Water Chemistry: pH and Alkalinity
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Questions and Answers

What is the primary function of a pH meter in determining pH?

  • To measure the temperature of the solution
  • To measure hydrogen ion activity in aqueous solution (correct)
  • To titrate the solution for dissolved solids
  • To calculate the total alkalinity of water

    • How does pH change relate to hydrogen ion concentration?

  • Concentration doubles with each pH unit increase
  • Concentration is constant regardless of pH
  • Concentration decreases by a factor of 5 for each pH unit increase
  • Concentration increases by a factor of 10 for each pH unit decrease (correct)

    • What does the term alkalinity refer to in water chemistry?

  • The pH level of the water
  • The amount of dissolved solids present
  • The temperature of the water sample
  • The capacity of water to accept H+ ions (correct)

    • What is the typical endpoint pH for determining phenolphthalein alkalinity?

    <p>pH 8.3</p> Signup and view all the answers

    What is the purpose of preserving water samples for alkalinity determination?

    <p>To keep the samples cool and prevent changes in chemical composition</p> Signup and view all the answers

    Which of the following describes alkalinity as compared to pH?

    <p>Alkalinity is a capacity factor, while pH is an intensity factor</p> Signup and view all the answers

    Which chemical reaction is commonly used to calculate water alkalinity?

    <p>CaCO3 + 2H+ → Ca2+ + CO2 + H2O</p> Signup and view all the answers

    During total alkalinity determination, which pH endpoint is used?

    <p>pH 4.3</p> Signup and view all the answers

    Which of the following compounds is classified as a carcinogenic agent?

    <p>Benzene</p> Signup and view all the answers

    What is a characteristic feature of dissolved organic carbon (DOC)?

    <p>It passes through a 0.45 micron pore-diameter filter.</p> Signup and view all the answers

    Which factor does NOT influence dissolved organic carbon concentrations in groundwater?

    <p>Water pH level</p> Signup and view all the answers

    Which of the following is NOT categorized as a man-made organic compound?

    <p>Proteins</p> Signup and view all the answers

    What is the common measure for the concentration of organic compounds in aqueous solutions?

    <p>Dissolved organic carbon (DOC)</p> Signup and view all the answers

    What is a potential health concern associated with synthetic organic compounds in natural water?

    <p>Their health effects at low concentrations are unclear.</p> Signup and view all the answers

    Which of the following is a building block of proteins?

    <p>Amino acids</p> Signup and view all the answers

    Which of the following is considered a natural organic matter found in terrestrial water?

    <p>Carbohydrates</p> Signup and view all the answers

    Which of the following factors does NOT affect the toxicity of pesticides in aquatic systems?

    <p>Temperature of the water</p> Signup and view all the answers

    What does a lower LD50 value indicate about a pesticide?

    <p>The pesticide poses greater ecological risks</p> Signup and view all the answers

    What does persistence in pesticides typically refer to?

    <p>The time required for concentration to decrease by 50%</p> Signup and view all the answers

    Which processes contribute to the degradation of pesticides?

    <p>Biodegradation and metabolism</p> Signup and view all the answers

    What contributes to the acidity in natural water?

    <p>Weak acids, particularly CO2</p> Signup and view all the answers

    Which of the following statements about degradates is true?

    <p>Degradates can have greater, equal, or lesser toxicity</p> Signup and view all the answers

    How is risk from pesticide exposure generally calculated?

    <p>Risk = Exposure × Toxicity</p> Signup and view all the answers

    Which method is NOT used for determining total acidity?

    <p>Potentiometric titration to pH 7</p> Signup and view all the answers

    Which statement about water hardness is correct?

    <p>Hardness is correlated with Total Dissolved Solids (TDS).</p> Signup and view all the answers

    What does risk-based assessment for drinking water and food involve?

    <p>Analyzing the concentration effects on human health</p> Signup and view all the answers

    What is the classification for water hardness at 150 mg/L CaCO3?

    <p>Hard</p> Signup and view all the answers

    Which of the following statements reflects the nature of modern pesticides?

    <p>They typically have short half-lives relevant to pest control periods.</p> Signup and view all the answers

    Which of the following is NOT a source of organic compounds in water?

