Istanbul Medipol University Analytical Chemistry Practice I PDF

İSTANBUL MEDİPOL UNIVERSITY SCHOOL OF PHARMACY ANALYTICAL CHEMISTRY DEPARTMENT ANALYTICAL CHEMISTRY PRACTICE I EXPERIMENT I: HCl GROUP CATIONS (CATION I) Student Name-Surname Student Number Bench Number...

İSTANBUL MEDİPOL UNIVERSITY SCHOOL OF PHARMACY ANALYTICAL CHEMISTRY DEPARTMENT ANALYTICAL CHEMISTRY PRACTICE I EXPERIMENT I: HCl GROUP CATIONS (CATION I) Student Name-Surname Student Number Bench Number Date of Experiment Results of Experiment Quiz Grade: Experiment Grade: Student’s Signature Signature (This part will be signed by the Res. Assist.) Fall Semester 2024-2025  ANALYTICAL CHEMISTRY PRACTISE SAFETY AND LABORATORY RULES 1. Be quiet in the laboratory and corridors of the entrance to the laboratory. 2. It is forbidden to work alone in laboratories. 3. It is strictly forbidden to eat or drink anything in laboratories. 4. Students coming without a lab coat, disposable gloves, goggles, and cleaning cloth will not be admitted to the laboratory. 5. During the experiment, a laboratory coat should be worn, and the front of the lab coat should be buttoned. 6. Students with long hair should tie their hair from the back. Students who use scarves should have the ends of their scarves inside their lab coats. Long dangling jewelry should not be worn. 7. Shoes that protect the feet should be worn against any chemical spillage hazard in the laboratory. Open fronts (sandals, slippers, etc.) or heeled shoes should not be worn. 8. Attention should be paid to the location of safety-related materials and how to use them. 9. During the experiment, it is forbidden to text, talk, take pictures, etc. on the phone. Do not enter the laboratory with phones/bags. 10. Chemicals with gas and vapor output (concentrated acid, etc.) should be worked on the fume hood. The lids of the chemicals and solvents used should not be left open. These chemicals should be used quickly and then the lids should be closed immediately. 11. Flammable liquids should not be used near the Bunsen burner. 12. When using a pipette, it is forbidden to withdraw the solvent with the mouth. Rubber bulb must be used when transferring liquids from one container to another container with a pipette. 13. Bench (work area) and sinks should be used/left clean. Chemical waste should be poured into the collection container on which explanatory information is located. 14. When receiving/weighing solids, they should not be poured on the bench and should not be left open. The spatula used when receiving/weighing solids should be left in a clean place. 15. Pipettes should not be immersed in glass bottles. A small beaker should be taken and used as such. 16. Inform the laboratory supervisor about any accidents and pollution. Acid and base accidents: An acid or base accident should be reported immediately to the laboratory supervisor. The area exposed to acid or base should be urgently washed with plenty of water. In the case of cuts that occur during the experiment: The cut area should not be washed with water. After some blood flow, a tampon should be made to the cut place and the health institution should be visited. 17. Before starting the experimental studies in the laboratory, it is necessary to have information about the theoretical issues related to the experiments to be carried out, the devices to be established, the chemical substances (lab manual, textbook, etc.). 18. The student working in the laboratory should keep the consumables (pliers, spatula, sample container, funnel, etc.), gloves, cleaning cloth, protective glasses, laboratory sheet delivered to him for laboratory work in the study area during the experiment. 19. Experiments that are not responsible should not be carried out. Devices and materials related to someone else's work should not be touched. 20. Each student must study individually in the place determined for him. 21. It is forbidden to walk between the benches in the laboratory and to leave the laboratory without permission. 22. Distilled water bottles should be filled from the distilled water canisters located at the head of each bench. The taps of distilled water canisters should not leave unnecessarily open. 23. Tap water should be used first when cleaning glass materials. Then it should be cleaned with distilled water in the distilled water bottle. Distilled water canister/faucet should not be used directly for cleaning. 24. Distilled water bottles should be left in place and full after the laboratory work is finished. 25. It should not be gathered around water baths and centrifuge devices. 26. The work area in the laboratory should not be abandoned dirty and messy. When leaving the laboratory, each student must show the weekly selected "Bench Responsible" of the bench where he/she works. The "Bench Responsible" selected on a weekly basis is responsible for the clean use of the entire bench. 