Chemical Analysis Basics

Introduction to Analytical Chemistry

• Analytical chemistry is a measurement science involving experimentation, observation, and senses.
• It uses powerful ideas and methods applicable to various fields of science & medicine.
• Focuses on theoretical & practical methods for determining the composition of matter, sample composition and all transformations.
• Analytical chemistry evolved into a science with interdisciplinary applications in industry, medicine, and scientific fields.
• An analyst performs an analysis on a sample.
• An analysis/assay is a test/examination to investigate characteristics, identify components, or determine the absence, presence, or quantity of a substance.
• The main goal is to know a sample composition.
• Matter is paramount in chemistry.
• Matter has mass and occupies space.
• Samples are mixtures that contain both the analyte and impurities.
• The analyte is the substance being analyzed and must have a defined chemical formula.
• Other terms for analyte include chemical species, chemical constituent, and substance (or compound) of interest.
• Mass (g) sample = mass (g) analyte + mass (g) impurities.

Applications

• Analysis determines the quality of manufactured products, supports legislation, and backs legal processes like forensic science.
• Analyses are conducted to relate chemical composition to physical properties.
• Analyses determine the quality of manufactured products for routine processes (screening, surveillance, monitoring) and process control.

Qualitative vs Quantitative Analysis

• Qualitative analysis identifies substances (elements or compounds) in a sample.
• Quantitative analysis determines the concentration/amount of an analyte in a sample.

Classifying Quantitative Analytical Methods

• Analytical methods are classified by the nature of the final measurement.
• Measurements include the final mass/volume and some other quantifiable property that is proportional to the amount of analyte in the sample.

Quantitative Analytical Methods

• Classical methods include gravimetric and volumetric/titrimetric methods.
• Gravimetric approaches measures the mass of the analyte or directly related compound (thermogravimetric is for temperature).
• Volumetric approaches measures the volume of a solution that contains sufficient reagent for complete reaction with the analyte.
• Instrumental methods include spectroscopic, chromatographic, and electroanalytical methods.
• Spectroscopic methods measures the interaction between electromagnetic radiation and analytes and includes aborpstion, Infrared, NMR, and X-Ray Spectroscopy.
• Electroanalytical methods involve measuring electrical properties of such voltammetry, amperometry, and coulometry.

Sample Size

• Sample size and analyte composition matters.
• Macro: > 0.1g, > 100mg
• Semimicro: 0.01 to 0.1g, 10 to 100mg
• Micro: 0.0001 to 0.01g, 1 to 10mg
• Ultramicro: < 0.0001g, 0.1mg

Extent of Analysis

• Complete/Ultimate: Measures the amount of all constituents.
• Partial/Proximate: Measures the amount of selected constituents.
• Proximate analysis of a food sample involves determining the total protein, fat, ash, carbohydrates, and moisture, reported as percentages.
• Relative contribution of the analyte:
• Major: >1%
• Minor: 0.01 to 1%
• Trace: <0.01% or 1 parts per billion (ppb) to 100 parts per million (ppm)
• Ultratrace: <1ppb

Choosing an Appropriate Analytical Method

• Ensure a high quality analysis and suitability of the assay for the sample.
• The analytical method depends on available quantity and relative distribution of analyte.
• Elementary entities are unit particles
• Demarcation line divides metals and non-metals
• Molecules are formed from non-metals
• Formula units: Used only for ionic compounds with more than one element.
• 1 mole = molar mass.

Important Chemical Concepts

• Mole & Mass
• The mole is amount containing same elementary entities as atoms in 12 g of carbon-12.
• A mole is a unit to count particles like atoms, molecules, etc.
• 1 mole = molar mass (gram)
• Molar mass = mass (g)/1 mole
• Molar mass = 58.44 g NaCl/mole NaCl.
• 1 mole = 1000 millimole
• 1000 milliomole = Molar mass (gram)
• Conversions:
• Molar mass = mass (g) / 1 mole
• Molar mass = mass (g) / 1000 mmole
• Molar mass = mass (mg) / 1000 mmole

Calculating Substance Amounts

• Mole NaCl = 0.624 g NaCl x (1 mole NaCl / 58.44 g NaCl) = 0.0107 mole NaCl
• Mass (g) NaCl = 0.22 mole NaCl x (58.44 g NaCl / 1 mole NaCl) = 13 g NaCl
• Mmole NaCl = 0.1174 g NaCl x (1000 mmole NaCl / 58.44 g NaCl) = 2.009 mmole NaCl

Solutions & Concentrations including Molarity

• Chemical concentration indicates how much solute is in a given volume or mass of solution/solvent.
• Molarity/Molar Concentration is the moles of solute per liter of solution
• M = Amount (moles) of Solute/ Volume (L) of Solution
• M = Amount (mmoles) of Solute/ Volume (mL) of Solution
• To compute the grams of KOH present:
• M KOH = (x g KOH / 35.0 mL) * (1000 mmole KOH / 56.11 g KOH) = 5.50 M
• x g KOH = (5.50 M)(35.0 mL)(56.11 g KOH) / 1000 mmole KOH = 11 g KOH

Standard Solutions

• A standard solution’s concentration is accurately known and expressed to at least four (4) significant figures.
• This prep is suited for the solutions where the solute is a primary standard soluble (or slightly soluble) solvent.

