Medical Chemistry Laboratory Manual PDF

AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Experiment name Laboratory Safety Rules Hazard Signs Instrument Analytical Chemistry Experiment No( 4) 11 14 Determination The Concentration Of An Unknown Solution Of Hcl by known Solution Of NaOH Determine The Conce...

AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Experiment name Laboratory Safety Rules Hazard Signs Instrument Analytical Chemistry Experiment No( 4) 11 14 Determination The Concentration Of An Unknown Solution Of Hcl by known Solution Of NaOH Determine The Concentration Of An Unknown Solution Of NaOH by known Solution Of HCL Standardization Of Approximately 0.1 Mol L–1 Sodium Hydroxide Standardization Of Approximately 1 Mol L–1 Hydrochloric Acid Organic chemistry Experiment No( 5) DETERMINATION OF MELTING POINTS Experiment No( 6) DETERMINATION OF BOILING POINTS Experiment (7 ) Recrystallization Of Benzoic Acid Experiment (8) Sublimation process Biochemistry Carbohydrates Tests Experiment (9) 5 Determination Of Solubility Class Indicators Experiment No( 3) 4 13 Titration Experiment No( 2) 3 Solubility Rules Solubility diagram Experiment No( 1) Page no. Molisch Test 18 19 21 22 28 32 35 38 38 42 44 49 51 52 | 1 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Experiment (10) Seliwanoff Test Experiment (11) Bial Test Experiment (12) Fehling's Test Experiment (13) Benedict's test Experiment (14) Barfoed's test Summary of Carbohydrates test Qualitative Tests Of Amino Acids Experiment No.15 Experiment No.16 Experiment No.17 Determination Solubility Of Amino Acid Ninhydrin Test Xanthoproteic Test 54 55 59 61 63 66 69 70 71 74 | 2 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Laboratory safety Rules 1) Contact lenses should not be worn in the lab. 2) Clothing must be secured and shoes must completely cover the foot. 3) A lab coat, gloves should be worn during lab. Experiments. 4) If a chemical should splash in your eyes or on your skin, quickly wash with water for at least 20 minutes. 5) All chemicals in the lab are dangerous because of that do not taste, or smell any chemicals. 6) Never return unused chemicals to their original container. 7) Never work alone in the lab. 8) In the lab area do not touch any equipment, chemicals or other materials . 9) Do not drink or eat food and gum in the lab. 10) Always work in a well-ventilated area. 11) Read carefully instructions of equipment before use. 12) Keep hands from face, eyes, mouth, and body while using chemicals or lab equipment and wash your hands with soap and water after performing all experiments 13) Never remove chemicals or other materials from the lab area. 14) Do not inter hot glassware in cold water. 15) Do not operate a hot plate by yourself and take care that hair, clothing, and hands are a safe distance from the hot plate at all times. 16) Never look into a container that is being heated. | 3 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Flammable substances Explosive substances Toxic substances Harmful substances Oxidizing substances Corrosive substances ‫أكال‬ | 4 AL Ameed University Dentistry Collage Instrument Name 1) Goggles Assist.Lect Ali Naser Medical Chemistry Advantage protects eyes from chemical splashes 2) Bunsen burner 3) Graduated cylinder used to heat substances accurately measures liquid volumes | 5 AL Ameed University Dentistry Collage 4) Spot plate Assist.Lect Ali Naser Medical Chemistry a flat plate with multiple "wells" ‫تستخدم‬ ‫لسحب السائل‬ ‫اصة‬6‫إلى ا‬ 5) Pipet bulb used to pull liquid up into a pipet ‫قضيب‬ ‫التحريك‬ 6) Stirring rod used for stirring ‫لهب‬ 7) Evaporating dish liquids are heated over a flame so that they evaporate, leaving a solid residue ‫رواسب أو‬ ‫راسب‬ | 6 AL Ameed University Dentistry Collage 8) Crucible tongs ‫ملقطات البوتقة‬ 9) watch glass 10) Beaker 11) Thermometer Assist.Lect Ali Naser Medical Chemistry to hold hot crucibles ‫بوتقة‬ to hold solids while being weighed. used to hold liquids measures temperature (Science uses degrees in Celsius) | 7 AL Ameed University Dentistry Collage 12) Balance 13) Volumetric flask ‫دورق الحجم‬ 14) Funnel Assist.Lect Ali Naser Medical Chemistry An Instrument For Determining Weight. for making up solutions to a known volume for pouring liquid or other substance through a small opening 15) Volumetric pipet ‫ماصة‬ measures small amounts of liquids accurately | 8 AL Ameed University Dentistry Collage 16) Wire gauze Assist.Lect Ali Naser Medical Chemistry used to support a container ‫شبكة معدنية‬ 17) Test tube rack holds 5-6 test-tubes in a row ‫شطف‬ 18) Wash bottle used to rinse various pieces of laboratory glassware ‫واني الزجاجية‬3‫ا‬ 19) Test Tube Open Tube Used To Hold Liquid | 9 AL Ameed University Dentistry Collage 20) Hot plate Assist.Lect Ali Naser Medical Chemistry stir plate used to heat and stir substances Means shake and move 21) Filter paper special paper used to separate solids from liquids 22) Erlenmeyer flask used to hold liquids, has narrow neck to prevent splashes | 10 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Definition:Analytical chemistry is the chemistry discipline concerned with the chemical composition of materials. Analytical chemistry also is concerned with developing the tools used to examine chemical compositions. Analytical Chemistry deals with methods for determining the chemical composition of samples of matter. A qualitative method yields information about the identity of atomic or molecular species or the functional groups in the sample; a quantitative method, in contrast, provides numerical information as to the relative amount of one or more of these components. Analytical methods are often classified as being either classical or instrumental. 