Analytical Chemistry Concepts

• Pharmaceutical Analytical Chemistry II, sections 1 and 2 cover quantitative analysis, ways to express concentration, glasswares, volumetric analysis, and acid-base titrations.

Analysis

• Quantitative and qualitative analysis are two methods of chemical analysis.
• Quantitative analysis consists of gravimetric analysis, volumetric analysis, and instrumental analysis.

Ways to Express Concentration

• Ways to express concentration can me molar, normal, molal, formal, or a percentage
• Mole (gram-molecular weight) refers to the molecular weight of a substance in grams
• One mole of NaOH equals 40g
• 0.5 mole of NaOH equals 20g
• 2 moles of NaOH equals 80g
• The number of moles can be calculated with the formula: No. of moles = Weight "gm"/M.W

Equivalent Weight

• Equivalent Weight refers to the weight of a substance which is chemically equivalent to one gram-atom of protons
• Equivalent Weight can be calculated with the forumla: E.W= M.W/n
• n is for the number of replaceable H+ (Acid) or the number of OH groups (Alkali)
• E.W of HCl = M.W/n = 36.5/1 = 36.5
• E.W of H₂SO₄ = M.W/n = 98/2 = 49
• H₂SO₄ + NaOH →NaHSO₄ + H₂O n=1, E.W = 98/1 = 98
• H₂SO₄ + 2NaOH →Na₂SO₄ + 2H₂O n=2, E.W = 98/2 = 49
• HCl has n=1, H2SO4 has n=2, H₃PO₄ has n=3
• NaOH has n=1, Ca(OH)₂ has n=2, Al(OH)₃ has n=3

Molar Concentration

• A solution of contains one gram-molecular weight of a substance in one liter of solution.
• Molar Concentration = No. of moles/Volume "L"
• No. of moles = Weight "gm"/M.W
• M = Weight "gm" / M.W * volume “L”
• Weight "gm" = M * M.W * volume “L”
• HCl has M.W of 36.5, H2SO4 has M.W of 98, NaOH has M.W of 40, Na2CO3 has M.W of 106, and NaCl has M.W of 58.5

Normal Concentration

• A solution which contains one gram-equivalent weight of the ubstance in one liter of solution.
• Normal concentration = No. of gm equivalents/Volume "L"
• No. of gm equivalents = Weight "gm"/E.W
• E.W = M.W / n
• Weight "gm" = N* E.W * volume “L”
• For HCl, M.W/E.W is 36.5/36.5; for H2SO4, M.W/E.W is 98/49; for NaOH, M.W/E.W is 40/40; for Na2CO3, M.W/E.W is 106/53; and for NaCl, M.W/E.W is 58.5/58.5
• Normal concentration = No. of gm equivalents/Volume "L"
• N = Weight "gm"/ E.W * volume “L”
• N = Weight "gm"* n/ MW*volume“L”
• The following is true: N = M*n

Percentage

• Percentage Concentration = weight (g)/Volume (mL) x 100

Glasswares

• Glasswares can me volumetric or other
• Volumetric Glasswares are burettes, pipettes, and volumetric flasks
• Other glasswares are conical flasks, and beakers

Volumetric Analysis

• It's the process of bringing a measured volume of a standard solution (Titrant) into a quantitative reaction with the substance to be deteremined (Analyte)
• Types of titration are acid-base (neutralization) titration; precipitation titration; complex formation titration; redox titration

Acid-Base Titration

• NaOH + HCl → NaCl + H₂O is an example acid-base titration
• The equation: HCl + NaOH -> NaCl + H₂O is an example reactions with solute and known stoichiometry
• The point at which a reaction between the titrant and analyte has just completed is the end, or eqiuvalence point
• The equivalence point indicated by change in the color of an indicator
• At E.P, the number of moles of titrant is equal to the number of moles of analyte
• The number of moles of NaOH= number of moles of HCl
• To calculate no of moles: MXV (NaOH) = M'V' (HCI)
• To calculate concentration M = No of moles/ V (L)
• N.V = N'.V'

Titre

• The weight of analyte chemically equivalent to 1 ml of the titrant
• The number of milliliters of titrant equivalent to 1 gm of the sample
• Titre = E.W(sample) × N. (titrant) / 1000

Percentage Concentration Using E.P

• Percentage conc. = Mass of solute (g)/Volume of solution (mL) × 100
• Percentage conc. = E.P × equivalence/ Volume taken (mL) × 100
• E.P is the volume of titrant equivalent to the sample

Indicator in Acid-Base Titration

• An organic compound shows clear visual change when a reaction is completed and it changes color
• Acids and bases are substances which have two colors: one in an acidic medium and another in alkaline conditions
• These are pH indicators, also known as as acid-base indicators
• Phenolphthalein is colorless in acidic medium and pink in alkaline medium
• Methyl orange is orange in acidic medium and yellow in alkaline medium
• Titrant gets added until there is an abrupt change of the indicator to show that all analyte has been consumed: "End point or Equivalence point: E.P"
• During the reaction 10 ml HCl + 2 dps ph.ph reacts with 0.1N NaOH soln until it forms NaCl + 2 dps ph.ph
• C* V acid = C' * V' base

Standard Solution

• A solution that has accurately known concentration.
• Standard solutions are primary or secondary.
• Primary solutions are prepared by direct weighing of a known amount of a primary standard substance, dissolved in a solvent to reach prescribed volume.
• Secondary Solutions are prepared by of non-primary standard substance, which cannot be prepared by direct weighing, so it needs standardization.

Primary Standard Substance

• A substance of sufficient purity from which a primary standard solution can be directly prepared by weighing and dissolving in solution.
• It must meet requirements of absolute or high purity, stability at high temperature, stability when exposed to air; undergoes a fully quantitative reaction; have high equivalent weight to reduce weighing errors; and availability at reasonable cost and nontoxic

Primary Standard Substance Examples

• Acidic examples include CooH, CooH, and Oxalic acid * 2 (H₂O) as well as NH₂-SO3H Sulfamic acid, C₆H₅COOH Benzoic acid, and Potassium hydrogen phthalate
• Alkaline examples are Na₂CO₃, KHCO₃, Na2B4O7.10H2O Borax and COONa, COONa Sodium oxalate

Secondary Standard Solution

• Solution of non-primary standard substance.
• To standardize solution of secondary standard: perform titration against primary or standardized secondary solution; or gravimetric analysis.

Preparation and Standarization

• To prepare 1N SOD. HYDROXIDE weigh 40 gm to and dissolve in 1L D.W (Exact N is ??)
• Standaridze HCl solution with Na2CO3 ; or Oxalic asid primary standard solution to get Exact Normality

Calculations

• Calculation of EXACT normality: N. V acid = N'. V' base
• Calculation of Correction Factor: Desired Normality F = Determined Normality /
• Standardize 0.1N NaOH by Standardized 0.1N HCI following these steps: fill burette with 0.1N HCl; take 10 ml of NaOH in a conical flask with pipette; add 2 drops ph.ph indicator in the flask; start titration with HCl till the colour of the indicator changes from pink to colorless (E.p).
• In the reaction, the eye's position must level with the surface of liquid for accurate measurement.
• N. V HCI = N'. V' NaOH
• 0. 1 X E.p(V HCI )= N' X10 ml
• F (Correction Factor) = Determined Normality / Desired Normality = N/ 0.1

Test your knowledge of analytical chemistry with questions covering qualitative and quantitative analysis. Topics include identifying sample components, molarity, molecular weight, and titration techniques. Enhance your understanding of chemical measurements and reactions.