
of Solution
kcal/mol
|
B.T.U.
per lb. KOH
|
Reference
|
|
11.4
|
52.5
|
260
|
12.46
|
399.9
|
(5)
|
|
18.0
|
64.4
|
250
|
13.29
|
426.5
|
(62)
|
|
100
|
212
|
260
|
16.8
|
539.2
|
(6)
|
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