1) Classical Methods:In the early years of chemistry, most analyses were carried out by separating ‫ترسيب‬ ‫تقطير‬ ‫استخراج‬ components of interest in a sample by precipitation, extraction, or distillation. For ‫كواشف‬ quantitative analyses, the separated components were then treated with reagents that ‫أثمرت‬ yielded products that could be recognized by their colors, boiling points or melting ‫مذيب‬ ‫رائحة‬ ‫بصري‬ points, their solubility in a series of solvents, their odors, their optical activities, or ‫نكسار‬.‫ا‬ ‫مؤشر‬ their refractive indexes. Qualitative Analysis:Qualitative analysis consists of methods for establishing the qualitative chemical composition of a substance—that is, the identification of atoms, ions, and molecules that enter into the composition of the substance being analyzed. The most important characteristics of all methods of qualitative analysis are specificity and sensitivity. | 11 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Specificity characterizes the ability to detect the presence of an unknown element in the presence of other elements—for example, iron in the presence of nickel, manganese, chromium, vanadium, or silicon. Sensitivity is defined as the smallest quantity of an element that can be detected by a given method. Sensitivity of modern methods is expressed in magnitudes of the order of 1 mg (one millionth part of a gram). Quantitative Analysis:Quantitative analysis consists of methods for determining the quantitative composition of materials—that is, the quantitative amounts of the chemical elements ‫مركبات‬ or of certain compounds in the analyzed substance. Along with specificity and sensitivity, the most important characteristic of every method of quantitative analysis is accuracy. Quantitative analyses, the amount of analyte was determined by gravimetric or by titrimetric measurement. ‫ادة التي يجري تحليلها‬1‫ا‬ Gravimetric Methods :– the mass of the analyte or some compound produced from the analyte was determined. Titrimetric Methods:– the volume or mass of a standard reagent required to react completely with the analyte was measured. 2) Instrumental Methods:Measurements of physical properties of analytes, such as conductivity, electrode ‫انبعاث‬ ‫نسبة‬ ‫فلورة‬ potential, light absorption, or emission, mass to charge ratio, and fluorescence, began to be used for quantitative analysis of a variety of inorganic, organic, and biochemical ‫فعال‬ analyte. Highly efficient chromatographic and electrophoretic techniques began to replace distillation, extraction, and precipitation for the separation of components of ‫سابق‬ complex mixtures prior to their qualitative or quantitative determination. These newer methods for separating and determining chemical species are known collectively as instrumental methods of analysis. | 12 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Measurement of physical properties of analytes - such as conductivity, electrode potential, light absorption or emission, mass-to-charge ratio, and fluorescence-began to be employed for quantitative analysis of inorganic, organic, and biochemical analytes. Efficient chromatographic separation techniques are used for the separation of components of complex mixtures. Solubility rules dictate whether a compound will dissolve in water. Therefore, solubility rules can help you determine what state the products of a chemical reaction will have. When you write out a chemical equation, you can use solubility rules to label the predicted states of the compounds involved. This is especially useful when monitoring a solution for precipitates. dictate whether a compound will dissolve in water. Therefore, solubility rules can help you determine what state the products of a chemical reaction will have. When you write out a chemical equation, you can use solubility rules to label the predicted states of the compounds involved. This is especially useful when monitoring a solution for precipitates. Soluble Compounds:All nitrates are soluble in water. Therefore, any compound containing the nitrate ion, NO3-, will dissolve in water. Most chlorides, or compounds containing Clions, are soluble in water. Most sulfates, or compounds containing SO4 2- ions, are also soluble in water. Finally, all ionic compounds containing group IA metals or ammonium ions are soluble. For example, NH4OH will dissolve into NH4+ and OHions in solution. | 13 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Exceptions to Soluble Compounds:Chlorides containing copper (I), mercury(II) or silver ions will not dissolve. Lead(II) chloride is slightly soluble, but will form as a precipitate in many reactions. Sulfates containing strontium, barium and lead(II) are insoluble. Sulfates containing calcium and silver are slightly soluble. Like lead(II) chloride, calcium sulfate and silver sulfate will precipitate in many reactions. Solubility class determination is useful for knowing the type of the functional group, the polarity of the compound, the molecular weight and acidity degree. Solvents that are used in determination of the solubility class are: 1- Water 2- Ether 3- 5% NaOH 4- 5% NaHCO3 5- 5% HCl 6- conc.H2SO4 The amounts of material to use for a solubility test are somewhat flexible. Use 23 drops of a liquid or approximately 10 mg of a solid. Unless the solid is already a fine powder, crush a small amount of the solid on a watch glass with the back of a spatula. Do not weigh the solid; simply use enough to cover the tip of a small spatula. Your instructor will demonstrate how to estimate the correct amount. Place the appropriate amount of either your solid or liquid unknown in a small test tube and proceed with the following solubility tests. | 14 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry 1)water solubility:Add approximately 6 drops of water to the test tube containing your unknown. Shake the tube and/or stir with a glass stirring rod. A soluble unknown will form a homogeneous solution with water, while an insoluble liquid will remain as a separate phase. A liquid which is soluble in water may be either a low molecular weight polar compound of up to 5 carbon atoms or less. You may add additional water, up to 1 mL, if your compound does not completely dissolve with the smaller amount. Check the pH of the water to determine if your unknown is partially or completely soluble in water and whether your compound has changed the pH of the water.  