27. When a question is to be asked, the instructor/laboratory supervisor should be waited by raising hand at the workplace without calling out loudly. 28. After the first one and a half (1:30) hour is completed people who have completed their experiment can start to give results. 29. The results of each experiment performed in the laboratory will be evaluated over a hundred (100) full points. If you find two (2) unknown samples given to you for the qualitative analysis part, one hundred (100), if you find one correct the grade will be seventy (70), and if you cannot find both, your weekly experiment grade will be evaluated as forty (40). For the quantitative analysis part, the results given will be scored according to their proximity to the correct result. If a result is far from the correct result, the grade of the relevant experiment will be evaluated as forty (40). You are allowed to give only one result for each experiment. 30. Those who do not participate in the experiment during the experiment week must come to the laboratory during the make-up week and complete the relevant experiments. CHAPTER 1. LABORATORY TECHNIQUES AND SAFETY Safety is the most important issue in the laboratory. It is possible to prevent most of the accidents that may be encountered in a laboratory by taking only simple precautions. For this, it is necessary to know the materials to be used well and to have a good grasp of the important points required for a safe laboratory practice. 1.1. Laboratory Rules and Practical Information As long as the rules are followed, the laboratory is not a dangerous place to be feared. First of all, it should be kept in mind that the laboratory is a place where serious work is done, white laboratory coats should be worn, hair should not be messy/dangling scarf edges should not be outside the lab coat. In particular, the eyes should be protected from the effects of chemical substances and protective glasses should be used during the experiments. It is inconvenient to use contact lenses in the laboratory, chemical vapors can leak between the eye and the contact lens, leading to harmful formations that show their effect slowly. During the use of chemicals and solutions, great care should be taken not to get on the hands, face and body. In case of any contamination, it can be intervened in the laboratory at the first aid level. However, in severe cases, the hospital should be consulted. You must never taste, handle them with bare hands, eat and drink, and smell chemicals and solutions in the laboratory directly by bringing the nose closer. If odor identification is required, it should be done by approaching the distance where the smell of some vapor sent to the nose is felt by manually fanning over the container. Care should be taken to ensure that the tools and glass materials to be used in the experiment are clean, and broken and cracked tools should not be worked with. At the end of the experiment, the workplace and the materials used should be cleaned. When acid or any other corrosive chemical is spilled anywhere, it should be washed off immediately with plenty of water. When washing glassware in the analytical chemistry laboratory, it should first be washed and rinsed with detergent and tap water, and then rinsed again with distilled water. Distilled water must be used to dilute and top off the solutions used in the laboratory. When buying chemicals, the label on the container should be read carefully and it should be ensured that the correct substance is taken. In addition, the chemicals used should not be taken directly from large bottles. As much as required, liquid reagents should be placed in reagent bottles and solids should be placed in wide-mouth glass or plastic bottles or jars with lids. Reagent bottles should be labeled with the name and concentration of the reagent and their lids should not be left open during use, but tightly closed. Glass bottles with glass lids should be used for reagents such as HNO3 (nitric acid or nitrate acid), HClO4 (perchloric acid) that affect organic substances. HF (hydrofluoric acid or fluorine acid) and concentrated alkaline hydroxide solutions that affect glass should be stored in plastic bottles. When taking a chemical or solution from the container in which it is located, the material used must be dry and clean. In particular, the glass material used to take one of the liquids should not be used for another liquid. When preparing acid solutions, water should not be poured over the concentrated acid. The heating that occurs when water is added to the concentrated acid can cause sudden reactions. For this reason, concentrated acid should be slowly added to some water and mixed, and then it should be topped with distilled water. When using a pipette, the rubber bulb should be used. No solution or chemical should be taken by mouth. If a mixture to be separated from the precipitate is to be placed in the centrifuge, a tube containing the same volume of water or solution as the tube placed must be placed in the hole opposite the centrifuge hole so that the tube does not break. 