Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Environmental Chemistry → Water Chemistry ↓


pH and water hardness


Introduction to pH

In environmental chemistry, the concept of pH is fundamental. pH is a measure of how acidic or alkaline water is and it affects chemical reactions, biological processes, and environmental stability. The pH scale ranges from 0 to 14, where pH 7 is neutral, a pH less than 7 indicates acidity, and a pH greater than 7 indicates alkalinity.

pH = -log[H⁺]

Here, [H⁺] represents the concentration of hydrogen ions in moles per liter. For example, if the hydrogen ion concentration is 1 × 10⁻⁷ moles per liter, the pH is 7, indicating a neutral solution.

0 7 14

Importance of pH in water chemistry

The pH of water significantly affects solubility and biological availability. Many biological systems, like human blood, maintain a strictly regulated pH. Similarly, aquatic ecosystems are sensitive to pH changes. Fish and aquatic life generally thrive within certain pH levels, and deviations can lead to harmful effects.

For example, at low pH levels, metals such as aluminum become more soluble, which can be toxic to aquatic life. Acidic water, often caused by acid rain, can harm plants and animals, while alkaline water can disrupt biological membranes and affect enzyme activities.

Understanding water hardness

Water hardness is determined by the concentration of polyvalent cations, mainly calcium (Ca²⁺) and magnesium (Mg²⁺). Hard water forms deposits and scaling in pipes, boilers and other systems. The hardness scale also varies, with soft water typically containing less than 60 mg/L of calcium carbonate, moderately hard containing 60–120 mg/L, hard water containing 120–180 mg/L, and very hard water containing more than 180 mg/L.

Total hardness = [Ca²⁺] + [Mg²⁺]
Tender Moderately difficult Difficult Very difficult

The role of water hardness

Water hardness is important for both the environment and human health. While hard water is not directly harmful to health, it can cause a number of practical problems. The presence of calcium and magnesium affects the performance of soaps and detergents, increasing consumption. In industrial operations, such as boilers and cooling towers, hard water leads to scaling that can reduce efficiency and increase maintenance costs.

A positive aspect of water hardness is that it contributes calcium and magnesium to the diet, which are beneficial to human health, aiding in bone development and enzymatic function.

Interrelationship between pH and water hardness

There is an interrelationship between pH levels and water hardness. Although they may be independent in some ways, water chemistry often ties these parameters together. For example, at different pH levels, the solubility of carbonates and bicarbonates, which contribute to water hardness, can change.

In alkaline water with a high pH, bicarbonate and carbonate ions may precipitate as calcium carbonate, affecting the hardness level. In contrast, carbon dioxide dissolves more easily in acidic water, increasing hardness.

Measuring pH and water hardness

pH is typically measured using a glass electrode pH meter, with the pH probe immersed in a water sample to obtain an accurate reading. For field measurements, portable pH meters are prevalent, while more accurate instruments are used in laboratories.

Water hardness is usually measured using titration methods such as the EDTA titration method. In this method, a sample is titrated with a chelating agent that forms complexes with metal ions, and the end point is determined with indicators.

CaCO₃ + EDTA → Ca-EDTA + CO₃²⁻

Practical implications and management

Understanding pH and hardness is important for water treatment processes. For example, ion exchange or lime softening processes can be used to soften hard water. These methods remove calcium and magnesium by replacing them with sodium ions or by precipitating them.

Similarly, controlling pH in the water supply ensures safety and efficiency. For drinking water, treatment facilities often adjust pH to prevent corrosion in pipes and limit the solubility of potentially harmful substances.

Conclusion

The study of pH and water hardness plays a vital role in environmental chemistry, which affects biological systems and industrial processes. A clear understanding of their interactions and impacts enables the development of effective water management practices, ensures the sustainability of aquatic ecosystems and promotes public health.


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pH and water hardness

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