    <p>Geological processes</p> Signup and view all the answers

    What is one effect of organic compounds in water?

    <p>Causing unpleasant tastes and odours</p> Signup and view all the answers

    How is hardness determined from calcium and magnesium tests?

    <p>By summing the individual concentrations in mg/L</p> Signup and view all the answers

    What is preserved by keeping a water sample cool?

    <p>Determination of all kinds of acidity</p> Signup and view all the answers

    What is the detection limit for total amines using gas chromatography?

    <p>0.1 µg</p> Signup and view all the answers

    Which of the following is NOT a factor associated with the impact of pesticides on water quality?

    <p>Temperature of water bodies</p> Signup and view all the answers

    What method is used for the photometric determination of total amines?

    <p>Bromocresol purple</p> Signup and view all the answers

    Which class of pesticides is specifically used to kill snails and slugs?

    <p>Molluscicides</p> Signup and view all the answers

    What happens to pesticides that are not taken up by plants or broken down by other means?

    <p>They reach groundwater sources.</p> Signup and view all the answers

    What is added to samples for preservation of total amines right after sampling?

    <p>Hydrochloric acid (HCl)</p> Signup and view all the answers

    Which component is NOT part of the classification of pesticides?

    <p>Antifungals</p> Signup and view all the answers

    Which of the following is a common additive found in pesticide formulations?

    <p>Wetting agents</p> Signup and view all the answers

    ¿Qué características definen al agua mineral en función de su concentración de CO2?

    <p>El agua mineral se clasifica en baja carbonatación (0.5 a 1.4 g/l), carbonatada (1.4 a 2.5 g/l) y alta carbonatación (&gt; 2.5 g/l).</p> Signup and view all the answers

    ¿Cuál es la diferencia clave entre agua termal y agua fría según su temperatura?

    <p>El agua termal tiene una temperatura superior a 35 °C, mientras que el agua fría tiene una temperatura igual o inferior a 20 °C.</p> Signup and view all the answers

    Define brevemente qué es el agua connata y sus características principales.

    <p>El agua connata es agua atrapada en formaciones rocosas, altamente mineralizada y puede ser más densa y salina que el agua del mar.</p> Signup and view all the answers

    ¿Qué hace que el agua artesiana sea especial en su origen y características?

    <p>El agua artesiana fluye libremente desde un acuífero confinado y tiene un nivel de agua por encima de la parte superior del acuífero.</p> Signup and view all the answers

    ¿Qué define el agua geotérmica y cómo se diferencia de otras aguas?

    <p>El agua geotérmica tiene una temperatura significativamente más alta que la temperatura promedio anual del aire local.</p> Signup and view all the answers

    ¿Cuál es el rango de concentración de Nitrito (NO2-) en aguas superficiales según el contenido químico presentado?

    <p>0 – 0.5 mg/l</p> Signup and view all the answers

    ¿Qué microelemento tiene el rango de concentración más bajo en el contenido químico de aguas superficiales según los datos proporcionados?

    <p>Cadmio (Cd) ≤ 0.0001 mg/l</p> Signup and view all the answers

    Define el contenido de ácidos orgánicos en las aguas superficiales y su rango de concentración según los datos.

    <p>El contenido de ácidos orgánicos es de 0.5 – 15 mg/l.</p> Signup and view all the answers

    ¿Cuál es la concentración máxima permisible de fósforo inorgánico en aguas superficiales según la información química presentada?

    <p>0.01 – 0.5 mg/l</p> Signup and view all the answers

    ¿Qué cantidad de Zinc (Zn) se espera encontrar en aguas superficiales, de acuerdo con los datos químicos disponibles?

    <p>0.003 – 0.10 mg/l</p> Signup and view all the answers

    ¿Cuál es la relación entre la conductividad eléctrica y los sólidos disueltos totales (TDS) en agua?

    <p>La conductividad eléctrica es una medida de la capacidad del agua para transmitir corriente eléctrica, que está directamente relacionada con la concentración de TDS.</p> Signup and view all the answers

    ¿Qué electrodos se utilizan para medir el potencial redox en soluciones acuosas?

