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Chemical Measurements Chapter 1

Carbon fiber electrode (dia.=100 nm) Dopamine detection Biochemical Measurements with a Nanoelectrode. Neurotransmitter detection (in vitro & in vivo)

Some important units of measurement 1-1. SI units (Le Système International d'Unités): International System of Units 1960’ 11 th (CGPM, Conférence Générale des Poids et Mesures) -> "SI ＂ Fundamental SI unit: 7

Examples: 1.7 x 10 4 m x 1km/10 3 m = 17 km 0.019Pa x 1mPa/10 -3 Pa =19mPa Using prefixes as multipliers *** Rather than using exponential notation, we often use prefixes from Table 1-3 to express large or small quantities.

Converting between units *** Although SI is the internationally accepted system of measurement in science, other units are encountered. Useful conversion factors are found in table 1-4.

Solution: a homogeneous mixture of two or more substance; it composed of Solute ( a minor species) and Solvent ( the major species) ▶ mol : Avogadro number of particles. Molarity (M): the number of moles of a substance per liter of solution. ▶ (6.022 Х ) :1mol ▶ (molar mass, M ), 1mol mass ( g) n x : number of mol of x, M x : mole mass(g/mol) of x mass x : mass(g) of x 1-2. chemical concentrations Def:The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in kilogram of carbon 12; its symbol is "mol.“

Ex) Molecular mass( M ): The sum of atomic mass. Formaldehyde(CH 2 O) and glucose(C 6 H 12 O 6 ) moles?

■ Analytical molarity (mol/L) ■ Equilibrium molarity (mol/L) Formal concentration (F) = (mass/ formula mass) /L Ex) In case of electrolyte (strong & weak electrolytes)

solution(L) solute(mol) Molarity (M) = ( ☞ M = mol/L = mmol/mL) Formal concentration (F) = - Formula mass (FM): molecular mass of a strong electrolyte ☞ F : Molarity of strong electrolyte for the original chemical formula in solution solution(L) solute(mol) Molality (m) = solvent(Kg) solute(mol) (independent of T) M =M = V mol mol = MV Example Molarity of Salts in the Sea (a) Sea water contains 2.7 g of NaCl per 100 mL (0.1 L) → molarity(M)? (b) M MgCl 2 → g of MgCl 2 in 25 mL? Solution (a) Molar mass of NaCl = g/mol Moles of NaCl = 2.7/22.99 = mol ∴ Molarity (M) = mol/ 0.1 L = 0.46 M (b) Molar mass of MgCl 2 = g/mol ∴ x = 0.13 g M =M = V mol L x g/95.20 gmol -1 = M =

Weak electrolyte * Molality (m) is concentration expressed as moles of substance per kilogram of solvent. Equilibrium is dependent on the temperature.

Percent concentration (%) Solution = solute + solvent

Parts per Million and Parts per Billion ppm for aqueous solution: ppb for aqueous solution: mg L μg L = μg mL = ng mL ppm = solute solution × 10 6 ppb = solute solution × g of water equates with 1 ml of water approximately. ( 1 ppm = 1 μg/mL)

1-3 preparing solutions To prepare a solution with a desired molarity from a pure solid or liquid, we weigh out the correct mass of reagent and dissolve it in a volumetric flask.

Solution-diluent volume ratios 진한용액의 부피 : 묽히는 용액의 부피 = A : B ⇒ 1 : 4 HCl 용액 = 진한 HCl 부피 부피의 물 p-function

Check the density of commercial reagents in liquid.

Stoichiometry is the calculation of quantities of substances involved in a chemical reaction

1-4 Stoichiometry calculations for Analysis Chemical analysis based on weighing a final product is called gravimetric analysis. Experimental procedure: Step 1: Preparation of sample solution. Step 2: Chemical reaction to a species. Step 3: Convert the species to stable final product.

Fe 2+ C 4 H 2 O inert binder Fe 2+ C 4 H 2 O inert binder Step 1,2,3 Fe 2 O 3 Step 1. Dissolve the Fe 2+ with HCl Step 2. Oxidation of Fe 2+ to Fe 3+ with H 2 O 2 2Fe 2+ + H 2 O 2 + 2H + → 2Fe H 2 O (1-5) Step 3. Precipitate hydrous iron(III) oxide with NH 4 OH filter and ignite to convert it to pure solid Fe 2 O 3 Fe OH - +(x-1)H 2 O → FeOOH ㆍ xH 2 O(s) → Fe 2 O 3 (1-6) 900 ℃ 1Fe 2Fe Ex) Iron measurement in tablet by gravimetric analysis (Mass ? ) Sample(tablet) g of Fe in tablet?

1-5. Introduction to titrations Procedures in which we measure the volume of reagent needed to react with analyte (the sub-stance being measured) are called volumetric analysis. titration, titrant (reagent solution), equivalent point, end point indicator, titration error, blank titration, primary standard, standardization standard solution, direct titration, back titration Gravimetric titration

⇒ End point: appearance of the first trace of purple color of MnO 4 -  Titration error - The difference between the end point of a titration and the equivalence point of it. - The end-point may be slightly different from the true equivalence point.  Blank titration - The same titration procedure without analyte - Can estimate and reduce the titration error ⇒ Equivalence point: occurs when 2 moles of MnO 4 - is added to 5 moles of oxalic acid Procedure for correction of titration error by a blank titration i) repeat titration procedure without analyte ii) determine amount of titrant needed to observe change iii) subtract blank volume from titration (1-7) Ex) Titration of Oxalic acid with KMnO 4 Analyte Oxalic acid (colorless) Titrant (purple) (colorless) 5HO–C–C– OH = = O O + 2MnO H + → 10CO 2 + 2Mn H 2 O

Primary standard Standard solution - a solution of known concentration (molarity) - use as a titrant Standardization - the process of determining the exact concentration of a solution.  Grade of Chemicals - Reagent-grade chemicals meeting purity requirements set by the American Chemical Society(ACS) Committee on Analytical Reagents. - Primary standard grade. - Trace analysis (analysis of species at ppm and lower levels): impurities in reagent chemicals must be extremely low. BOX 1-1 Reagent Chemicals and Primary Standards Direct titration: add titrant to analyte until the reaction is complete Back titration: add a known excess of one standard reagent to the analyte

1-6 Titration Calculations In stoichiometry calculations in volumetric analysis, the key step is to relate moles of tyrant to moles of analyte. Primary standardStandard solutionH2C2O4H2C2O4 (Na 2 C 2 O 4 )(KMnO 4 ) StandardizationTitration