Experiments in Analytical Chemistry

Transcription

1 University of Thi Qar College of Engineering Petroleum & Gas Engineering Department Experiments in Analytical Chemistry By Associate Khalid Farhod Dr.Professor khaliddr. farhood M.sc Ban Jaber M.sc Maryam Khaleel Eng. Mayada Khalid

2 Introduction The Analytical chemistry laboratory manual for the student of petroleum engineering department include the most important types of chemical glassware with their nomenclature, Chemical Safety in the Laboratory Conduct and describes the experimental procedures with a brief theoretical background and chemical equations. Laboratory Report: 1. Cover Page: Title of the experiment, identify yourself and your partners and Date of Performing the experiment. 2. Purpose or Objective 3. Theoretical Basis. 4. Apparatus and materials required. 5. Results and calculation. 6. Discussion. 7. References. 1

3 Chemical Safety in the Laboratory There are a number of rules that must be followed in order to work safely in a chemical laboratory. Some of these rules are listed below. 1. Always wear your laboratory while working in the laboratory. 2. Always check the label on the bottle before using a chemical reagent. 3. Never taste a chemical or a solution, many laboratories chemical are poisonous 4. Keep your face at a safe distance if your experiment generates an objectionable gas. Work under the suction hood. 5. Don't pick hot objects with your bare hand. If your hand is burned, use some burn ointment 6. Avoid using bare hand in the transfer of chemicals. 7. In the event of malfunction in any tool or device within the laboratory must inform the offices and not repaired by the student. 8. Wash your hands well before leaving the laboratory 9. To avoid spattering of acids which can cause burns, always add acid to water. Never add water to acid. 10. Before obtaining any reagents, carefully read the labels on the bottles twice. Many chemicals have similar names or concentrations may vary. 11. To avoid unnecessary waste, obtain only the amount of chemicals called for in an experiment. Your instructor will tell you the proper procedure for dispensing liquids and solids. Never insert medicine droppers or scoops into reagent bottles. 12. Never return unused chemicals to the original dispensing bottle. 2

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5 Volumetric (Titrimetric) analysis: Volumetric analysis (or Quantitative chemical analysis): Titration is the slow addition of one solution of a known concentration (called a titrant or titrator) to a known volume of another solution of unknown concentration (called a titrand or analyte) until the reaction reaches neutralization, which is often indicated by a color change. The standard solution is usually added from a graduated vessel called a burette. The process of adding the standard solution until the reaction is just complete is termed a titration. The solution of accurately known strength is called the standard solution. The standard solution is usually added from a graduated vessel called a burette. The process of adding the standard solution until the reaction is just complete is termed a titration. The reagent of known concentration is called the titrant, and the substance being titrated is termed the titrand. Equivalent point is the point in a titration where the amount of standard titrant added is chemically equivalent to the amount of analyte in sample. End point is the point in a titration when an observable change that signals of the titrant's amount added is chemically equivalent to the amount of analyte in sample. Indicator is a reagent used to indicate when the end point has been reached. 4

6 A primary standard is a highly purified compound that serves as a reference material in all volumetric titrimetric methods. Important requirements for primary standard compounds are: Extremely pure Highly stable Anhydrous Less hygroscopic High molecular weight relatively Can be weighed easily Should be ready to use and available Should be preferably non toxic Should not be expensive Calculations of volumetric analysis: Molar solution: Normal solution: Part per million (ppm) Equivalent weight: (1)Equivalent weight in neutralization reaction: - Equivalent weight of Acid = molecular weight/ number of H+ Equivalent weight of base = molecular weight/ number of OH- 5

7 (2) Equivalent weight in Oxidation Reduction: The equivalent weight of an oxidant or a reducing is the number of electrons which 1mol of the substance gains or losses in the reaction. (3) Equivalent weight of salt = molecular weight / valency of The metal ion 6

8 Exp. No. Contents Exp.Name Page No. One Two Three Preparation of Standard solution : 1- Primary standard solution 2- Secondary Standard solution Titration Curve Four Five Six Direct Titration Standardization of NaOH Back titration Seven Determination of Hardness of Water 13 Eight Acidity of Vinegar 14 7