pH paper turns red: water soluble acidic compound  pH paper turns blue: water soluble basic compound  pH paper does not change color: water soluble neutral compound or insoluble compound An organic compound which is soluble in water is typically a low molecular weight polar compound of up to 5-6 carbon atoms or less. 2) Ether :Ether is non-polar solvent with dielectric constant of 4.3. It cannot form hydrogen bonding; therefore it differs from water in that it cannot dissolve the ionic compounds such as salts. Ether dissolves most water insoluble compounds therefore in determining the solubility class it is important only with water insoluble compounds. Accordingly two probabilities are there: | 15 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry 1. Compounds that is soluble in both water and ether and such compounds:  Are non-ionic.  Contain 5 or less carbon atoms.  Contain an active group that is polar and can form hydrogen bonding  Contain only one strong polar group. This division of compounds is given S1class and includes e.g. aldehydes, ketones and Aliphatic acids. 2. Compounds that are soluble in water but not in ether and such compounds :  Are ionic.  Contain one or more polar groups with no more than 4 carbon atoms per each polar group. This group is classified as S2class. Examples of this group are: a. High molecular weight compound such as halogen derivatives. b. Ionic salts such as salts of carboxylic acids and amines. c. Compounds with more than one active group such as poly hydroxylated compounds and carbohydrates. Note that solubility in ether is tested only for water soluble compounds. For water insoluble compounds use the left side of solubility classification scheme, i.e. test solubility in sodium hydroxide rather than ether. 3)5%NaOH Solubility :Add approximately 1 mL of 5% NaOH in small portions of about 6 drops each to the test tube containing your unknown. Shake test tube vigorously after the addition of each portion of solvent. Solubility will be indicated by the formation of a homogeneous solution, a color change, or the evolution of gas or heat. If soluble, then your unknown is behaving as an organic acid. The most common organic acids are | 16 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry carboxylic acids and phenols. Carboxylic acids are usually considered stronger acids than phenols, but both of these acids will react with NaOH (a strong base). 4)5%NaHCO3 Solubility:Add approximately 1 mL of 5% NaHCO3 in small portions of about 6 drops each to the test tube containing your unknown. Shake test tube vigorously after the addition of each portion of solvent. Solubility will be indicated by the formation of a homogeneous solution, a color change, or the evolution of gas or heat. If soluble, then it is a strong organic acid. If not, then it is a weak organic acid, if it dissolves in NaOH. The most common weak organic acid are phenols. Typically, only a carboxylic acid will react with NaHCO3. 5)5%HCl Solubility:Add approximately 1 mL of 5% HCl; in small portions of about 6 drops each to the test tube containing your unknown. Shake test tube vigorously after the addition of each portion of solvent. Solubility will be indicated by the formation of a homogeneous solution, a color change, or the evolution of gas or heat. If your compound is HCl-soluble, then it is an organic base. Amines are the most common organic base. If insoluble in all solutions, then your unknown is not an acidic or basic organic compound. 6) Conc. H2SO4 If the compound is insoluble in water, sodium hydroxide and hydrochloric acid, test its solubility in concentrated sulfuric acid. If the compound is soluble in H2SO4, it belongs to class N which include neutral compounds as alcohol, aldehyde, ketones, esters, ethers (of high molecular weight) and unsaturated hydrocarbons. In other hand compounds that insoluble to class I which includes inert aliphatic hydrocarbons. | 17 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Below is a very useful scheme for solubility classification: | 18 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Titration Titration is an analytical technique which allows the quantitative determination of a specific substance (analyte) dissolved in a sample. It is based on a complete chemical reaction between the analyte and a reagent (titrant) of known concentration which is added to the sample. A well-known example is the titration of acetic acid (CH3COOH) in vinegar with sodium hydroxide, NaOH: CH 3COOH +NaOH → CH3COO- + Na+ +H2O Analyte Reagent Reaction Products The titrant is added until the reaction is complete. In order to be suitable for a determination the end of the titration reaction has to be easily observable. This means that the reaction has to be monitored (indicated) by appropriate techniques, e.g. potentiometry (potential