Study guide
5.1 Analytical Measurements: Apparatus, Units, Concentration, Sampling, and Sample Preparation
PRC Chemist Licensure Examination Exam
Track your progress as you read
Finished sections get a check mark.
1 Chapter 1: Exam Overview, Chemistry Law (RA 10657), and Laboratory Safety
1.1 PRC Chemist Licensure Examination: Format, Schedule, Grading, and Passing Standards 1.2 Republic Act 10657 (Chemistry Profession Act) and Professional Ethics 1.3 Chemical Laboratory Safety, GHS Classification, Hazardous Waste Management, and Quality Assurance
2 Chapter 2: Inorganic Chemistry: Atomic Structure, Periodicity, and Chemical Bonding
2.1 Atoms, Ions, Compounds, Inorganic Nomenclature, and Stoichiometry 2.2 Quantum Numbers, Electronic Configurations, and Periodic Trends 2.3 Chemical Bonding Models: Lewis Structures, VSEPR Theory, and Molecular Polarity 2.4 Molecular Orbital Theory and Magnetochemistry of Diatomic Molecules
3 Chapter 3: Inorganic Chemistry: Coordination Compounds and Transition Metals
3.1 Coordination Chemistry: Nomenclature, Formulas, and Isomerism 3.2 Crystal Field Theory, Ligand Field Theory, d-Orbital Splitting, and Reaction Mechanisms 3.3 Electronic Absorption Spectra, Tanabe-Sugano Diagrams, and Magnetic Properties
4 Chapter 4: Inorganic Chemistry: Main Group, Reactivity, Solid State, Nuclear, and Applied Topics
4.1 Systematic Descriptive Chemistry of Main Group Elements (s- and p-Blocks) 4.2 Reactivity of Inorganic Compounds: Acid-Base Concepts, HSAB, and Redox Diagrams 4.3 Solid-State Chemistry: Crystal Systems, Unit Cells, and Band Theory 4.4 Bioinorganic Chemistry: Metalloproteins, Oxygen Carriers, and Metal Ion Toxicity 4.5 Organometallic Chemistry: 18-Electron Rule, Carbonyl Complexes, and Catalysis 4.6 Nuclear Chemistry: Stability, Decay, Transmutation, and Radioanalytical Methods 4.7 Industrial, Environmental, and Atmospheric Inorganic Chemistry and Advanced Materials
5 Chapter 5: Analytical Chemistry: Measurements, Statistics, Classical Wet Analysis, and Chemical Equilibria
5.1 Analytical Measurements: Apparatus, Units, Concentration, Sampling, and Sample Preparation 5.2 Analytical Data Evaluation: Errors, Uncertainty, Statistics, and Calibration 5.3 Gravimetric Analysis and Precipitation Equilibria ($K_{sp}$) 5.4 Neutralization Titrimetry, Polyprotic Systems, Buffers, and Alpha Fractions 5.5 Complexometric (EDTA), Redox, and Precipitation (Argentometric) Titrimetry
6 Chapter 6: Analytical Chemistry: Electroanalytical Methods and Separations
6.1 Potentiometry, Ion-Selective Electrodes, and Voltammetric Techniques 6.2 Analytical Separations: Solvent Extraction, SPE, Ion Exchange, Precipitation, Masking, and Electrodeposition 6.3 Fundamentals of Chromatography: Theoretical Plates, Resolution, and van Deemter Equation 6.4 Gas Chromatography (GC): Columns, Stationary Phases, Detectors, and Applications 6.5 High-Performance Liquid Chromatography (HPLC): Normal vs. Reversed Phase and Method Development
7 Chapter 7: Analytical Chemistry: Spectroscopic, Mass Spectrometric, and Other Instrumental Methods
7.1 Molecular UV-Vis Spectroscopy and Quantitative Beer-Lambert Law 7.2 Infrared (FTIR) and Raman Spectroscopy: Vibrational Modes and Instrumentation 7.3 Atomic Spectroscopy: Atomic Absorption (AAS) and Inductively Coupled Plasma (ICP-OES/MS) 7.4 Mass Spectrometry: Ionization Sources, Mass Analyzers, and Fragmentation Analysis 7.5 Other Instrumental Methods (XRF, Flame Emission, CE, SFC, Thermal Analysis, Electronics) and Method Selection
8 Chapter 8: Physical Chemistry: Gases, Thermodynamics, and Thermochemistry
8.1 Ideal and Real Gases and the Kinetic Molecular Theory 8.2 First Law of Thermodynamics: Heat, Work, Internal Energy, and Enthalpy 8.3 Second and Third Laws of Thermodynamics: Entropy, Carnot Engine, and Absolute Entropies 8.4 Gibbs and Helmholtz Free Energy, Spontaneity, and Fundamental Equations 8.5 Chemical Potential, Partial Molar Quantities, Fugacity, and Activity
