Acid-Base Reactions: Volumetry and Electrochemistry

• Acid-base reactions encompass volumetry and electrochemical methods.

Introduction to Practical Context

• Enlace formation between atoms arises from attractions between positive and negative charges.
• Chemical reactions involve reactants forming products through atom and electron redistribution.
• Chemical reactions are classified into: precipitation of ionic salts and solutions, acid-base reactions, and oxidation-reduction reactions.
• Electrocemistry is fundamental branch of chemistry focused on redox reactions.

Volumetry

• Most substances break down into ions, creating acids and bases that, when combined, trigger neutralization.
• Acid + Base -> Salt + Water reactions
• Acid-base volumetry determines the concentration of an acid or base analyte, given a known concentration of the other, in a volumetric method.
• Titration is another name for this technique.
• Volumetry types are neutralization, precipitation, redox, and complex formation.
• Neutralization volumetry includes:
  • Acidimetry: Determining acid concentration using a known base concentration like sodium hydroxide (NaOH) or potassium hydroxide (KOH).
  • Alkalimetry: Determining base concentration using a known acid concentration like hydrochloric acid (HCl), sulfuric acid (H2SO4), or nitric acid (HNO3).

Acid-Base Titration

• Technique known as titration leverages the neutralization reaction between acids and bases.
• A standard solution with a known concentration is used to find the concentration of another substance (problem sample).
• Using equivalent-gram amounts is essential.
• A wide range of acid-base titration applications are used, including:
  • Measuring mixtures of carbonates and bicarbonates.
  • Determining hydroxides with or without carbonates.
  • Industrial waste control for water contamination.
  • Water analysis.
  • Analysis of industrial fertilizers and detergents.
  • Hygiene product creation, such as shampoos and gels.
• Petrochemical sector uses them to check the aging of oil, pharmaceutical to create medicines, and determine nitrogen in organic compounds

Performing an Acid-Base Titration

• Using a known concentration of a substance, called the standard solution, to determine the concentration of another substance (problem sample).
• Reaction of samples should be an equivalent-gram to equivalent-gram to ensure equal moles.
• Solution is neutral at pH 7 after neutralization, called the equivalence point.
• This can change based on solution strengths like a strong acid reacting with a strong base, resulting in a pH neutral.
• A strong acid reacting with a weak base will result in an acidic solution (pH < 7) and a weak acid with a strong base yields a basic solution (pH > 7).
• Acid-base titrations with a precise volume of HCl in an Erlenmeyer flask with a known volume and concentration of NaOH (strong base) in a burette.
• Add NaOH from the burette dropwise into the HCl till the equivalence point with the aid of an indicator like phenolphthalein.

Electrochemical-methods

• Electrochemical methods determine the concentration of a substance using electrochemistry, including neutralization titrations and buffer solutions.
• Conductimetry and potentiometry are widely used in laboratories.
• Needed materials include: a reference electrode, an indicator electrode, and a potential measuring device.
• Redox reactions are involved in the study of chemical reactions and electricity in electrochemistry.
• Agents/Substances that are reducing release electrons, causing oxidation and substances that are oxidizing accept electrons, which means that they are reduced.

Electrode Potential

• Redox reactions induce a current resulting from the potential difference between reduction and oxidation.
• Electrode potential/Standard potential (E°) indicates the potential difference at 1 atm pressure and 25°C, measured in Volts (V).
• Redox reactions can be split into two:
  • Oxidation semireaction: loss of electrons (e-) as an anode.
  • Reduction semireaction: gain of electrons (e-) as a cathode.
• The formula for potential differences indicates the difference between cathodes and anodes.

Electrode-Types

• To determine electrode potentials, it is necessary to have a reference electrode known as the standard hydrogen electrode (SHE).
• This electrode maintains standard conditions, being immersed in a 1M hydrochloric acid solution at room temperature (25°C).
• Its E° value is zero.
• Reduction potential for an electrode outside of standard conditions is calculated using the Nernst equation.
• Reference electrode types are hydrogen electrodes, calomel electrodes (mercury with mercury (I) chloride and potassium chloride solution), and silver/silver chloride electrodes (silver with saturated potassium chloride and silver chloride solution, which can be used at T > 60°C).
• Indicator electrodes such as Metallic electrodes (gold, platinum, palladium, etc.) for redox reactions, and ion selective electrodes (membrane).