measurement with a sensor) or with colour indicators. The measurement of the dispensed titrant volume allows the calculation of the analyte content based on the stoichiometry of the chemical reaction. The reaction involved in a titration must be fast, complete, unambiguous and observable. Advantages Of Titration :There are several reasons why titration is used in laboratories worldwide: • Titration is an established analytical technique. • It is fast. • It is a very accurate and precise technique. • A high degree of automation can be implemented. • Titration offers a good price/performance ratio compared to more sophisticated techniques. | 19 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry • It can be used by low-skilled and low-trained operators. • No need for highly specialized chemical knowledge. Types of Titrations: 1. Strong Acid / Strong Base pH at equivalence point = 7 2. Weak Acid / Strong Base pH at equivalence point >7 3. Strong Acid / Weak Base pH at equivalence point <7 *Note: weak acid / weak base titrations are too complicated and are almost never carried out. Chemical Analysis Qualitative And Quantitative Analysis:There are two types of chemical analysis: qualitative and quantitative. Qualitative analysis is the process of identifying what is in a chemical sample whereas quantitative analysis is the process of measuring how much is in the sample. In this section we are concerned with methods of quantitative analysis. Volumetric Analysis:In practical terms, volumetric analysis is achieved by a titration procedure. In ‫سحاحة‬ ‫ماصة‬ a titration, one of the solutions is added from a burette to a pipetted volume of the other solution in a conical flask. The point at which the reaction between the two is just complete is usually detected by adding a suitable indicator to the solution in the flask. It is customary, although not essential, to have the solution of known concentration in the burette. ‫ أن يكون لديك محلول التركيز‬،‫ على الرغم من أنه ليس ضروريا‬،‫عتاد‬B‫من ا‬ .‫عروف في السحاح‬B‫ا‬ | 20 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry There are numerous types of titration but the most common are: ‫تفاع)ت متعادلة‬  acid-base titrations, which are based on neutralization reactions ‫كسدة والتخفيض‬-‫ت ا‬/‫والتي تعتمد على تفاع‬  redox titrations, which are based on oxidation–reduction reactions  complexometric titrations, which are based on complex-formation reactions. Standard Solutions:As mentioned above, a standard solution is one of accurately known concentration and it can be prepared directly from a solute if that solute is a primary standard. To be suitable as a primary standard, a substance must meet a number of requirements.  It must have a high purity.  It must be stable in air and in solution. ‫يجب أن تكون قابلة للذوبان بسهولة في مذيب‬  It must be readily soluble in a solvent (normally water) . ‫تخفض‬  It should have a reasonably large relative formula mass in order to minimize the uncertainty in the mass of substance weighed out. Indicators Indicators are compounds that allow us to detect the end-points of titrations. ‫عادة ما يخضعون لتغيير مفاجئ في اللون‬ Typically they undergo an abrupt color change when the titration is just complete. In general, an indicator reacts in a similar manner to the substance being titrated and so indicator choice will depend on the titration type: acid – base, redox or complexometric.  An acid–base indicator is normally a weak organic acid that will dissociate in aqueous solution, establishing the following equilibrium: ‫عادة ما يكون مؤشر الحمض القاعدي حمضا عضويا ضعيفا ينفصل في‬ :‫ يحدد التوازن التالي‬،‫محلول مائي‬ HIn(aq) + H2O(l) H3O+(aq) + In (aq) | 21 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry ancient Hebrew unit of liquid capacity equal to about 1.5 gallon (5.7 liters) Indicator HIn colour pH range of colour In colour change Bromophenol blue Yellow 3.0–4.6 Blue Methyl red Red 4.2–6.3 Yellow Bromothymol blue Yellow 6.0–7.6 Blue Phenol red Yellow 6.8–8.4 Red Phenolphthalein Colourless 8.3–10.0 Pink Experiment No (1) Determination the Concentration of an Unknown Solution of Hcl by known Solution of NaOH Purpose: To determine the concentration of an unknown solution of HCl by titrating with a 0.1 mol/L solution of NaOH. Introduction:  Neutralization reactions involve the reaction of an acid and a base to produce a salt (ionic compound) and water. Acid + Base Salt + Water Example: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) (Net Equation: H+(aq) + OH-(aq) H2O(l)) | 22 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry  Titration is a process of neutralization  Titration is commonly used to determine the concentration of an acid or base in a solution.  This process involves a solution of known concentration (the titrant or standard solution) delivered from a burette into the unknown solution (the analyte) until the substance being analyzed is just consumed.  The moles of H+ = moles of OH- at this point (called the equivalence point).  Information about the analyte (i.e. concentration) can be calculated at the equivalence point.  The volume of titrant is recorded and the moles of titrant can then be calculated using n = C*V Where n = no. of moles, C = concentration in mol/L V = volume in L. The moles of titrant can then be used to calculate the moles of analyte consumed, and thus its concentration as well.  The end point in a titration is often signaled by the color change of an indicator and occurs just slightly past the equivalence point.  