9 Chapter 9: Physical Chemistry: Equilibrium, Phase Equilibria, Solutions, and Electrochemistry
9.1 Chemical Equilibrium: Equilibrium Constants, Le Chatelier's Principle, and the van 't Hoff Equation 9.2 Phase Rule, Phase Diagrams of One- and Two-Component Systems, and Clausius-Clapeyron Equation 9.3 Solutions: Raoult's and Henry's Laws, Colligative Properties, and Electrolytes 9.4 Electrochemistry: Galvanic Cells, Standard Potentials, and the Nernst Equation 9.5 Electrolyte Conductance, Ionic Mobility, Transport Numbers, and Concentration Cells
10 Chapter 10: Physical Chemistry: Kinetics, Surface Chemistry, and Quantum Mechanics
10.1 Reaction Rates, Rate Laws, and Integrated Rate Equations 10.2 Temperature Dependence of Rates: Arrhenius Equation, Collision Theory, and Transition State Theory 10.3 Reaction Mechanisms: Steady-State Approximation, Chain Reactions, and Catalysis 10.4 Surface Chemistry, Adsorption Isotherms, Colloids, and Macromolecular Solutions 10.5 Postulates of Quantum Mechanics, Operators, Particle in a Box, and Harmonic Oscillator 10.6 Atomic Spectra, the Hydrogen Atom, Many-Electron Atoms, and Term Symbols
11 Chapter 11: Organic Chemistry: Structure, Stereochemistry, and Hydrocarbons
11.1 Systematic IUPAC Nomenclature and Conformational Analysis of Alkanes and Cycloalkanes 11.2 Stereochemistry: Chirality, Enantiomers, Diastereomers, (R)/(S) Configuration, and Optical Activity 11.3 Alkenes and Alkynes: Addition Reactions, Markovnikov Rule, and Stereospecificity 11.4 Aromaticity: Hückel's Rule, Electrophilic Aromatic Substitution, and Directing Effects
12 Chapter 12: Organic Chemistry: Functional Groups, Mechanisms, Synthesis, and Structure Elucidation
12.1 Nucleophilic Aliphatic Substitution ($S_N1$, $S_N2$) and Elimination ($E_1$, $E_2$) Mechanisms 12.2 Alcohols, Phenols, Ethers, and Epoxides: Structure, Synthesis, and Reactivity 12.3 Carbonyl Compounds I: Aldehydes and Ketones, Nucleophilic Addition, and Oxidation/Reduction 12.4 Carbonyl Compounds II: Carboxylic Acids and Derivatives, Enolate Chemistry, and Condensations 12.5 Amines: Basicity, Synthesis, Reactions, and Arenediazonium Chemistry 12.6 Structure Elucidation: NMR Spectroscopy, Combined Spectral Problems, and Qualitative Organic Tests 12.7 Organic Synthesis Strategy, Protecting Groups, Rearrangements, and Pericyclic Reactions
13 Chapter 13: Biochemistry: Cells, Biomolecules, Enzymes, and Membranes
13.1 Cells, Organelles, Water, and Biological Acid-Base Buffers 13.2 Amino Acids, Peptides, and Hierarchical Protein Structure 13.3 Protein Purification and Biochemical Analysis of Proteins, Carbohydrates, and Lipids 13.4 Enzyme Nomenclature and Classification, Cofactors, Coenzymes, and Vitamin Precursors 13.5 Enzyme Kinetics: Michaelis-Menten Model, Lineweaver-Burk Analysis, and Enzyme Inhibition 13.6 Carbohydrates, Lipids, Biological Membranes, and Membrane Transport
14 Chapter 14: Biochemistry: Metabolism, Bioenergetics, Photosynthesis, and Molecular Genetics
14.1 Carbohydrate Catabolism and Anabolism: Glycolysis, Gluconeogenesis, Glycogen, and Pentose Phosphate Pathway 14.2 Citric Acid Cycle, Mitochondrial Electron Transport, Oxidative Phosphorylation, and $\beta$-Oxidation 14.3 Photosynthesis: Light Reactions, Photophosphorylation, and the Calvin Cycle 14.4 Lipolysis and Lipid Biosynthesis: Fatty Acids, Triacylglycerols, and Cholesterol 14.5 Nitrogen Metabolism: Nitrogen Fixation, Amino Acid Metabolism, and the Urea Cycle 14.6 Nucleic Acids, DNA Replication, Transcription, Translation, and Recombinant DNA Techniques 14.7 Regulation of Gene Expression, Mutation and Mutagens, DNA Repair, Carcinogenesis, and cDNA Cloning
5.1 Analytical Measurements: Apparatus, Units, Concentration, Sampling, and Sample Preparation
Key Takeaways Explain This Topic AI
Class A volumetric glassware has tight tolerances: about +/-0.03 mL for a 25 mL pipet, +/-0.05 mL for a 50 mL burette, and +/-0.08 mL for a 100 mL volumetric flask.