    <p>Se utilizan electrodos de platino y cloruro de plata.</p> Signup and view all the answers

    ¿Cómo se determinan los sólidos suspendidos de forma volumétrica?

    <p>Los sólidos suspendidos se determinan utilizando un cono de sedimentación.</p> Signup and view all the answers

    ¿Qué implicación tiene un alto potencial redox en aguas naturales?

    <p>Un alto potencial redox indica una mayor disponibilidad de electrones, lo cual puede afectar la solubilidad de metales pesados en el agua.</p> Signup and view all the answers

    ¿Qué métodos se utilizan para eliminar metales pesados de aguas residuales?

    <p>Se utilizan coagulación, filtración y adsorción para la eliminación de metales pesados.</p> Signup and view all the answers

    ¿Qué se entiende por turbidez en el contexto de la calidad del agua?

    <p>La turbidez se refiere a los sólidos finos que permanecen en el agua después de la sedimentación de sólidos más grandes.</p> Signup and view all the answers

    ¿En qué condiciones se debe medir el potencial redox para obtener resultados precisos?

    <p>El potencial redox debe ser medido en el lugar de muestreo para reflejar las condiciones reales del agua.</p> Signup and view all the answers

    ¿Qué papel juegan los adsorbentes en el tratamiento de aguas con materiales coloidales?

    <p>Los adsorbentes se utilizan para remover materiales coloidales que superan los límites aceptables de concentración en el agua.</p> Signup and view all the answers

    ¿Qué información proporcionan los índices individuales en la hidroquímica del agua?

    <p>Los índices individuales permiten determinar el contenido químico del agua, como pH, alcalinidad y dureza.</p> Signup and view all the answers

    ¿Qué significa que un sólido se clasifique como 'sólido sedimentable'?

    <p>Un sólido sedimentable es pesado y grande, lo que le permite asentarse fácilmente en el fondo de un recipiente.</p> Signup and view all the answers

    Study Notes

    pH and pOH

    • pH is a measurement of hydrogen ion activity in water.
    • pH can be measured with a pH meter or through titration if the concentration of hydrogen ions is high enough.
    • pH is a logarithmic function and a decrease of one unit of pH represents a tenfold increase in hydrogen ion concentration.
    • pH determination is performed immediately after sampling without preservation.

    Water Alkalinity

    • Alkalinity is the capacity of water to accept hydrogen ions (protons).
    • Alkalinity is important in water treatment and the chemistry and biology of natural waters.
    • High alkalinity often corresponds to high pH and high levels of dissolved solids.
    • It's crucial to distinguish between basicity (high pH) and alkalinity (capacity to accept protons).
    • Alkalinity is typically expressed as mg/L of CaCO3.

    Determination of Alkalinity

    • Phenolphthalein alkalinity is determined by titration with acid to a pH of 8.3, where HCO3- is the predominant carbonate species.
    • Total alkalinity is determined by titration with acid to a pH of 4.3, where both bicarbonate and carbonate have been converted to CO2.
    • Hydroxide alkalinity is measured by precipitating carbonate with BaCl2 and then titrating with standard acid to the phenolphthalein endpoint.
    • To preserve samples for all alkalinity determinations, keep them cool.

    Water Acidity

    • Water acidity is its capacity to neutralize OH- ions.
    • Acidity often results from the presence of weak acids like CO2, proteins, fatty acids, and acidic metal ions like Fe3+.

    Determination of Acidity

    • Total acidity is determined by titration with a standard base to the phenolphthalein endpoint.
    • Free mineral acidity is measured by titration with standard base to the methyl orange endpoint or potentiometrically to a pH of 4.5.
    • To preserve samples for all acidity determinations, keep them cool.

    Distribution of Species Diagram for the CO2, HCO3-, CO32- System

    • This diagram illustrates the relative concentrations of these species in different pH ranges.

    Hardness of Water

    • Hardness is related to total dissolved solids (TDS) and represents the concentration of Ca2+ and Mg2+ ions.
    • Hardness is expressed as mg/L of CaCO3.
    • Hardness can be determined by calculating from calcium and magnesium tests or via titration with ethylenediaminetetracetic acid (EDTA).