An indicator is a substance (weak acid) that has distinctively different colors in acidic and basic media. | 23 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry *Not all indicators change color at the same pH, so the choice of indicator for a particular titration depends on the strength of the acid and base. An indicator is chosen whose end point range lies on the steep part of the titration curve.  The progress of an acid-base titration is often monitored by plotting the pH of the solution being analyzed as a function of the amount of titrant added (called a titration curve). Materials:Standardized NaOH solution (0.1 mol/L)* Unknown HCl solution** Phenolphthalein indicator solution 2-50 mL Burets 250 mL Erlenmeyer flask Distilled water 25 mL graduated cylinder Digital pH meter *Prepare the NaOH solution accurately using a volumetric flask. **For best results, use between 0.8 and 1.2 mol/L; prepare accurately using a volumetric flask. Procedure: 1. Rinse* and fill a burette with standardized 0.1 mol/L NaOH. ‫محبس‬ For short time Open the stopcock briefly to allow any air bubbles to pass through. Record the initial volume of NaOH in the burette to the nearest 0.05 mL. | 24 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry 2. Add 10.00 mL of unknown HCl solution (delivered from the Burette) into an 250 mL Erlenmeyer flask. Add 2 drops of phenolphthalein indicator. Then add 25 mL of distilled water to this solution 3. Gradually dispense some of the NaOH solution drop-by-drop from the burette into the solution in the Erlenmeyer flask. Swirl the flask constantly as the drops are added. Note any color changes observed, and do so constantly as NaOH is added to the HCl solution. 4. As the equivalence point is approached, a pinkish color will appear. 5. Record the volume of NaOH required to reach the endpoint of the titration. 6. Repeat the titration until 3 accurate trials have been completed. The volumes of NaOH required to reach the endpoint should agree within +/- 0.1 ml. 7. Prepare a data table of your results, including the initial, final and total volumes of NaOH required for each titration. 8. Plot the pH as a function of the volume of NaOH added for one good trial. 9. calculate the concentration of the unknown HCl solution. Use either the volume of NaOH from your best trial, or average the three best trials and use this average volume of NaOH. | 25 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Calculations:Trial 1 Initial vol. Final vol. Total vol. Burette Reading Trial 2 Initial vol. Final vol. Total vol. Burette Reading Trial 3 Initial vol. Final vol. Total vol. Burette Reading Trial 1+Trial 2+Trial 3 Average vol. = = 3 From Burette M1* V1 (acid) =M2 *V2 (base) Summary: Titration is a process of neutralization whereby a titrant (a solution of known concentration) is delivered into an unknown solution (the analyte) until the unknown solution is completely neutralized. This allows information about the unknown solution to be determined. An indicator is a weak acid that is placed into the unknown solution to determine the endpoint of the titration (the pH at which the indicator changes color). The equivalence point of the titration is the point when the moles of | 26 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry H+ are equal to the moles of OH- in a titration. A titration curve is a plot of pH as a function of the volume of titrant added. WRITE YOUR NOTES:- | 27 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Experiment No (2): Determine the Concentration of Unknown Solution of NaOH by known Solution Of HCL To determine the concentration of an unknown solution of NaOH by titrating with a 0.1 mol/L solution of HCL. Introduction Titration is a process in which the concentration of a solution is determined by measuring the volume of that solution needed to react completely with a standard solution of known volume and concentration. The process consists of the gradual addition of the standards solution to a measured quantity of the solution of unknown concentration until the number of moles of hydronium ion, H3O+, equals the number of moles of hydroxide ion, OH-, The point at which equal numbers of moles of acid and base are present is known as the equivalence point. An indicator is used to signal when the equivalence point is reached. The chosen indicator must chance color very near or at the equivalence point. The point at which an indicator changes color is called the end point of the titration. Phenolphthalein is an appropriate choice for this titration. In acidic solution, phenolphthalein is colorless, and in basic solution, it is pink. In this experiment, you will be given a standard HCl solution and told what its concentration is. You will carefully measure a volume of it and determine how much of the NaOH solution of unknown molarity is needed to neutralize the acid sample. Using the data you obtain you can calculate the molarity of the NaOH solution. | 28 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Materials  0.106M HCl (Acid)  NaOH solution of unknown molarity (base)  Phenolphthalein indicator  Two 50-mL burets  One small beaker -to fill burets  One Erlenmeyer flask-to collect solutions  One small funnel  Double burette clamp Procedure:1. With the stopcock closed, fill the burette with unknown NaOH solution to the top (close to the zero mark, it does not have to be exact). Remove any bubbles trapped in the stopcock or in the tip of the burette . 2. In your data table, record the initial reading of each burette, estimating to the nearest 0.05mL. For consistent results, have your eyes level with the top of the liquid each time you read the burette. Always read the scale at the bottom of the meniscus. The burette measures volume dispensed, NOT volume contained. 