1.2. Tools And Equipment Information Centrifuge Tube: They are cylindrical and Erlenmeyer tubes with a bottom made of plastic or glass, manufactured to withstand the pressure in the centrifuge, which is used to separate solids from liquids in the laboratory. Washing Bottles: Tap water is not used as water in the analytical chemistry laboratory. In the analytical chemistry laboratory, distilled water is used, which has been passed through ion- scavenging resins or distilled. This water is called "distilled water", "deionized" or "demineralized water". Solvents such as ethyl alcohol and acetone can be placed in the pistets in the laboratory, apart from distilled water. In this case, the washing bottles must be labeled and the name of the solvent in them must be written on the label. Beaker: It is a large, open-mouthed cylindrical glass or plastic container. It can be of different sizes. The volume lines on them are for informational purposes only and should not be used to measure volume. It is used for processes such as mixing, dissolving, heating. Erlenmeyer Flask: It is a Erlenmeyer-shaped glass container with narrow, neckless mouths and wide bottoms. It ensures that liquids are mixed well in it. Erlenmeyer flasks are used in the titration process. Measuring Cylinder: It is a graduated (divided), cylindrical glass or plastic material used to measure the volume of liquid. It is used to measure liquids that are too large to be drawn with a straw and transfer them to another place. Pipette: It is a graduated (divided) glass material that is used to take a certain volume of liquid from a solution. Very precise measurement can be made with pipettes. The point to be considered when using a straw is to cover the straw with the index finger, not the thumb. According to the order of precision of the rating on it, it is divided into A and B class. The most commonly used types of pipettes are; bull pipettes, Mohr (Graduated Pipettes), Micropipettes (Automatic Pipettes), Digital Pipettes. Burette: A burette is used for titrations and delivers a variable but accurately known volume. Your burette is composed of three major parts: The Barrel is the graduated tube used to hold your solution. The stopcock controls the rate of flow of solution out of the burette. The tip is carefully machined to deliver regular size drops. The burette is a delicate and expensive piece of glassware and should be handled carefully. If the burette is broken in any way, it is best to replace it. Each time before using your burette, check that there is no damage to the end of the burette tip. Any chips or cracks in a burette tip will have serious effects on the delivery of the titrant. Burets must be carefully washed with first tap water and distilled water. Glass Rod: It is a glass rod used for mixing and draining solutions. Watch Glass: It is a round glass material that closes the mouth of the beaker, Erlenmeyer flask and funnels and prevents dust and impurities from entering the air. Desiccator: It is a container made of glass with a lid containing moisture-retaining solids, which is used to store substances that absorb moisture from the air. It is also used as a cooler in gravimetric analysis so that the substances removed from the oven or oven do not absorb moisture until they are cooled. Funnel: It is a glass or plastic material used to filter liquids and transfer them to narrow containers. In the filtration process, qualitative or quantitative strainer papers are placed on them, depending on the purpose. Short-tube ones are preferred to filter solutions that crystallize immediately when cooled. Those with channeled inner surfaces are described as "quantitative funnels". Channels speed up the filtration process. During filtration, the sediment is covered with watch glass so that it is not contaminated with dust particles falling from the air. Gooch Crucible: It is a glass crucible that can be brought to fixed weighing with a self-strainer used to filter liquids. They are produced in 4 different pore sizes. The porous part, through which the filtration is carried out, is obtained by slightly softening the powdered glass with heat and gluing it together. While filtration with crucible, the solution is filtered under vacuum by connecting to a filtering Erlenmeyer flask with a vacuum outlet on the side with the help of an adapter. Volumetric Flask: To prepare a solution with exact concentration of a given solute, the solute must be weighed exactly and subsequently dissolved in an