9 Primary standard solution: Preparation of Standard solution The primary standard is a highly purified compound that serves as a reference material in volumetric and mass titrimetric methods. The accuracy of a method is critically dependent on the properties of this compound. Important requirements for primary standard are the following: High purity (e.g.99.9%by weight), atmospheric stability, absent of hydrate water, modest cost, reasonable solubility in the titration medium and reasonable large molar mass. One of such compounds is sodium carbonate (Na2CO3). Procedure: To prepare 250ml of 0.1N Sodium carbonate (Na2CO3). Dry Appropriate quantity of sodium carbonate in an oven set at 110 oc for 1hr. Store the dried material in desiccators. Calculate the weight of (Na2CO3) from the law. Weight (Na2CO3) using a microbalance (1.0 or 0.1 mg accuracy). Transfer this quantity into a 250 ml beaker and solve it in about 50ml distilled water (D.W). Transfer the solution into a 250ml volumetric flask. Complete the solution to the mark by distilled water with the same beaker. Stopper the volumetric flask and shake well. 8

10 Secondary Standard solution Some compounds consider as secondary standard solution due missing one of the important requirements for primary standard. For that can prepare as an approximate normal solution and then calibrate with a known standard chemical solution by volumetric analysis. Such as: hydrochloric acid HCL, sodium hydroxide NaOH Procedure: Preparation of approximately (0.1N) HCl from 37% and 1.2 Sp.g Calculate the Normality of the concentrated HCl from the law: To prepare (500ml) of 0.1N HCL: N 1 V 1 = N 2 V 2 N1 *? = 0.1 * 500 Transfer some of distilled water to 500ml volumetric flask and add the calculated volume of conc. HCl. Mix the content thoroughly. Complete to the mark with distilled water and make a label. 9

11 Titration Curve: it is a graph representing the relationship between (ph) for the solution with the volume of the additive in the process of titration. When strong acid as (HCl) titrated against strong base such as (NaOH) both will completely ionize. This means that the (H+) and (OH-) ions be (H 2 O) and other (Na + &Cl - ) remains in solution as ions. Procedure: Put 20ml solution of HCl (0.25M) in the Beaker size (250ml). Fill the burette with (0.1M) NaOH solution. Add two drops of Phenolphthalein (ph.ph.) as an indicator then appointed the ph of the solution (using ph Meter). Add (0.1N) NaOH drop by drop until reaching equivalent point, write the volume then drop another 3 ml of (0.1N) NaOH measure the ph. Direct Titration Standardization of NaOH Two steps used to standardization normality of NaOH First; accurate normality of sodium carbonate to standardize the hydrochloric acid solution as the following reaction: Na2CO3 + HCl = NaHCO3 + NaCl Na2CO3 + HCl = NaCl + H2O + CO2 In this reaction one mole of hydrochloric acid equivalent with sodium carbonate and converted into sodium bicarbonate. The second mole of 10

12 hydrochloric acid converts the produced sodium bicarbonate into sodium chloride, water and carbon dioxide gas which evolves to the atmosphere. The two equations can be assumed and re-written into the following reaction Na2CO3 + 2HCl = 2NaCl + H2O + CO2 Second; titration the standardized HCl with NaOH NaOH + HCl = NaCl + H2O Procedure: A) Standardization of Hydrochloric acid: Transfer 10 ml of 0.1 N Na2CO3 solutions to the 250 ml conical flask by pipette. Add approximately 20ml distilled water to the conical flask and 2-3drops of methyl orange as indicator. Full the burette with hydrochloric acid solution (unknown normality). Titrate the solution dropwise until the pale yellow colored solution converts to orange colored solution. Record the volume of hydrochloric acid. B) Determination the normality of Sodium hydroxide Transfer 10ml of sodium hydroxide solution into a 250ml conical flask by pipette. Add 20ml distilled water and 2-3 drops (ph.ph) indicator. Full the burette with hydrochloric acid standardized solution. 11