    Relation Between Hardness Concentration and Classification

    • Soft Water: 0 – 60 mg/L CaCO3
    • Moderately Hard Water: 61 – 120 mg/L CaCO3
    • Hard Water: 121 – 180 mg/L CaCO3
    • Very Hard Water: >180 mg/L CaCO3

    Organic Compounds in Water

    • Organic compounds in water can be derived from living organisms, domestic use, agricultural applications, and industrial sources.
    • Organic compounds can cause taste and odor issues in drinking water and some can be carcinogenic or cancer-suspect agents.

    Natural Organic Matter

    • Naturally occurring organic compounds in water include:
      • Carbohydrates (sugars, cellulose)
      • Lipids (neutral fats)
      • Proteins (amino acids)
      • Enzymes
      • Complexes of proteins with other organic compounds

    Man-Made Organics

    • These synthetic organic compounds include aliphatic and aromatic compounds.
    • Many are found in water at low concentrations and their health effects are often unknown.
    • Examples include chlorinated solvents, pesticides, petroleum components, and synthetic chemicals.

    Dissolved Organic Carbon (DOC)

    • DOC is a measure of organic compounds in water.
    • It is the fraction of total organic carbon (TOC) that passes through a 0.45 micron filter.
    • DOC is determined by:
      • Removing inorganic carbon species
      • Oxidizing organic material to carbon dioxide (micro dichromate oxidation)
      • Quantifying the carbon dioxide produced
    • Typical DOC concentrations in groundwater range from a few micrograms to several tens of mg per liter.
    • DOC concentration depends on:
      • Climate
      • Soil and vegetation cover
      • Land use

    Amines

    • Total amines are measured photometrically with Bromocresol purple after separation by diffusion.
    • This method has a detection limit of 1 µg N/l.
    • Gas chromatography can also measure amines with a detection limit of 0.1 µg.
    • Samples should be preserved by adding HCl to adjust the pH to 4-5.
    • In the lab, filter samples through a 0.45 micron filter and add HCl to adjust the pH to 1-2.

    Pesticides

    • Pesticides are chemicals used to kill or control pests.
    • They include herbicides, insecticides, fungicides, nematocides, rodenticides, molluscicides, avicides, piscicides, bactericides, slimicides, and algicides.

    The Pesticide Cycle

    • Pesticides can be applied directly to soil, water, or crops.
    • Some pesticides are absorbed by plants, while others remain in the environment.
    • Pesticides can be transported by wind, water, or wildlife.
    • They can accumulate in soil, water, and organisms over time.

    The Impact of Pesticides on Water Quality

    • The impact of pesticides on water quality depends on the following factors:
      • Active ingredient of the pesticide formulation
      • Contaminants in the active ingredient
      • Additives mixed with the active ingredient
      • Degradates formed during chemical, microbial, or photochemical degradation

    How Do Pesticides Get Into Water Supplies?

    • Pesticides that are not absorbed by plants, adsorbed by soil, or broken down can reach groundwater sources.
    • Factors influencing this include:
      • Type of soil
      • Depth to groundwater
      • Chemical properties of the pesticide
      • Amount and timing of precipitation or irrigation

    Factors Affecting Pesticide Toxicity in Aquatic Systems

    • The environmental impact of pesticides is determined by:
      • Toxicity
      • Persistence
      • Degradates
      • Environmental fate

    Toxicity

    • Toxicity is expressed as the LD50 (Lethal Dose) which is the concentration that kills 50% of test organisms.
    • Lower LD50 values indicate higher toxicity.
    • Drinking water and food guidelines are based on risk assessment, which considers exposure and toxicity.
    • Toxic responses can be acute (death) or chronic (observable effects like cancer, reproductive failure, growth inhibition, or teratogenic effects).

    Persistence

    • Persistence is measured as half-life, the time it takes for the chemical to degrade by 50%.
    • Modern pesticides tend to have short half-lives to address short-term pest control needs.