Concentrated reagent molarity equals density x 1000 x mass fraction / molar mass, so 37.2% HCl (1.19 g/mL) is about 12.1 M and 96% H2SO4 (1.84 g/mL) about 18.0 M.
When a sample is diluted to volume and only an aliquot is titrated, multiply the aliquot result by the total volume divided by the aliquot volume.
Total variance is the sum of the sampling and method variances; once the method standard deviation is below about one-third of the sampling standard deviation, improving the method barely helps.
In the Philippines, ISO/IEC 17025 laboratory accreditation is granted by the DTI Philippine Accreditation Bureau, while the DOST-ITDI National Metrology Laboratory maintains national measurement standards.
Last updated: October 2026
5.1 Analytical Measurements: Apparatus, Units, Concentration, Sampling, and Sample Preparation
Quick Answer: Analytical area A (10 items) covers basic concepts: instruments and apparatus, laboratory safety and disposal (Section 1.3), units, and stoichiometric, concentration, dilution, and aliquot calculations. Area B adds sampling and sample preparation, significant figures, and standards organizations. These calculations sit inside almost every quantitative question, so practise them until they are automatic.
- Weighing and Volumetric Apparatus
- The Analytical Balance
A standard analytical balance reads to 0.1 mg; semimicro balances read to 0.01 mg.
Weighing by difference (weigh the container, transfer the sample, reweigh) avoids exposing hygroscopic solids and cancels constant balance errors.
Dry primary standards in an oven (typically 105-110 C) and cool them in a desiccator before weighing. Never weigh warm objects: convection currents make them read light.
A buoyancy correction matters for low-density samples: W = W ′ + W ′ ( d a i r d o b j − d a i r d w t s ) W = W' + W'\left(\frac{d_{air}}{d_{obj}} - \frac{d_{air}}{d_{wts}}\right) W = W ′ + W ′ ( d o bj d ai r − d wt s d ai r ) , with d a i r ≈ 0.0012 d_{air} \approx 0.0012 d ai r ≈ 0.0012 g/mL and d w t s = 8.0 d_{wts} = 8.0 d wt s = 8.0 g/mL for steel weights.
Volumetric Glassware
Item Calibration Class A Tolerance (Typical Size)
Volumetric (transfer) pipet To deliver (TD) ± 0.03 \pm 0.03 ± 0.03 mL (25 mL); ± 0.02 \pm 0.02 ± 0.02 mL (10 mL)
- Burette To deliver (TD) ± 0.05 \pm 0.05 ± 0.05 mL (50 mL)
- Volumetric flask To contain (TC) ± 0.08 \pm 0.08 ± 0.08 mL (100 mL); ± 0.12 \pm 0.12 ± 0.12 mL (250 mL)
- Graduated cylinder, beaker Approximate only Not for quantitative work
Read the bottom of the meniscus at eye level to avoid parallax . Rinse pipets and burettes with the solution they will hold, never with water alone. Calibrate glassware by weighing the water it delivers: at 25 C, 1.0000 g of water weighed in air with steel weights corresponds to 1.0040 mL.
Units and Concentration
The SI has seven base units: metre, kilogram, second, ampere, kelvin, mole , and candela. Since 2019 all seven are defined by fixed constants.