3. Place Erlenmeyer flask under acid burette. Dispense 8-10 mL of HCl from the burette into the Erlenmeyer flask. 4. Add 2 drops of phenolphthalein solution as an indicator to the Erlenmeyer flask. (The solution should remain clear) 5. Now, slowly add NaOH solution from the “base” burette to the flask with the 0.106 M HCl in it. As you add the base, gently swirl the solution in the flask. | 29 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry 6. A pink color will appear and quickly disappear as the solutions are mixed. As more and more base is added, the pink color will persist for a longer time before disappearing. This is a sign that you are nearing the end point. Continue to add sodium hydroxide more slowly, until a single drop of base turns the solution a pale pink color that persists for 15–30 seconds. 7. When you are sure that you have achieved the end point, record the final volume reading of each burette. 8. Discard the neutral solution down the drain, rinse the flask with water, and repeat steps for a second trial. Try to use the same amount of acid as you did in trial 1. Do not refill the burettes; use the final volume reading of the last trial as the initial volume reading for the second trial. Conduct a third trial if time and solutions still remain. Calculations:Trial 1 Initial vol. Final vol. Total vol. Burette Reading Trial 2 Initial vol. Final vol. Total vol. Burette Reading Trial 3 Initial vol. Final vol. Total vol. Burette Reading | 30 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Trial 1+Trial 2+Trial 3 Average vol. = = 3 From Burette M1* V1 (acid) =M2 *V2 (base) WRITE YOUR NOTES:- | 31 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Experiment No (3): Standardization Of Approximately 0.1 Mol L–1 Sodium hydroxide Introduction Sodium hydroxide is not a primary standard and so a standard solution of it cannot be prepared directly from the solid. However, a solution of approximate concentration can be prepared and its exact concentration determined by titrating it against an acid of accurately known concentration using a suitable indicator. In this experiment, a sodium hydroxide solution is standardized against the 0.1 mol l –1 oxalic acid solution prepared in Experiment 1A. The stoichiometric equation for the titration reaction is: (COOH)2 + 2NaOH → 2H2O + (COONa)2 Requirements  50 cm3 burette standardized oxalic acid solution (approx. 0.1 mol l–1)  10 cm3 pipette sodium hydroxide solution (approx. 0.1 mol l–1)  100 cm3 beakers phenolphthalein indicator  100 cm3 conical flasks deionized water  Wash bottle Hazcon Wear eye protection and if any chemical splashes on the skin, wash it off immediately. 0.1 mol l–1 oxalic acid irritates the eyes and skin. 0.1 mol l–1 sodium hydroxide is corrosive to the eyes and skin. Phenolphthalein indicator solution is highly flammable and irritating to the eyes because of its ethanol content. | 32 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Procedure 1. Rinse the 10 cm3 pipette with a little of the oxalic acid solution and pipette 10 cm3 of it into a conical flask. 2. Add two or three drops of phenolphthalein indicator to the oxalic acid solution in the flask. 3. Rinse the 50 cm3 burette, including the tip, with the sodium hydroxide solution and fill it with the same solution. 4. Titrate the oxalic acid solution with the sodium hydroxide solution from the burette until the end-point is reached. This is indicated by the appearance of a pink colour. 5. Repeat the titrations until two concordant results are obtained. 6. Calculate the concentration of the sodium hydroxide solution. Calculations:Trial 1 Initial vol. Final vol. Total vol. Burette Reading Trial 2 Initial vol. Final vol. Total vol. Burette Reading Trial 3 Initial vol. Final vol. Total vol. Burette Reading | 33 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Trial 1+Trial 2+Trial 3 Average vol. = = 3 M1* V1 (acid) =M2 *V2 (base) WRITE YOUR NOTES:- | 34 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Experiment No (4): Standardization of Approximately 1 Mol L–1 Hydrochloric Acid Introduction Hydrochloric acid is not a primary standard and so a standard solution of it cannot be prepared directly. However, a solution of approximate concentration can be prepared and its exact concentration determined by titrating it against a base of accurately known concentration using a suitable indicator. In this experiment, approximately 1 mol l–1 hydrochloric acid is first diluted and then standardized against the 0.1 mol l–1 sodium carbonate solution prepared in Experiment 2A. The stoichiometric equation for the titration reaction is: Na2CO3 + 2HCl → H2O + CO2 + 2NaCl Requirements  50 cm3 burette standardized sodium carbonate solution  10 cm3 and 25 cm3 pipettes (approx. 0.1 mol l–1)  100 cm3 beakers hydrochloric acid (approx. 1 mol l–1)  250 cm3 standard flask screened methyl orange indicator  100 cm3 conical flasks (or any other suitable indicator)  Wash bottle deionized water Hazcon Wear eye protection and if any chemical splashes on the skin, wash it off immediately. 1 mol l–1 hydrochloric acid irritates the eyes and skin. | 35 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Procedure 1. Rinse the 25 cm3 pipette with a little of the 1 mol l–1 hydrochloric acid solution. 2. Dilute the sample of hydrochloric acid by pipetting 25 cm3 of it into a clean 250 cm3 standard flask and making it up to the graduation mark with deionized water. *Stopper the standard flask and invert it several times to ensure the contents are thoroughly mixed. 3. Rinse the 10 cm3 pipette with a little of the sodium carbonate solution and pipette 10 cm3 of it into a conical flask. 