Chemistry of water -Part 16-

Analysis of natural waters:

1- Acidity measurement:

When some of the dissolved CO2 interacts with the molecules of water, carbonic acid (H2CO3) is produced. Water becomes acidic, reducing the pH, due to the hydrogen ions found in carbonic acid.
Sodium hydroxide is used to measure the total acidity, in addition to the use of the phenolphthalein indicator (0.5% phenolphthalein in a solution of 50 ethyl alcohol and distilled water). Sodium hydroxide solution is used for calibration, until the pink color appears, the total acidity is equal to 0.2 X n1, if the volume of the sodium hydroxide solution is equal to n1.

Sample of solid phenolphthalein

Sodium carbonate alkalimetry is used to measure the free mineral acidity in the presence of methyl orange. Strong acids like HCl, HNO3, and H2SO4 may have contaminated the water where the case may occur.

2- Hydrotimetric title:

When the waters have high concentrations of calcium and magnesium salts, they are considered to be hard. It is possible to identify five distinct hydrotimetric titles:
We have the following connection: TH= calcium TH+ magnesian TH.

• 1- All of the calcium and magnesium ions that are present in the water are represented by the total hydrotimetric title (TH).
• 2- The total amount of magnesium salts is represented by magnesium TH.
• 3- The calcium TH matches the overall calcium salt content.
• 4- The permanent TH, it is also known as non-carbonate hardness, it is the one that is left over after boiling the water (The hardness of the water is somewhat reduced after boiling).
• 5- The temporary TH (carbonate hardness). It is the one that vanishes following the same boiling and corresponds to the carbonates and bicarbonates of calcium and magnesium.

References:

• [General and inorganic chemistry book- M. Shkhashirou- H. Birqdad- Y. Qodsi- University publications. Algeria]

• [AQUAPROX- Livre: Traitement des eaux de refroidissement. Imprimé en France par EMD S.A.S- 53110 Lassay-les-Chateaux. N° d'imprimeur: 15566- Dépot légal: juin 2006. N° 842- Cyclus print 90°]

• [GÉOCHIMIE DES EAUX CONTINENTALES- Nathalie Gassama. ISBN 9782340-047402 ©Ellipses Édition Marketing S.A., 2021. 8/10 rue la Quintinie 75015 Paris]

• [Introduction to Water Chemistry (Pollution- Treatment- Analysis). Dr. Nasser Al-Hayek. Publication of the Higher Institute for Applied Sciences and Technology (HIAST). Syrian Arab Republic, 2017.]

• "Chapter A2. Selection of Equipment for Water Sampling" (PDF). National Field Manual for the Collection of Water-Quality Data (Report). Techniques of Water-Resources Investigations, Book 9. Reston, VA: U.S. Geological Survey. March 2003.

• Folco Laverdière, Anja Holstein, Laurent Thiebaut, Robert Mallee, Guillaume Gravejat, Benjamin Des clozeaux: Les principales methodes d’analyse,1999, p5.