exact volume of solvent. For exact weighing the analytical balance is used and for dissolution in an exact volume a volumetric flask is used. 1.3. Evaluation and Laboratory Application Information Before coming to the laboratory, the experiment of the week should be studied and the questions at the end of the relevant section should be solved in the gaps left. In addition, a summary of the conduct of the experiment should be written weekly in the 'Student Notes' section, which is left blank in the sheet for each experiment before the practice lessons. These are prerequisites for entry into the laboratory. At the end of each experiment, there is a detailed table with student information and the date of each experiment, quiz grades, result calculation and result. Since this table will play an active role in calculating your laboratory performance grades, it will be checked on a weekly basis. The signature column will be filled in by the instructor/laboratory supervisor. When checking the experiment results, article 29 in the 'ANALYTICAL CHEMISTRY APPLICATION, SAFETY AND LABORATORY RULES' section is essential. Each experiment is evaluated as 100 full points. Students who find the correct result receive 100 full points from the performance part of that experiment. When calculating the experiment score of each week: Experiment result Completion of the experiment questions Quiz notes Parameters such as will be taken into account. At the end of the semester, the calculation of points and evaluation is done as follows. Exam Name Exam Content Percentage of impact MIDTERM EXAM 1. MIDTERM EXAM %12 TOPICS HOMEWORK %12 LABORATORY PERFORMANCE QUIZ %12 (2. MIDTERM EXAM) PRACTISE %24 PERFORMANCE ALL SUBJECTS GENERAL EXAM (BEFORE AND AFTER %40 MIDTERM EXAM) CHAPTER 2 - QUALITATIVE ANALYSIS 2.1. Basic Concepts in Qualitative Analysis Analytical Chemistry is the branch of science that examines the theoretical and experimental aspects of the methods used to determine the composition of a substance qualitatively and quantitatively. Qualitative analysis determines the components of an organic or inorganic substance, and quantitative analysis determines the amounts of these components. The method to be used in qualitative and quantitative analysis must meet the following conditions. a) The reaction must be specific and singular. b) The reaction should occur in one direction. c) The reaction should be fast. d) The end of the reaction should be easy to detect/observe. e) The reaction must be reproducible. Undoubtedly, the majority of chemical compounds are formed by the chemical bonding of a cation and an anion. Thus, if the cation and anion of such a molecule are identified by distinct procedures, it becomes feasible to predict the characteristics of the compound. Once the identity of the chemical is established, the quantity of the compound may be ascertained by the use of a specialized quantitative technique. Systematic qualitative analysis of cations refers to the process of identifying cations as positively charged ions by categorizing them. The systematic analytical approach of 23 cations developed by Fresenius, which has been employed in this section with several modifications, was first published in 1840 and has remained up-to-date until the present day. Cations are classified depending to the variability in solubilities among chloride, sulfur, hydroxide, carbonate, and phosphate salts. In the applied method, cations are first converted into chloride, sulfur, hydroxide, carbonate and phosphate salts with the appropriate precipitator, and after they are collected in 5 main groups, 4 of which precipitate with group precipitators and 1 dissolved, the cations in each group are separated from each other by distinguishing/unique features and defined one by one. The chemical formulas and colors of the precipitates formed by the precipitators of cation groups and precipitation media are seen collectively. Given below Table 2.1. Table 2.1. Groups of cations. Precipitation Formula and Color of Group Formula of Cations Properties Formed Sediments Precipitates into Ag+ AgCl (white) 1 chlorides with dilute Pb2+ PbCl2 (white) HCl. Hg22+ Hg2Cl2 (white) Hg2+ HgS (black) Cu2+ CuS (black) Bi3+ Bi2S3 (brown-black) Pb2+ PbS (black) Precipitates in the form Cd2+ CdS (yellow) of sulfides with H2S in As3+, As5+ As2S3 (yellow) 2 the medium with dilute HCl. As2S5 (yellow) Sb3+, Sb5+ Sb2S5 (orange) Sb2S3 (orange-red) Sn3+, Sn4+ SnS2 (yellow) SnS (brown) Al3+ Al(OH)3 (white) Precipitates as Cr3+ Cr(OH)3 (green) hydroxides with dilute NH3 solution in Fe3+ Fe(OH)3 (brown) presence of NH4Cl, Fe3+ Fe2S3 (black) 3 Precipitates in the form Mn2+ MnS (light pink) of sulfides with H2S in Ni2+ NiS (black) NH4Cl and dilute NH3 Co2+ CoS (black) medium. Zn2+ ZnS (white) In medium where NH3 Ba2+ BaCO3 (white) and NH4Cl is