4. Add two or three drops of screened methyl orange indicator to the sodium carbonate solution in the flask. 5. Rinse the 50 cm3 burette, including the tip, with the diluted hydrochloric acid and fill it with the same solution. 6. Titrate the sodium carbonate solution with the diluted hydrochloric acid from the burette until the end-point is reached. This is indicated by a green to mauve colour change. 7. Repeat the titrations until two concordant results are obtained. 8. Calculate the concentration of the diluted hydrochloric acid and hence the undiluted hydrochloric acid. | 36 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Calculations:Trial 1 Initial vol. Final vol. Total vol. Burette Reading Trial 2 Initial vol. Final vol. Total vol. Burette Reading Trial 3 Initial vol. Final vol. Total vol. Burette Reading Trial 1+Trial 2+Trial 3 Average vol. = = 3 M1* V1 (acid) =M2 *V2 (base) WRITE YOUR NOTES:- | 37 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Organic chemistry Experiment No. (5): Determination Of Melting Points Introduction: The melting point of a compound is the temperature at which it changes from a solid to a liquid. This is a physical property often used to identify compounds or to check the purity of the compound. It is difficult, though, to find a melting point. Usually, chemists can only obtain a melting range of 2 – 3 oC accuracy. This is usually sufficient for most uses of the melting point. A pure, nonionic, crystalline organic compound usually has a sharp and characteristic melting point (usually 0.5-1.0 oC range). A mixture of very small amounts of miscible impurities will produce a depression of the melting point and an increase in the melting point range. Consequently, the melting point of a compound is a criterion for purity as well as for identification. The melting point of an organic solid can be determined by introducing a tiny amount into a small capillary tube, attaching this to the stem of a thermometer centered in a heating bath, heating the bath slowly, and observing the temperatures at which melting begins and is complete. Pure samples usually have sharp melting points, for example 149.5-150 oC or 189-190 oC; impure samples of the same compounds melt at lower temperatures and over a wider range, for example 145-148 Co or 186-189 Co. | 38 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Purpose: The purpose of this experiment is to determine the melting points of various organic compounds and to use these to identify unknowns. Equipment / Materials:  Mel - Temp apparatus  capillary tubes  Thermometer solid  organic compounds  mortar and pestle (optional)  dropping tubes Safety:  Always wear safety glasses in the lab.  The parts on the top of the Mel - temp are HOT while it is turned on. Do not touch these parts or place your eye on the eyepiece, you will get burned.  Capillary tubes break very easily, handle them with caution. Procedure: 1. Obtain a capillary melting point tube and a known compound. 2. Place a small amount of the compound on a clean surface. Push the open end of the tube into the compound. Some of the sample will now be in the top of the tube. 3. Hold the closed end of the capillary tube over a dropping tube; the dropping tube should be held perpendicular to the table and a couple of inches above the table surface. Drop the capillary tube into the dropping tube; the capillary tube will bounce on the table packing the powder into the bottom. | 39 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry 4. Place the capillary melting point tube in the Mel-temp apparatus chamber. Start with a setting of two to two and a half; the temperature should slowly rise. The sample should be observed continuously, so that the melting point of the sample is not missed. 5. Heat slowly to acquire the most accurate results. Record the melting range, which begins when the sample first starts to melt and ends when the sample is completely melted. 6. Allow the Mel-Temp to cool. Obtain an unknown sample and determine its melting range. Identify the unknown by comparing the data of the knowns the class has obtained. 7. Time permitting, pulverize a mixture of two known substances used for practice with a mortar and pestle and determine the melting point of the mixture. | 40 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Data Table: compound melting range - oC compound melting range - oC compound melting range - oC WRITE YOUR NOTES:- | 41 AL Ameed University Dentistry Collage Experiment No. (6): Assist.Lect Ali Naser Medical Chemistry Determination Of Boiling Points Introduction: The boiling point of a compound is the temperature at which it changes from a liquid to a gas. This is a physical property often used to identify substances or to check the purity of the compound. It is difficult, though, to find a boiling point. Usually, chemists can only obtain a boiling range of 2 – 3 oC accuracy. This is usually sufficient for most uses of the boiling point. Purpose: The purpose of this experiment is to determine the boiling points of various organic compounds and to use these to identify unknowns. Equipment / Materials:  closed end capillary tube  hot plate  liquid organic compounds  thermometer  small test tube  250 mL beaker Safety:  Always wear safety glasses in the lab.  Capillary tubes break very easily, handle them with caution.  Be careful with the thermometer | 42 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Procedure: 1. Place a few milliliters of a known liquid organic compound in a small test tube. 2. Place the capillary tube into the test tube with the closed end upward. 