How to calculate Carbonate, Bicarbonate and Hydroxide Alkalinity?
Alkalinity is the ability of water to withstand acidic changes in pH; in other words, alkalinity is the ability of water to neutralize acid.
A water body with a high amount of alkalinity (as opposed to an alkaline water body) has more calcium carbonate, CaCO3, which can reduce the acidity of the water. As a result, alkalinity determines how much acid may be added to a water body without causing a significant pH shift.
Fish and other aquatic life require a pH range of 6.0 to 9.0, and alkalinity protects live species that require a specific pH range by buffering abrupt pH fluctuations. Acid rain and other acid pollutants will be buffered by higher alkalinity levels in surface water, reducing pH shifts that are hazardous to aquatic life. It is also crucial in wastewater and drinking water treatment because it affects cleansing processes such as anaerobic digestion. If the alkalinity level in the water is higher than the natural level of alkalinity in the soil, it may be inappropriate for irrigation.
Water hardness and alkalinity
Alkalinity and water hardness are comparable in that they both arise from natural sources. On its path to rivers and lakes, water passes through rocks (picking up minerals in the process). One half of the molecule contains calcium or magnesium (the "hardness"), while the other half is carbonate when limestone and dolomite dissolve in water (the "alkalinity"). This means that the hardness and alkalinity of the water at a given location will be quite comparable. They are, however, completely distinct metrics with very different implications.
Calculation of alkalinity
Alkalinity is represented by a high pH and refers to a substance's ability to take a proton.
Alkalinity may be calculated using a variety of ways:
The one utilized here employs the dissociation of carbonic acid, H2CO3
[Alk.] = + 2[CO2-3] + [OH-] - [H+],
Where Bicarbonate, carbonate, hydroxide, and hydrogen are the component ions, respectively.In such a case, the ion concentrations in g/m3 are obtained.
Step 1. Converting g/m3 to eq./m3
Divide the raw bicarbonate, carbonate, and hydroxide concentrations by their EW values, which are determined from their molecular masses. This gives you the eq./m3 concentrations of these ions. These are 61, 30 and 17 points, respectively.
Consider the following scenario:
[HCO3-] = 488 g/m3, [CO2-3] = 20 g/m3,
[OH-] = 0.17 g/m3, [CO2-3] = 20 g/m3,
[OH-] = 0.17 g/m3,
Divide by 61, 30 and 17 to get {8, 0.67, and 0.01 eq./m3}.
Step 2: Look for [H+]
This step needs knowledge of the constant [OH-][H+] = Kw = 10-14.
To convert the concentration to units appropriate for this step, divide the computed value of [OH-] from Step 1={0.01 ÷ 1,000 = 10-5} in this situation.
As a result, [H+] = 10-14/ 10-5 = 10-9.
Step 3: Take [H+] and multiply it by 1,000.
The units are reset to eq./m3.
1,000 *10-9 equals 10-6.
Step 4: Calculate the alkalinity
[Alk.]= 8 + 0.67 + 0.01 - 10-6= 8.68 eq./L
Bonus Step: To find the alkalinity in terms of mg/L of calcium carbonate, a commonly used measure of alkalinity, {multiply by 50,000}:
8.68 eq. /L × 50,000 mg/eq. = 434 mg/L as CaCO3
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