13 Titrate dropwise with continuous shaking until one drop of the acid converts the pink color base solution into a colorless solution. Determine the normality of sodium hydroxide solution using the formula: N 1 V 1 =N 2 V 2 Back titration Sometimes reaction is slow to go to completion and a sharp end-point cannot be obtained, aback titration will give a useful results. To calculate a substance like: Procedure: Put 10ml of the acid sample into a 250ml conical flask by pipet Add 10 ml of 0.1N NaOH solution into a 250ml conical flask by pipette. Add 2 drops of phenolphthalein indicator. Titrate against 0.1N HCl acid from a burette until the solution color changes from pink to colorless. Let this volume be V1 ml. Calculate the normality of the acid solution. 12

14 Determination of Hardness of Water Hardness of water, attributed to the presence of Ca +2 and Mg +2 if as HCO 3 and CO 3 salts in water, it can be removed by boiling the water to convert these anion into CO 2 and H 2 O if as SO 4 or Cl it will be hard to be removed. Procedure: 1) Place 100ml of tap water in a 250ml beaker. 2) Heat slowly over a Bunsen burner and then boil gently for 30 minutes 3) Cool the hot water and filter through filtered funnel directly into 250ml conical flask. 4) Add 1ml buffer solution ph=10 to 10ml Sample and then add 0.1g of Eriochrome Black-T Indicator. 5) Titrate against 0.01M EDTA solution from a burette until color changes from red to blue. 4) Add 1ml of (1N) NaOH to 10ml Sample and then add 0.1g of meroxide Indicator and measure the total hardness. 5) Titrate against 0.01M EDTA solution from a burette until color changes from blue to violet and measure the Ca and Mg hardness. Calculate the permanent hardness of water in terms of ppm CaCO 3 Determine temporary hardness in terms of ppm CaCO 3. 13

15 Acidity of Vinegar Vinegar contains about 5%by volume acetic acid CH 3 COOH most of the remaining 95%is water plus small quantities of ethyl alcohol and other carboxylic acid. The acid contents or vinegar may determine quantitatively by volumetric titration with standard solution of sodium hydroxide solution using phenolphthalein indicator. Part (A): Calibrate the solution of NaOH by using standard solution of 0.1N HCl NaOH +HCl = NaCl + H2O Procedure: Transfer 10.0ml of 0.1 N HCl into a clean 250ml. conical flask and 2 drops of phenolphthalein (ph.ph.) indicator. Titrate against sodium hydroxide solution stop titration when the color of solution changes from colorless to pink color. Determine the concentration of CH 3 COOH in vinegar. Calculate the weight of CH 3 COOH. Calculate the percentage of CH3COOH wt/wt % and wt/vol. %. N 1 * V 1 = N 2 * V 2 14

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17 Experiments of Organic Chemistry 16

18 Exp.No One Exp.Name Boiling point determination Page No. 18 Two Melting Point Determination 19 Three Simple Distillation 20 Four Esters and Esterification 21 Five Preparation of acetic acid 22 17

19 UBoiling point determination The boiling point of liquid is a temperature at which the vapor pressure of the liquid is equal to the external pressure exerted at any point upon the liquid surface. U Procedure: 1) Close one end of the capillary tube by the flame of a burner. 2) Place a small quantity of the liquid (0.5 ml) in boiling tube (4-5 mm diameter and mm length). 3) Invert the capillary tube (closed end up ward) and introduce it with its open end; down ward inside the boiling tube (wider tube). 4) Attach the tube to thermometer by rubber band in such a way that the bottom end of the boiling tube is at the middle of the thermometer bulb. 5) Immerse the thermometer in an oil bath and adjust its height through a cork clamp stand assembly. 6) Heat gradually the oil bath by a burner ( or other heating source ); and notice the slow escape of air bubbles from the end of the capillary tube,but near the boiling point of the liquid,a rapid and continuous escape of air bubbles will be observed. 7) Record the reading of the thermometer when the rapid and continuous stream of air bubbles first escape from the capillary tube as boiling point of the liquid. 8) Now remove the heating source from oil bath, the speed at which the escaped bubbles will slacken and finally, when the last bubble makes its appearance and exhibits a tendency to suck back, read thermometer reading immediately, this is the true and accurate boiling point of the liquid because it is the temperature at which the vapor pressure of the liquid is equal to that of atmosphere. 18

