An In-Depth Exploration: Chemical Analysis Unveiling Water Quality Dynamics

Estimating the amount of free chlorine in water: Chlorine is found in natural water because salt deposits dissolve in it, roads are salted to melt snow and ice, chemical industries dump waste water, wells run, garbage disposals, irrigation drainage, refuse leachates pollute the water, and seawater gets in along the coast. Chlorine ions can thus react with NH and various organic and inorganic compounds contained in water and wastewater. This will result in complex reactions by producing a combination of residual chlorine compounds. Both free chlorine and its compounds that exceed certain limits will be very dangerous for human consumption.

This can be analyzed using several different methods, some of which are:

  • Argentometric titrimetric method.
  • Iodometric titrimetric method.
  • Gravimetric determination.
  • Ion selective electrode method.
The following will discuss some of these methods:

1. Argentometric Titrimetric Method

Chloride can be easily and quickly determined through titration with AgNO solution, and by using K,CrO as an indicator, silver nitrate reacts with chloride in a neutral or slightly alkaline solution, which will then precipitate silver chloride as follows:
AgNO + NaCl = AgCl +NaNO

Potassium chromate also reacts with AgNO to give red-silver chromate. From the titration, we obtain:
KCrO, + 2CAgNO, Ag CrO, + 2KNO

Potassium chromate also reacts with AgNO to produce silver chromate red. From the titration, we obtain:
CrO, + 2CAgNO, Ag CrO, + 2KNO,

Red or pink (end point)
At the end point of the titration, if there is no more free chloride left, add one drop of AgNO titrant so that Ag Cro will be formed, resulting in a pink or red-colored


Set the pH of the 100-ml sample to 7 to 10 using H2SO, or NaOH. Then add 1 ml of H2O, 30% solution, and 1 ml of K2CrO solution, 5% (as an indicator). Stir evenly and then titrate the sample with a standard AgNO solution, which has a concentration of 0.0282 or 0.0141 N to reach a pink/red endpoint. Calculation: 1 ml of 0.0282 N AgNO = 1 Mg Cl

Atau mg cl/L=   (X x N x 35450)

                        sample volume (ml)

X = volume of AgNO titrant (ml)
N = normality of AgNO

This method is applicable to 0,15, and 10 mg of chloride.

2. Titrimetric lodometry method

The approach to free chlorine in water is based on the oxidation of potassium iodide with free chlorine to free an equivalent amount of iodine. This liberated iodine is then titrated with a sodium thiosulfate solution using starch as an indicator of the color change of the solution from dark blue to colorless. indicator of the color change of the solution from dark blue to colorless.

Theory: Cl₂ + 2KI  ->  2KCI+l₂

KI +1₂                    ->  Kl3

I2+2Na2 S2 03       -> 2Nal + Na2S4O6

I2 + Starch             -> complex dark blue


This process is referred to as iodometric titration because it uses 1 indirectly for titration. To about 500 ml of sample, add about 5 ml of acetic acid and 1 g of Kl. Put on the stopper, shake vigorously, and leave for some time. Thus, all will be liberated. Next, the L is titrated with a solution of Na.50, a standard with a concentration of 0.025 N, using starch as an indicator. The end point is the color change from dark blue to colorless.

1 ml 0,025 N Na2S2O3 = 0,4 mg Cl2

Calculation: mg cl/L  = (X x N x 35450)

                                   sample volume (ml)

with :

V= Volume Na2S2O3

N= Normality Na2S2O3

This method generally uses a solution with a concentration containing free chlorine of 40 ppm or more.

 3. Alkalinity

The alkalinity of water is a measure of the acid-neutralizing ability of the water. Alkalinity in wastewater arises due to the presence of titrable bases such as hydroxides, carbonates, and bicarbonates. bases such as hydroxides, carbonates, and bicarbonates.

[OH]+H   -> H2O

[CO2]+H -> [HCO2]

[HCO3]+H -> H2O+CO2

Alkalinity is measured by titrating the sample with a standar

Acid such as N/50 H2SO4 The results are expressed as CaCO3. The value of alkalinity depends on the pH and the end point marked in the titration.

pH value

Indikatoir used

End Point



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