Alkalinity
Introduction
(from Arabic "al-qalī"[1]) is the capacity of water to resist acidification.[2] It should not be confused
with basicity which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer
solution composed of weak acids and their conjugate bases. It is measured by titrating the solution
with an acid such as HCl until its pH changes abruptly, or it reaches a known endpoint where that
happens. Alkalinity is expressed in units of concentration, such as meq/L (mill equivalents per litter),
μeq/kg (micro equivalents per kilogram), or mg/L CaCO3 (milligrams per liter calcium carbonate).[3]
Each of these measurements corresponds to an amount of acid added as a titrant.
Although alkalinity is primarily a term used by oceanographers,[3] it is also used by hydrologists to
describe temporary hardness. Moreover, measuring alkalinity is important in determining a stream's
ability to neutralize acidic pollution from rainfall or wastewater. It is one of the best measures of the
sensitivity of the stream to acid inputs.[4] There can be long-term changes in the alkalinity of
streams and rivers in response to human disturbances such as acid rain generated by SOx and NOx
emissions.[5]
Objective
-To determined the Alkalinity of specific volume liquid quantity.
- Calculate the total Alkalinity
Theory
Alkalinity is a measure of the capability of water to absorb H+ ions without significant change of pH.
In other words, alkalinity is a measure of the acid buffering capacity of water.
The determination of alkalinity of water is necessary for controlling the corrosion
- We can calculate Alkalinity using the following equation
A∗N∗EWCACO 3∗10 3
CaCo 3 mg/l=
V
Where …
A = The volume of titration solution ( H2SO4 )
N = Normality of titration solution H2SO4 ( 0.02).
EWCaCO3 = 50g
V = The volume of the sample (ml)
-Also the total Alkalinity can be calculated using the following equation
Total Alkalinity = Ph.Ph alkalinity + M.O Alkalinity
Tools and reagents
1- Burette (100ml) 2- pipette
3-conical flask 4- beakers
5-H2SO4 (N = 0.02) 6- Phenolphthalein (Ph.Ph)
7- Methyl orange (M.O) 8- samples of water
Procedures
1- fill the burette titration solution H2So4 ( 0.02 N) using the funnel.
2- Take a specific volume for the water sample (50 ml.)
3- Add a little quantity of phenolphthalein (ph.ph) , if the color changed to
Pink then there exist strong alkalinity in the sample ( 8.3 < PH < 10 ).
4-Start titration until back to color less water then calculates the value of ph.ph alkalinity.
5- Add methyl orange (M.O) we will observant the color change again
to orange or to red the change in the color depended on PH value.
6- Do titration again and find the methyl orange alkalinity .
7- Finally calculate the total alkalinity by adding the results ( ph.ph + M.O).
Calculations and Result
A∗N∗EWCACO 3∗10 3
as CaCo 3 mg/l=
V
Total Alkalinity = Ph.Ph alkalinity + M.O Alkalinity
For the first sample…
AH2SO4 = 8ml N = 0.02 Vsample = 50ml EWCaCO3= 50g
Ph.Ph Alkalinity = 0
Carbonate Alkalinity = (8 * 0.02 * 50 * 10^3) /50
= 160 mg/L as CaCO3
Total Alkalinity = 0 + 160
160 mg/L as CaCO3
Sample’s Sample’s Ph.Ph M.O Total Ph.ph M.O Total
Number volume alkalinity alkalinity AH2SO4 Alkalinity Alkalinity Alkalinity
(ml) AH2SO4 AH2SO4 (ml) (Mg/L) (Mg/L) as (mg/L) as
(ml) (ml) as CaCo3 CaCo3 CaCo3
1 50 0 8 8 0 160 160
2 50 21 6 27 420 120 540
3 50 0 0 0 0 0 0
4 50 4 7 11 80 140 220
5 50 8 9 17 160 180 340
Conclusion
The amount of Alkalinity Allowed to be in water is 80-200 mg/L for typical drinking water. Alkalinity
is basically dissolved minerals in the water that help neutralize the water we drink.
The Total Alkalinity
Sample’s as CaCO3 comment
Number ( mg/L)
1 160 Drinkable
2 540 Undrinkable
3 0 Undrinkable
(Acidic Sample)
4 220 Undrinkable
5 340 Undrinkable