20 Melting Point Determination The melting point of crystal solid is the temperature at which the solid begins to change into liquid under atmospheric pressure. For powder substance, the change from the solid to the liquid state is quite sharp (within 0.5 oc).hence the temperature is a valuable mean for identification purposes and an important criterion of purity. Procedure: 1- Close one end of the capillary using the flame of a Benzene burner. 2- Push the closed capillary into the powder sample and inter the powder into the capillary tube and clean the outside of capillary with soft tissue, don't let the powder height exceed (2-3) mm. 3- Attach the capillary tube to the lower end of thermometer in such a way that the substance is at the level of the middle part of the mercury bulb using a rubber band. 4- Insert the attached capillary tube with thermometer to the center of an oil bath. 5- Hang the thermometer by a clamp fixed to stand and adjusts the height properly. Read the changing in temperature. 6- Start the heating operation and slow down before reading the melting point range temperature, at an approximate rate of 2 oc per minute until the compound melts completely. 7- The temperature at which the substance starts to liquefy and the temperature at which the salt has disappeared, the melting point range are observed and recorded. For a pure compound, the melting point range should not exceed (0.5-1) o C, it is usually less. 19

21 Simple Distillation The purpose of this experiment is to separate a volatile liquid from a non- volatile substance or, more usually the separation of two or more liquids of different boiling points. This is usually called fractional distillation. Ideal solution possessing the following properties: 1- There is no heat effect when the components are mixed. 2- There is no change in volume when the solution is formed. 3- The vapor pressure of each component equal to the vapor pressure of the pure substances multiplied by its mole fraction in the solution. 4- There is no chemical reaction between the components in the mixture. Another purpose of such distillation is to purify one substance from impurities. Procedure 1) By using the distillation glass wear. 2) Introduce 100ml of mixture solution required to separate to its components into the round bottomed flask with 2-3 pieces of boiling chips (stone). 3) Fix the thermometer and make sure that the running water is circulating in the condenser. 4) Start the heating process and record the temperature, until mixture start to boil. 5) Adjust the heating rate so that only drops of condensed distillate is collected per minute. 6) Continue recording the temperature, for every 5ml of distillate, until all the mixture has been distilled. 20

22 7) Ensure the separation of two substances when there is a sharp increase of temperature with lower rate of distillation. Esters and Esterification Many of the Esters type RCOOR have pleasant odors, and are produced by the reaction of alcohol and carboxylic acids with the loss of water, according to the following equation The following procedure illustrates the preparation of ethyl acetate ester and its separation from the reaction medium by reacting acetic acid and ethyl alcohol in the presence of conc. H 2 SO 4 : The addition of sulfuric acid increases the rate of reaction towards equilibrium but it doesn't affect the products yield. Procedure: 1- Pipette out 10ml ethyl alcohol to a 250 ml round bottomed flask containing few boiling chips. 2- Add (7.5)ml acetic acid to the alcohol and shake. 3- Add (0.5)ml of concentrated sulphuric acid very slowly, swirling the flask continuously. 4- Heat the mixture to the boiling temperature for 1hr. 21

23 5- Distill-off pure ester form the other contents of the reacting mixture at C maximum temperature. 6- Collect the formed ester and measure of yield in (m1). Preparation of acetic acid Ethanol is a primary alcohol; it contains hydroxyl group which at oxidation give acetaldehyde first and then acetic acid. The oxidative agent (mixture of sodium dichromate and sulfuric acid) is used for the preparation of acetic acid. Aqueous ethanol was added gradually to the hot mixture of aqueous solution of sodium dichromate and sulfuric acid. Procedure 1. Add 10ml of distilled water in around bottom flask, then add 3-5ml of concentrated sulfuric acid with continuous stirring. 2. Add 3-5gm of sodium dichromate to the mixture and shake well to complete dissolving. 3. Put in a separating funnel 1.5ml of alcohol with 6ml of water. 4. Add the mixture in the step (3) to the mixture in the step (2) with stirring during addition (reflux). 5. Heat the mixture by using water bath for 20 minute. 6. Distill the mixture and collect 8ml of the distillate, which is acetic acid. 22

24 7. Make the following tests: a- With litmus paper. b- With sodium hydroxide. c- With ethanol (Note smell ester ethyl acetate). 23