    Degradates

    • Pesticide degradation can lead to the formation of degradates, which may be more, equally, or less toxic than the parent compound.
    • For example, DDT degrades to DDD and DDE, which can contaminate commercial DDT preparations.

    Chemical Content of Surface Waters

    • Biogenic Elements:
      • Total iron: Between 0.01 and 2 mg/l
      • Total silicon: Between 1 and 10 mg/l
      • Organic phosphorus: Between 0.01 and 0.2 mg/l
      • Inorganic phosphorus: Between 0.01 and 0.5 mg/l
      • Organic nitrogen: Between 0.2 and 2 mg/l
      • Nitrate: Between 0 and 2 mg/l
      • Nitrite: Between 0 and 0.5 mg/l
      • Ammonium and ammonia: Between 0.02 and 1.5 mg/l
    • Microelements - Industrial Pollutants:
      • Cadmium: ≤ 0.0001 mg/l
      • Lead: Between 0.0001 and 0.005 mg/l
      • Chromium: Between 0.0001 and 0.005 mg/l
      • Nickel: Between 0.0005 and 0.01 mg/l
    • Microelements – Biometals:
      • Cobalt: Between 0.0001 and 0.005 mg/l
      • Molybdenum: Between 0.0005 and 0.01 mg/l
      • Copper: Between 0.002 and 0.05 mg/l
      • Zinc: Between 0.003 and 0.10 mg/l
      • Manganese: Between 0.002 and 1 mg/l
    • Organic Compounds:
      • Carbonyl compounds: Between 0.02 and 2 mg/l
      • Esters: Between 0.05 and 8 mg/l
      • Organic acids: Between 0.5 and 15 mg/l
      • Carbohydrates: Between 0.01 and 2 mg/l
      • Saccharides: Between 0.05 and 2 mg/l
      • Amines: Between 0.03 and 3 mg/l
      • Amino acids: Between 0.004 and 5 mg/l
      • Proteins: Between 0.02 and 5 mg/l
      • Fulvic acids: Between 0.5 and 10 mg/l
      • Humic acids: Between 0.02 and 2 mg/l

    Maximum Permissible Concentrations for Surface Water

    • This information is based on SK 296/2005

    Mineral Water Classifications

    • Based on Carbon Dioxide Concentration:
      • Low-carbon: Between 0.5 and 1.4 g/l
      • Carbonated: Between 1.4 and 2.5 g/l
      • High-carbon: > 2.5 g/l
    • Based on Hydrogen Sulfide Concentration:
      • Low sulfide: Between 10 and 50 mg/l
      • Moderately sulfide: Between 50 and 100 mg/l
      • High sulfide: Between 100 and 250 mg/l
      • Very high sulfide: > 250 mg/l
    • Based on pH Level:
      • High acid: Between 3 and 3.5
      • Acid: Between 3.5 and 5.5
      • Low acid: Between 5.5 and 6.8
      • Neutral: Between 6.8 and 7.2
      • Low alkaline: Between 7.2 and 8.5
      • Alkaline: > 8.5
    • Based on Temperature:
      • Cold: ≤ 20°C
      • Warm: Between 20 and 35°C
      • Hot (thermal): Between 35 and 42°C
      • Very hot: > 42°C

    Artesian Water

    • Artesian water is groundwater that flows freely upwards out of an artesian bore or well.
    • It comes from a confined aquifer, where the water level in the well is at a higher elevation than the top of the aquifer.
    • Artesian water may also be relatively highly mineralized due to long travel times and may contain gases and dissolved iron, which can precipitate on the surface.

    Connate Water

    • Connate water is water trapped in the pores of rock at the time of formation.
    • Due to long contact with rock material, connate water can change chemical composition and become highly mineralized.
    • It can be more dense and saline than seawater, with salinities ranging from 20 to over 300 grams per liter.

    Geothermal Water

    • Geothermal water has a temperature significantly higher than the local average annual air temperature.
    • Suspended solids are determined through filtration, drying, and weighing.
    • Settleable solids, which are large and heavy, can be measured volumetrically in a settling cone or weighed.
    • Fine suspended solids that remain in the supernatant water are called turbidity.
    • Adsorbents are used to remove colloidal materials when they exceed acceptable concentration limits.
    • Heavy metals are often present in colloidal form and are removed through coagulation, filtration, adsorption, or a combination of these methods.

