Analytical Laboratory Techniques PDF

II. Introduction to Analytical Laboratory - After Completing Mass Measurement, Techniques return the mass settings to the zero position A. How to properly clean glassware. E. Proper way of mixing solutions in a test t...

II. Introduction to Analytical Laboratory - After Completing Mass Measurement, Techniques return the mass settings to the zero position A. How to properly clean glassware. E. Proper way of mixing solutions in a test tube. - Clean glasswares before and after 1) Stir the solution with stirring rod experiment 2) Agitate the solution by tapping the side of - Clean with Soap and detergent using brush the test tube or sponge 3) Stoper the test tube and invert, never use - After rinsing with tap water, rinse it one or thumb twice with small amount of distilled water 4) Use Vortex Mixer - Roll each rinse around th entire inner surface go the glass wall for complete rinse, F. Familiarization on the proper ways of discard through the delivery tip transferring liquids and solutions from a - Distilled / Deionized water should be never reagent bottle. used for washing (only for final rinsing) - Remove the glass stopper and hold it in - After washing, Invert in tissue/ mat. Do not between fingers. Never lay it on the table wipe or blow dry, because of possible (possible contamination) contamination. - The glassware is considered as clean if, no water droplets adhere to the clean part B. Preparation of Solutions - From Solid (Molarity) Mol of Solute / L of Solution - From a more concentrated solution (Dilution) M1V1 = M2V2 - If it has screw cap, it can be placed on teh (M1 is always the more concentrated) table upside down. - To transfer liquid, hold a stirring rod against C. Measuring mass the lip of the vessel containing the liquid and - Laboratory Balance pour the liquid down the stirring rod - Most used and abused piece of touching the inner wall of the receiving equipment in the Laboratory vessel. (Rubber Policeman) - Top Loading : 0.01 or 0.001 - Analytical Balance : 0.0001 - Tared Mass - Called to the Resultant Mass of the sample D. Guidelines on using the analytical balance and the top loading blance - Handle with care - If not balance, see lab instructor - Use weighing medium (paper, beaker) - Do not return any excess or unused liquid to - Do not place chemicals directly to the pan the original reagent bottle. - Do not drop anything to the pan - If not properly working, call Lab Instrcutor G. Decantation – process of separating a liquid - Do not attempt to fix it yourselves and a solid mixture. - LIquid = Supernatant / Decante H. Proper Way of Reading a Meniscus 1,. Mohr – Calibration marks do not extend to the - Measurements in Graduated Cylinders, tip. Transfer and dispense liquids up to the Pipette, Buret, and Volumetric Flask should last graduation mark before the tip. be read at the bottom of its meniscus. 2.. Serological – Calibration marks extend all the - If it is a organic solvent, the upper meniscus way to the tip; Transfer and dispense liquids up should be read to the end of the tip. - Position the Eye horizontally at the bottom of the meniscus to read the level of the liquid J. Titration – a quantitative method of determining the concentration of an unknown solution I. Different types of pipets and their uses: (analyte) by reacting it with a solution of known i. Volumetric pipets – Transfer and concentration (titrant). dispense a single, specific quantity of liquid to a very high degree of Accuracy. K. Glassware and equipment needed for titration ii. Micropipettes – transfer and measure - Buret, buret clamp, iron stand, Erlenmeyer small volumes of liquid in microliter, µL flask l. Proper use of buret - operate stopcock with left hand (if right-handed) and swirl the Erlenmeyer flask with your right hand.. iii. Graduated pipets – Type of pipettes with graduation or markings along the tube. III. Quantitative Solution Preparation - Dilution and dilution formula – the process of preparing a less concentrated A. Quantitative Preparation solution from a more concentrated solution. - refers to the precise and accurate - Aliquot – a portion of a solution taken as a preparation of chemical solutions with the representation of the whole solution with the use of volumetric glassware. assumption that the composition of the aliquot is identical to the composition of the B. Study Molarity, moles and percent original solution. concentration calculation. - Molarity 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 - Molality 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝑘𝑔 𝑜𝑓 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 - Percent Concentration Mass Percent 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 ( 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 )𝑥100 Volume Percent 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 ( 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 )𝑥100 Sample Problem : Mass Percent : You dissolve 10 grams of salt (NaCl) in 90 grams of water. What is the mass percent of the salt solution? - Total mass = mass of solute + mass of solvent = 10g + 90g = 100g 10𝑔 - Mass percent = ( 100𝑔 ) 𝑥 100 = 10% Volume Percent: You mix 30 mL of ethanol with 70 mL of water. What is the volume percent of ethanol in the solution? - Total volume = volume of solute + volume of solvent = 30ml + 70ml = 100ml 30𝑚𝑙 - Mass percent = ( 100𝑚𝑙 ) 𝑥 100 = 30% C. Definition of Terms - Solution – a homogenous mixture composed of two or more substances. - Concentration – the amount of solute present in a given amount of solvent or solution. - Stock solution – a concentrated solution that is prepared by weighing out an appropriate portion of a pure solid and stored to be diluted to lower concentrations. IV. Statistical Data Sampling V. Equilibrium and Le Chatelier’s Principle A. Proper use of Analytical Balance A. Equilibrium - Accurate up to 0.0001 gram - The rate of the forward reaction and the rate - Easily be affected by air currents, of the backward reaction are equal. temperatures, humidity, and vibrations, - The concentration of the [reactants] and reasons that require that it be placed in a [products] are constant. climate controlled environment. - Since both reactions occur at the same rate, there is no net change in the concentrations B. Use of Students’s T test of the reactants or of the products. - T-Test : test to measure difference in scores between two groups B. Le Chatelier’s Principle - 3 Types - when a system at equilibrium is disturbed, - Type 1 : One Sample T Test the system will shift to the direction where it - Type 2 : Independent 2-sample re-establishes its equilibrium condition. T-test - Shift to the Right = Shift Towards Product - Type 3 : Dependent Sample or - Shift to the Left = Shift Towards Reactant Paired Sample T Test - Endothermic Reaction - One-Sample T-Test: Compares a sample - Heat is the Reactant mean to a known population mean. - Heat is Absorbed - Independent Two-Sample T-Test: - System will shift towards the product Compares means from two independent - Exothermic Reaction groups. - Heat is the Product - Dependent (Paired) Sample T-Test: - Heat is Release Compares means from two related groups - System will shift towards the (e.g., before and after an intervention). reactant - - If more than 2 groups, ANOVA or Analysis C. Different factors that can disturb the of Variance is used equilibrium condition of a system VI. Complexometric determination of Water - Hard water - water that contains high Hardness concentration of dissolved minerals primarily Calcium and Magnesium A. Study the stoichiometric calculation of water hardness C. Why are phosphates added to soap? - Calculation of Ca2+ in Molarity, ppm. - Phosphates are added to soap and Molarity = 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑎2+ detergents because they bind with calcium 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝐿 𝑚𝑎𝑠𝑠 and magnesium in water preventing them Moles = 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 from forming precipitates with soap, thereby improving the soap’s cleaning effectivity. 2+ Example : Given: 0.80 grams of 𝐶𝑎 in 2.0 liters of solution 2+ 0.80𝑔 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑎 = 40.08𝑔/𝑚𝑜𝑙 = 0. 02 0.02 𝑚𝑜𝑙 𝑀𝑜𝑙𝑎𝑟𝑖𝑟𝑡𝑦 (𝑀) = 2.0𝐿 = 0. 01𝑀 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐶𝑎2+ (𝑚𝑔) 6 Ppm = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝐿 𝑥 10 1) Convert the mass of calcium ions to milligrams. (1g = 1000mg) - 0.80 g = 800 mg 2) Calculate ppm 800𝑚𝑔 6 𝑝𝑝𝑚 = 2.0𝐿 𝑥10 = 400𝑝𝑝𝑚 B. Definition of Terms - EDTA – a hexadentate ligand that binds to metals to form very stable complexes in a 1:1 ratio. - Chelating – is a process by which a ligand (chelating agent) binds to a metal ion forming a stable complex known as chelate. - Titrant – a solution of known concentration in a titration. - Analyte – a substance or solution to be analyzed. (Unknown) - Endpoint – (signal / indication)a point in a titration where the indicator changes color, and that the titration should stop. - Equivalence point – a theoretical point in a titration wherein the amount of the titrant added and reacted is stoichiometrically equivalent to the amount of the analyte in the sample. - Indicator – (EBT ( Eriochrome Black T) for EDTA Titration) – substances that change color when the endpoint is reached. VII. Determination of Iron Content by Redox - a solution whose concentration is accurately Titration known A. Definition of Terms G. Indicator? - Redox Titration – a type of titration that - KMnO4 acts as a self-indicator involves oxidation and reduction where - Since permanganate ion is deep purple and electrons are transferred between reactants the manganese ion is almost colorless, the to determine the concentration of an permanganate ion acts as an internal analyte. indicator showing the titration endpoint - Oxidation – a chemical reaction in which a when a faint pink color persists in the substance loses electrons; Increase in the solution. oxidation state. - Reducing agent – a substance that H. End point color donates electrons to another substance - faint pink color and gets oxidized. - Reduction – a chemical reaction in which a substance gains electrons; Decrease in the oxidation state. - Oxidizing Agent – a substance that accepts electrons from another substance and gets reduced. B. Study Redox Titration Calculation for Fe Content in mg of an Iron Pill Sample - Note the Volume - Calculate Moles of KMnO4 (Conc x Vol) - Calculate Moles of Fe2+ (Moles of KMnO4 x 5) 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐹𝐸2+ - Concentration of Fe2+ ( 𝐿 ) - Mass of Fe (Concentration x L x MM) - Mass in mg (x1000) C. Calculation of % Error, Study the formula 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 − 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 =( 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 ) 𝑥 100 D. The titrant used: KMnO4 - Strong Oxidizing agent that reacts with Iron (II) ion in an acidic solution to quantitatively form the iron (III) and manganese (II) ion - It is very reactive, this is why solution containing this ion must be standardized using a known primary standard before use E. Ferous Ammonium Sulfate Hexahydrate - standard solution used for the standardization of KMnO4 F. Standard solution  D. Different Components of a Spectrophotometer - Light Source : generates a broadband of electromagnetic radiation across the UV visible spectrum (UV Visible Spectro has a VIII. Introduction to Spectrophotometry Xenon flash lamp) - Diffraction Grating : separates the A. Study the Electromagnetic Spectrumno broadband radiation into wavelength - Sample Area : where the light passes through or reflects off a sample - Rotating Mirror : directs the optics into the sample and the sensor - Detectors : measure and compare the transmitted radiation E. How to Use the Spectrophotometer F. Why are gloves and tissue paper used to hold B. Definition of Terms and wipe cuvettes? - Spectroscopy – the study of the interaction – To prevent the transfer of oil, dirt, and other of matter and radiation. contaminants from the hands. - Absorbance – the measure of the amount – To protect the analyst from any potential chemical of light absorbed by the sample. hazards. - Transmittance – the measure of the – To remove fingerprints, smudges or dust that may amount of light that passes through the lead to inaccurate absorbance sample. - Λmax (Lambda Max) - Strongest G. Why is wavelength scanning important? Absorbance – To determine the lambda max of the analyte. - Spectrophotometer - instrument that (Ensures the most precise and reliable results in measures the fraction of the incident light spectrophotometric analysis.) transmitted through a solution. - Cuvette – (cell) a small, rectangular or H. Study the relationship between Absorbance, circular container used in %Transmittance, and Concentration. spectrophotometry to hold liquid samples. - Absorbance is Directly Proportional to - Blank solution – a solution that contains all Concentration the components except the analyte - Transmittance is Inversely Proportional to – a solvent used to dilute/dissolve the Absorbance sample C. Purpose of Blank - To allow for the correction of absorbance or transmittance that is due to the solvent or other components. - It is used to set the instrument to zero absorbance or 100% Transmittance to ensure that only the absorbance or transmittance of the analyte is recorded. - Sets a baseline  e. Determination of the unknown concentration, x using a scientific calculator. 𝑦−𝑎 - 𝑥 = 𝑏 IX. Spectrophotometric determination of Dye a. What is Beer-Lambert’s Law? - Beer-Lambert's Law helps us understand how much light is absorbed by a solution based on how much of a substance is in the solution and how far the light travels through it. - States that the absorbance of a substance is directly proportional to the concentration of the substance in solution - 𝐴 = ε𝑏𝐶 - A = Absorbance - e = Molar Absoptivity - b = Length of Light Path - c = Concentration b. Determination of possible interferences that might affect the absorbance readings. - Sample Preparation Issues - Contaminations (Dirty Cuvettes) c. Calculation of R2 using scientific calculator - Stat Mode - A+Bx - 5 : Reg - 3:r - Add ^2 d. Determination of slope and intercept using a scientific calculator from a given set of data - y = a + bx - a = intercept - b = slope Laboratory Safety a. Safety equipment installed in the laboratory and their uses. b. Familiarization with the basic safety rules in the laboratory. c. Proper waste disposal in the laboratory for hazardous liquid waste, non-hazardous liquid waste, and solid waste. d. The purpose of GHS. e. Hazard classification. f. GHS Pictograms and their meanings. g. Use of Safety Data Sheets and their contents