3. Clamp the test tube to a ring stand, and immerse a thermometer in the test tube. 4. Fill a 250 mL beaker 3/4 full with water, and place on the hot plate. Carefully lower the test tube and thermometer combination into the beaker of water so that the test tube is immersed half way in the water. 5. Begin to heat the hot plate/water slowly. As the liquid approaches its boiling point, a few bubbles will be observed flowing out of the end of the capillary tube. When a steady stream of bubbles are observed, turn off the hot plate and allow the contents of the test tube to cool. 6. As the contents of the test tube cools, observe the capillary tube carefully. When the liquid begins to flow into the capillary tube, record the temperature of the liquid as its boiling point temperature. Substance acetone methanol Boiling point (oC) 56-57 65 ethanol 78-79 propanol 97-98 2-propanol 82-83 | 43 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Data Table: Compound Boiling Range - Compound Boiling Range - WRITE YOUR NOTES:- Experiment No. (7) : Recrystallization of Benzoic Acid Purpose: To purify samples of organic compounds that are solids at room temperature. Recrystallization is a method of purifying a solid. There are two types of impurities: those more soluble in a given solvent than the main component and those less soluble. (If there are any impurities that have the same solubility as the main component, then a different solvent needs to be chosen.) When organic substances are synthesized in the laboratory or isolated from plants, they will obviously contain impurities. Several techniques for purifying these compounds have been developed. | 44 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry The most basic of these techniques for the purification of organic solids is recrystallization, which relies on the different solubilities of solutes in a solvent. Compounds, which are less soluble, will crystallize first. The crystallization process itself helps in the purification because as the crystals form, they select the correct molecules, which fit into the crystal lattice and ignore the wrong molecules. This is of course not a perfect process, but it does increase the purity of the final product. A suitable recrystallization solvent should also be partially volatile in order to be easily removed from the purified crystals. The solvent should not react with the compound being purified and it should have the boiling point below the melting point of the compound being purified because solid melts before dissolves (oiling out). In selecting a good recrystallization solvent one should also consider flammability, toxicity, and expense. In selecting a solvent consider that like likes like. Polar compounds dissolve polar compounds and non-polar compounds dissolve nonpolar compounds. The most commonly used recrystallization solvents are presented in the following table. | 45 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Equipment / Materials: Hot plate 125-mL Erlenmeyer flask ice spatula Büchner funnel 50 mL beaker weighing paper Stirring rod filter paper impure benzoic acid 25 mL graduated cylinder benzoic acid boiling stones (chips) Procedures:Using a weighing paper, weigh out about 1.00 g of “impure Benzoic acid for recrystallization” and transfer it to a 125-ml Erlenmeyer flask. Add about 20 ml distilled water, using a graduated cylinder, to the flask and bring the mixture to the boiling point by heating on a hot plate, while stirring the mixture and boiling gently to dissolve benzoic acid completely. (Fig 1) Remove the flask from the hot plate and examine the solution. If there are particles of benzoic acid still undissolved, then add an additional amount of hot or cold water in small increments and resume heating the solution. The objective is to dissolve the entire solid in only as much as hot or near boiling solvent (water) as is necessary. | 46 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Do not add too much water or the solution will not be saturated and the yield of purified benzoic acid will be reduced. Keep adding water in small amounts (several drops at a time from a Pasteur pipette) until all of the benzoic acid is dissolved and the solution is boiling. If the solution is completely clear (though not necessarily colorless) and no solid benzoic acid is visible, then add additional 10-15 ml water to the mixture and place the Erlenmeyer flask on a countertop where it will not be disturbed and cover with an upside-down small beaker (to prevent dust contamination). Allowing the flask to cool slowly will give the best-shaped crystals after about 5-10 minutes. If crystallization does not occur after 10 minutes, scrape the sides of the flask above the level of the solution with the sharp end of a glass rod hard enough to audibly scratch the interior surface of the flask. This may dislodge some undetectable, small crystals that will drop into the solution and "seed" the solution, helping to induce crystallization. A seed crystal can serve as a nucleation point for the crystallization process. Cooling the solution in an ice bath may also help at this point. When the crystals have formed completely (may require ice bath), collect your solid chemical by setting up a vacuum (suction) filtration on a properly fitted filter paper in a clean Büchner funnel apparatus as described by your instructor. (Fig 2) | 47 AL Ameed University Dentistry Collage Assist.Lect Ali Naser Medical Chemistry Calculate the percent recovered using the following written formula and determine the melting point of your recrystallized benzoic acid. Weight of benzoic acid obtained after recrystallization % Recovered = x100 Weight of benzoic acid before recrystallization WRITE YOUR NOTES | 48