Preparing a standard solution in 3 steps

• Pour solvent into a beaker and transfer accurately weighed solute portions into the beaker; stir.
• Transfer the dissolved mixture into a volumetric flask quantitively, and dilute to the mark.
• Stopper, invert, & shake to ensure the mixture is homogenous.

Percent Concentration

• Mass %A (w/w) = (Mass Solute A / Mass of Solution) * 100
• Volume %A (v/v) = (Volume of Solute A / Volume of Solution) * 100
• Mass/Volume %A (w/v) = (Mass (g) of Solute A / Volume (mL) of Solution) * 100

Molarity

• Density = Mass/Volume
• Volume = 37.9 g HCl / 37.0 g HCI x 1.19 g/mL = 31.092 mL

Specific Gravity

• Specific gravity is the ratio of a substance's mass to the mass of an equal volume of water.
• Sp gr = (Mass (g) X / Mass (g) H₂O).

Dilution of Solutions

• Dilution prepares less concentrated solution (dilute solution) from more concentrated solution (stock solution).
• "Dilute to" means adding enough water to reach the final volume
• Ex: Dilute to 500 mL. Total = 500 mL
• "Dilute With" means that the solvent is added to stoc solution.
• Ex: Dilute with 500 mL, Total = 500 mL + Stock Solution (25 mL) = 525 mL
• CCONCVCONC = CDILUTEV DILUTE
• N-fold Dilution decreases the stock solution concentration by n-fold, dilution formula is CDILUTE =CCONC/n

Chemical Reactions

• Stoichiometry is the quantitative relationship among reacting chemical species. General strategy:
• Mass A x (a Moles A / MM (g) A) x (b Moles B / a Moles A) x (MM (g) B / b Moles B)= Mass B Reactions Involving Aqueous Solutions: (Volume of B = Mass A (a Moles A / MM (g) A) X (b Moles B / a Moles A) x (1000 mL/b Moles B)

Titration

• Titration uses analytical technique to determine the quantity of a reagent to react completely with the analyte
• Titrimetric methods include quantitative procedures to determine the quantity of a reagent of known concentration.

Reagent

• Reagents can be standard solutions or an electric current of known magnitude.
• Various titrimetric applications depend on the measured property when the reaction is considered to be complete, including the analytical process:
• Volumetric titrimetry: measures the volume of a known concentration that is needed to react completely with the analyte (Requires a precise buret).
• Gravimetric or weight titrimetry: measures the mass of a known concentration that is needed to react completely with the analyte (Requires a sensitive analytical balance).
• Coulometric titrimetry: measures the charge in coulombs required to complete a reaction with the analyte. (Applicable to RedOx Reactions). Important terms: Analyte (test analyte) reacts with the reagent solution is accurately known (must occur in the dissolved state)
• Test analytes react with a reagent whose concentration is accurately known.
• In titrimetry, this must occur in the dissolved state contained by an Erlenmeyer/conical flask.

More Titration Terms

• Titrant: Solution added in precise increments, concentration must be known.
• Equivalence point: Is theoretical state that cannot determined experimentally.
• End Point: Is experimental state when observable/physical change occurs that associates w/ chemical equivalence (signifies reaction completion).
• Indicators - These are added to analyte solution for physical change (the end point) at or near the equivalence point.
• Titration Error: The is the difference in volume/mass between the equivalence point and the end point with the formula, E₁ = VEND PT-VEQUIV PT
• Primary standard is a highly purified compound reference
• It high purity and atmospheric stability
• There must be an absence of hydrate water and modest cost.
• Reasonable soluble in medium

Analyzing titration data

• Significant change in the solution property happens at the equivalence point. The end point should coincide as closely as possible.
• Deliquescent substances forms into aqueous vapours to absorb water. While efflorescent substances does vapor do not absorb water vapor.
• Hygroscopic substances will absorb water vapor, but will not form any aqueous solution.
• Secondary standards will is a chemical composition that serves reference w/ reference material.
• Standard Solution- reagent on titrimetric analysis that is concentration of solution

Ideal Conditions For Titration

The ideal standard solution for a Titrimetric method will:

• stable and have selective reaction w/ the analyte.
• react rapidly and completely w/ balance equation.

For Titration Reactions

The standard solution is often a strong acid that donates protons (H+) or a proton acceptor(negatively charged O(Oxygen), base

• Acidic solutions is hydrochloric

Requirement is measured properly.

• The reaction w must be quantitative w/ analytical equation

Acids & Bases.

• Bases are proton (H+) acceptor, negatively
• Acids will proton (with donate with acidic HS H.
• Acidic compound is a donating proton (H+) will reacted

Normality of Solutions (titration)

• Primary standard is base & Acid will standardized a standard titration. Monoprotic acid: ONE (acid) proton equivalent, DIProtic:Two acid proton (equivalents)

Method to compute molar for acidic.

Explore chemical analysis principles, objectives, and terminology. Understand its role in product quality assurance and legislative support. Learn about titrations, including neutralization reactions.