Classification of Electrochemical Methods

• Electrochemical approaches assess a substance's properties for electrochemical concentration determination.
• Redox reactions involve electron exchange because of electric charges.
• As charges accumulate between two electrodes, a spontaneous current is created, requiring electric current.
• Electrochemical cells are galvanic and electrolytic.
  • Galvanic cell: Voltaic cell obtains electrical energy spontaneously with redox reactions.
  • Electrolytic cell: Requires energy to catalyze redox reactions, i.e. electrolisis.

Conductimetry

• Conductimetry measures the conductivity of electrolytes (that contain free ions).
• This technique uses positive ions going to the cathode and negative ions going to the anode, creating a flow called conductance.
• Concentration of a solution's electrolyte can be measured through conductimetric titration.
• Can be value saturated, turbid, and colored solutions.
• Conductance changes in acid-base reactions are more significant than the process of precipitation.

Potentiometry

• Potentiometry determines electrolyte concentration measuring the potential difference in a cell (E° cell = E° cathode - E° anode).
• Reference electrode, indicator electrode, and potential measuring device are the same tools as before.
• Reactions that occur in a cell can be spontaneous (galvanic), or provoked (electrolytic), the electrolysis reactions are reduction and oxidation.
• In galvanic cells, the positive electrode is the cathode, and the negative is the anode.

Direct Potentiometric Measures

• Direct potentiometric measurements complete chemical analysis of substances that have been measured using an indicator electrode.
• The pH can be measured, however the glass used has limitations.
• Errors can influence how well it measures.

Indirect Potentiometric Measures

• Titrations (potentiometric titrations) provide more precise data than using indicators with pH meters.
• Methods include:
  • Acid-base titrations: A glass electrode and a mercuric reference electrode are needed.
  • Precipitation titrations: Silver nitrate determines halides, sulfides, and phosphates, indicated by silver.
  • Complex formation titration: EDTA forms complexes with metallic ions, except those of lithium (Li), sodium (Na,) and potassium (K).
  • Redox titrations: Galvanic cells (spontaneous redox) or electrolytic cells (redox with electrical energy input).

Practicing Calibrating the Electrode.

• If Andres must measure some solutions, he will nedd to use a pH-meter.
• pH-meters need to be calibrated to ensure accuracy in measuring pH.
• Calibration varies by electrode type and compares to a reference solution.
  • Single calibration tests the buffer using a buffer tampon.
  • Two calibrations evaluate acids (pH = 4) and bases (pH = 9).
  • Three calibrations tests the complete scale (pH 4, pH 7, pH 9) and uses all types.

Applications of Electrochemical Methods.

• María, who will practice an electrochemical evaluation, asks her teacher what it is.
• Redox valuation is the transfer of electrons by an oxidation and reduction.
• To produce oxidation, zinc releases electrons when the solutions are bound by a conductor.
• Use a salt bridge to maintain potential between cells.

Clinical and Anatomopathological Lab Applications.

• Many chemical reactions require a constant pH to prevent undesired changes, so we utilize buffer equations.
• Acid-base volumetry is commonly used.
• Potentiometric techniques allow for analysis of ions, gas and air quality, and more.
  • Ion analysis in industrial processes
  • Quality measurement of contaminated gases and air
  • Electrolyte determination in physiological fluids.
  • Biosensor manufacturing using enzymes
  • pH determination
  • Determination of the final point in acid-base titrations and/or redox.

Unit Summary and Practical Case Resolution

• Different types of chemical reactions exist, such as acid-base valuations (neutralization, precipitation, redox, and complex formation) and electrochemistry which hightlings conductimetry and potentiometry.
• Electrode potentials are differentiated by reduction and oxidation.
• There are diverse electrode types like hydrogen, calomelano, silver, metal, selective ions, glass, and biosensors.
• There are diverse electrochemistry approaches, which mainly look at conductometric and potentiometric techniques used for titrations and pH checks.
• Electrode potential considers the measure of oxidation-reduction, which is explained by G = -nFE°.
• The voltage creates a positive E° ( > 0) for spontaneous reactions.