- Expression Definition Comment
- Molarity, M mol solute / L solution Changes slightly with temperature
- Molality, m mol solute / kg solvent Temperature-independent; used for colligative properties
- Formality, F formula weights / L Used for salts without regard to dissociation
- Normality, N equivalents / L Depends on the reaction; IUPAC discourages it
- Mass percent, % w/w g solute / 100 g sample Concentrated reagents
ppm, ppb 10 − 6 10^{-6} 1 0 − 6 , 10 − 9 10^{-9} 1 0 − 9 mass fractions In dilute water, 1 ppm is about 1 mg/L and 1 ppb about 1 µg/L
p-function p X = − log [ X ] pX = -\log[X] pX = − lo g [ X ] pH, pCa, pAg
Concentrated reagent molarity:
M = ρ ( g/mL ) × 1000 × w molar mass M = \frac{\rho\ (\text{g/mL}) \times 1000 \times w}{\text{molar mass}} M = molar mass ρ ( g/mL ) × 1000 × w
For 37.2% HCl with density 1.19 g/mL, M = 1.19 × 1000 × 0.372 36.46 = 12.1 M = \frac{1.19 \times 1000 \times 0.372}{36.46} = 12.1 M = 36.46 1.19 × 1000 × 0.372 = 12.1 M. Concentrated H 2 S O 4 H_2SO_4 H 2 S O 4 (96%, 1.84 g/mL) is 18.0 M.
Unit conversion: 2.5 ppm Fe in water is 2.5 mg/L, which equals 2.5 × 10 − 3 55.845 = 4.5 × 10 − 5 \frac{2.5 \times 10^{-3}}{55.845} = 4.5 \times 10^{-5} 55.845 2.5 × 1 0 − 3 = 4.5 × 1 0 − 5 M.
- Dilutions and Aliquots
- C 1 V 1 = C 2 V 2 C_1V_1 = C_2V_2 C 1 V 1 = C 2 V 2
For serial dilutions , multiply the dilution factors: three successive 1-to-10 dilutions give 1-to-1000.
Worked aliquot problem: A 0.4000 g iron ore sample is dissolved, reduced to F e 2 + Fe^{2+} F e 2 + , and diluted to 250.0 mL. A 25.00 mL aliquot needs 12.40 mL of 0.004000 M K M n O 4 KMnO_4 K M n O 4 ( M n O 4 − + 5 F e 2 + + 8 H + → M n 2 + + 5 F e 3 + + 4 H 2 O MnO_4^- + 5Fe^{2+} + 8H^+ \rightarrow Mn^{2+} + 5Fe^{3+} + 4H_2O M n O 4 − + 5 F e 2 + + 8 H + → M n 2 + + 5 F e 3 + + 4 H 2 O ).
mol M n O 4 − MnO_4^- M n O 4 − = 0.01240 × 0.004000 = 4.960 × 10 − 5 = 0.01240 \times 0.004000 = 4.960 \times 10^{-5} = 0.01240 × 0.004000 = 4.960 × 1 0 − 5
mol F e Fe F e in the aliquot = 5 × 4.960 × 10 − 5 = 2.480 × 10 − 4 = 5 \times 4.960 \times 10^{-5} = 2.480 \times 10^{-4} = 5 × 4.960 × 1 0 − 5 = 2.480 × 1 0 − 4
mol F e Fe F e in the sample = 2.480 × 10 − 4 × 250.0 25.00 = 2.480 × 10 − 3 = 2.480 \times 10^{-4} \times \frac{250.0}{25.00} = 2.480 \times 10^{-3} = 2.480 × 1 0 − 4 × 25.00 250.0 = 2.480 × 1 0 − 3
%Fe = 2.480 × 10 − 3 × 55.845 0.4000 × 100 = 34.62 % = \frac{2.480 \times 10^{-3} \times 55.845}{0.4000} \times 100 = 34.62\% = 0.4000 2.480 × 1 0 − 3 × 55.845 × 100 = 34.62%
Significant Figures
Addition and subtraction: keep the fewest decimal places: 12.11 + 0.3 = 12.4 12.11 + 0.3 = 12.4 12.11 + 0.3 = 12.4 .
Multiplication and division: keep the fewest significant figures: 3.141 × 2.1 = 6.6 3.141 \times 2.1 = 6.6 3.141 × 2.1 = 6.6 .