    Redox Potential (Eh)

    • Eh is a measure of the number of electrons in solution in an aqueous solution.
    • It depends on dissolved gases in natural waters and should be determined at the sampling location.
    • Measurement is done using platinum and silver chloride electrodes.
    • Calculated using the Nernst equation.

    Electrical Conductivity

    • The concentration of total dissolved solids (TDS) is related to electrical conductivity (EC), measured in mhos/cm.
    • Conductivity reflects the water's ability to transmit electrical current.
    • TDS and conductivity affect the water sample and the solubility of slightly soluble compounds and gases in water (e.g. CaCO3 and O2).

    Hydrochemistry - Individual Indexes for Determining Chemical Content of Water

    • Part I:
      • pH and pOH
      • Dissolved oxygen
      • Hydrogen sulfide and sulfides
      • Acidity and alkalinity
      • Components of the carbonate system
      • Chlorides and sulfates
      • Hardness of water
      • Potassium and sodium
      • Calcium and magnesium

    Water Acidity

    • The capacity of water to neutralize OH-.
    • Caused by the presence of:
      • Weak acids, primarily CO2
      • Sometimes proteins and fatty acids
      • Acidic metal ions, primarily Fe3+

    Determination of Acidity

    • Total acidity: Titration with a standard base to the phenolphthalein endpoint.
    • Free mineral acidity: Titration with a standard base to the methyl orange endpoint or potentiometrically to pH 4.5.
    • To preserve samples for acidity determination, keep them cool.

    Distribution of Species Diagram for the CO2, HCO3-, CO32- System

    • This diagram is used to visualize the relative concentrations of the species as a function of pH for a given system.

    Hardness of Water

    • Represents the total concentration of Ca2+ and Mg2+ ions.
    • Expressed in equivalent CaCO3.
    • Determined through:
      • Calculation from separate calcium and magnesium tests
      • Titration with ethylenediaminetetracetic acid (EDTA)

    Relation Between Hardness Concentration and Classification of Natural Water

    • Soft: 0-60 mg/L CaCO3
    • Moderately hard: 61-120 mg/L CaCO3
    • Hard: 121-180 mg/L CaCO3
    • Very hard: >180 mg/L CaCO3

    Organic Compounds in Water

    • Derived from:
      • Living organisms
      • Domestic use
      • Agricultural applications
      • Industrial sources:
        • Chemical industries
        • Petrochemical industries
    • Affect water quality by:
      • Causing disagreeable tastes and odors in drinking water.

    Factors Affecting Pesticide Toxicity in Aquatic Systems

    • Ecological impacts of pesticides are determined by:
      • Toxicity
      • Persistence
      • Degradates
      • Environmental fate

    Toxicity

    • Expressed as LD50 (Lethal Dose): the concentration of the pesticide that kills 50% of test organisms within a specified time period.
    • Lower LD50 indicates greater toxicity.
    • Drinking water and food guidelines are determined using risk-based assessments (Risk = Exposure × Toxicity).
    • Effects can be acute (death) or chronic (observable effects like cancers, reproductive failure, growth inhibition, etc.).

    Persistence

    • Measured as half-life (time required for the ambient concentration to decrease by 50%).
    • Persistence is determined by biotic (biodegradation and metabolism) and abiotic (hydrolysis, photolysis, oxidation) processes.
    • Modern pesticides tend to have short half-lives to match the pest control period.

    Degradates

    • Degradational processes can lead to the formation of degradates with greater, equal, or lesser toxicity than the parent compound.
    • For example, DDT degrades to DDD and DDE. DDE (dichlorodiphenyldichloroethylene) is a similar, non-commercial chemical to DDT that is considered a contaminant. DDE has no commercial use.

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    Description

    This quiz covers key concepts related to pH and alkalinity in water chemistry. It focuses on measuring hydrogen ion activity, the importance of alkalinity in water treatment, and methods for determining alkalinity through titration. Test your understanding of these fundamental concepts essential for water quality assessment.

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