Logarithms: the digits after the decimal point in the log equal the significant figures in the number. [ H + ] = 4.3 × 10 − 5 [H^+] = 4.3 \times 10^{-5} [ H + ] = 4.3 × 1 0 − 5 M (two figures) gives pH 4.37; going back, pH 4.37 gives [ H + ] = 4.3 × 10 − 5 [H^+] = 4.3 \times 10^{-5} [ H + ] = 4.3 × 1 0 − 5 M.
Exact numbers (stoichiometric coefficients, defined conversions) do not limit significant figures. Round only at the end, carrying at least one extra digit through intermediate steps.
Sampling
An analysis can be no better than its sample. The sampling chain runs from the population (lot) to a gross sample , then a laboratory sample , and finally the test portion actually analysed.
Random sampling gives every portion an equal chance of selection. Systematic (grid or time-interval) sampling is practical but can miss periodic variation. Composite samples average a lot; discrete samples reveal its variability.
Heterogeneous solids are reduced by coning and quartering or with a riffle splitter , and ground to a uniform particle size.
Variance adds: s o v e r a l l 2 = s s a m p l i n g 2 + s m e t h o d 2 s_{overall}^2 = s_{sampling}^2 + s_{method}^2 s o v er a ll 2 = s s am pl in g 2 + s m e t h o d 2 . With 3% sampling and 1% method standard deviations, the overall value is 9 + 1 = 3.2 % \sqrt{9 + 1} = 3.2\% 9 + 1 = 3.2% . Halving the method error to 0.5% only lowers it to 3.0%, so collecting better samples is the priority.
The number of samples needed for a target error e e e is approximately n = t 2 s s 2 e 2 n = \frac{t^2 s_s^2}{e^2} n = e 2 t 2 s s 2 .
Preserve samples appropriately: acidify water to pH below 2 for metals, refrigerate for nutrients and BOD, and avoid contamination from containers.
Sample Preparation and Dissolution
- Approach Used For Notes
- Drying and grinding Solids Report on a dry basis or state moisture separately
Acid dissolution ( H C l HCl H Cl , H N O 3 HNO_3 H N O 3 , aqua regia) Metals, alloys, carbonates Aqua regia (3 HCl : 1 H N O 3 HNO_3 H N O 3 ) dissolves Au and Pt
H F HF H F Silicates Extremely hazardous; needs calcium gluconate first aid
Closed-vessel microwave digestion Biological and environmental samples Fast, retains volatile elements, low contamination
Wet ashing ( H N O 3 HNO_3 H N O 3 / H 2 S O 4 H_2SO_4 H 2 S O 4 , H 2 O 2 H_2O_2 H 2 O 2 ) Organic matrices H C l O 4 HClO_4 H Cl O 4 only with H N O 3 HNO_3 H N O 3 present and a perchloric-rated hood
Dry ashing in a muffle furnace Organic matrices Simple, but volatile elements (Hg, As, Se) may be lost
Fusion with fluxes ( N a 2 C O 3 Na_2CO_3 N a 2 C O 3 , L i B O 2 LiBO_2 L i B O 2 , K 2 S 2 O 7 K_2S_2O_7 K 2 S 2 O 7 ) Refractory oxides, silicates Molten flux at high temperature
Kjeldahl digestion ( H 2 S O 4 H_2SO_4 H 2 S O 4 , catalyst) Organic nitrogen Converts N to N H 4 + NH_4^+ N H 4 + before distillation
Standards Organizations and Accreditation
International: ISO (standards, including ISO/IEC 17025 for testing and calibration laboratories); IUPAC (nomenclature and terminology); BIPM (the SI); NIST (Standard Reference Materials); AOAC INTERNATIONAL (official food and agricultural methods); ASTM International; APHA, AWWA, and WEF ( Standard Methods for the Examination of Water and Wastewater ); the USP (pharmaceutical monographs); US EPA methods; and Eurachem/CITAC guides on method validation and measurement uncertainty.
Philippines: the DTI Philippine Accreditation Bureau (PAB) accredits laboratories to ISO/IEC 17025. The DTI Bureau of Philippine Standards issues Philippine National Standards (PNS). The National Metrology Laboratory at DOST-ITDI maintains national measurement standards.
Certified reference materials (CRMs) with traceable certified values are used to establish accuracy and metrological traceability; Section 1.3 covers the quality system.