present, Sr2+ SrCO3 (white) precipitates in the form Ca2+ CaCO3 (white) of carbonates with (NH4)2CO3 solution. Mg2+ MgCO3 (white) 4 Ba2+ Ba3(PO4)2 (white) Or precipitates as phosphates with a Sr2+ Sr3(PO4)2 (white) solution of Ca2+ Ca3(PO4)2(white) (NH4)2HPO4 in a strong Mg2+ MgNH4PO4.6H2O (white) NH3 medium. NH4+ -------- There is no specific Na+ -------- 5 precipitator. K+ -------- CHAPTER 3 - HCl GROUP CATIONS (CATION I) A solid analysis sample containing cations of this group is dissolved in HNO3 (nitric acid or nitrate acid) medium. Or it is necessary to add a few drops of HNO3 on the sample given. If a dilute hydrochloric acid (HCl) solution is added to some solution taken from the sample, a white precipitate is formed. This precipitate contains chlorides of silver, lead-II, mercury-I and thallium-I cations. Therefore, these cations are called HCl group or first group cations. If the sample is not acidification with HNO3, chloride ions and salts with low solubility such as CuCl (Copper-I chloride) and AuCl (Gold-I chloride) can also precipitate. However, the addition of HNO3 prevents precipitation for them by providing oxidation. Additionally, the solubility of lead-II chloride (PbCl2), one of the cations of this group, is slightly higher (2.0x10- 2 mol/L). For this reason, it will not collapse completely, and after the separation of the precipitate, this ion must be re-searched in the remaining filtrate. Table 3.1. Ksp and solubility (mol/L) values of the first group of cation chlorides Compound Ksp Solubility (M) AgCl 1.6 x 10–10 1.3 x 10–5 Hg2Cl2 2.0 x 10–18 7.9 x 10–7 PbCl2 1.0 x 10–4 2.0 x 10–2 For qualitative recognition of the first group cations, it is necessary to know the reactions and properties of these ions with various reagents. For this purpose, each cation is examined separately below. 3.1. SILVER Silver is a metal that is bright white in color. It has a specific gravity of 10.50 g/cm3, a melting point of 950.5 oC and a boiling point of 1980 oC. Its electrical conductivity is enormous. It is a noble metal and is not affected by air. However, it can be oxidized with oxygen in hot. 2Ag + 1 2 O2 Ag2O 2Ag + H2S + 1 2 O2 Ag2S + H2O Metallic silver is not affected by non-oxidizing acids. It is soluble in HNO3 and hot solution of H2SO4 (sulfuric acid or sulfate acid). Ag + 2HNO3 AgNO3 + NO2 + H2O  2Ag + 2H2SO4 Ag2SO4 + SO2 + H2O Although silver has various oxidation steps such as Ag+, Ag2+, Ag3+, it is the Ag+ ion that can exist in a free state in the aqueous medium. Ag2+ and Ag3+ ions are mostly found in complex compounds. 3.1.1. Ag+ Ion Reactions a) HCl (chloride acid) solution If dilute HCl or alkaline chlorides are added to a solution containing silver ions, a white cheesy precipitate consisting of silver chloride (AgCl) is formed. Ag+(aq) + Cl-(aq) AgCl(s) (white) Although this silver chloride precipitate is insoluble in nitrate acid, it dissolves in excess of reagents such as concentrated chloride acid, NH3, sodium thiosulfate (Na2S2O3) and potassium cyanide (KCN), by giving complexes. AgCl(s) + HCl H+ + [AgCl2]- AgCl(s) + 2NH3 [Ag(NH3)2]+ + Cl- AgCl(s) + 2S2O32- [Ag(S2O3)2]3- + Cl- AgCl(s) + 2CN- [Ag(CN)2]- + Cl- b) NaBr and NaI solutions If NaBr or NaI solutions are dripped into the solution containing Ag+ ions with NH3, light yellow AgBr(s) and yellow AgI(s) precipitates are formed. Ag+ + Br- AgBr(s) (light yellow) Ag+ + I- AgI(s) (yellow) From these precipitates, AgBr is partially soluble in ammonia solution, while both AgBr and AgI precipitates are readily soluble in CN- and S2O32- solution, by giving complexes as above. c) NaOH solution When a solution of NaOH or KOH is added to a solution containing Ag+, a brown precipitate consisting of silver oxide is formed. 2Ag+ + 2OH- Ag2O(s) + H2O This precipitate, which is insoluble in the excess of the reagent, is easily soluble in acids, NH3, CN- and (NH4)2CO3 solutions. d) KCN solution Ag+ ions, together with CN- ions, firstly form a white-colored precipitate. However, this precipitate dissolves in excess of the reagent by giving complexes. Ag+ + CN- AgCN(s) (white) AgCN(s) + CN- [Ag(CN)2]- AgCN precipitate, which is insoluble in acids, dissolves in S2O32- solution, by giving it a complex. e) Na2S2O3 solution Silver ions are formed Ag2S2O3 by giving a white precipitate in the S2O3-2 solution. However, in excess of the reagent it dissolves by giving the precipitate complex. 2 Ag+ + S2O32- Ag2S2O3 (s) (white) Ag2S2O3 (s) + 3 S2O32- 2 [Ag(S2O3)2]3- On the other hand, the Ag2S2O3 precipitate that occurs before is not durable. The precipitate turns black over yellow-orange-brown over time and Ag2S is formed. Ag2S2O3 (s) + H2O Ag2S(s) + SO42- + 2H+ f) Potassium chromate (K2CrO4) solution A red-colored precipitate consisting of Ag2CrO4(s) is formed. This precipitate, which is insoluble in acidic environment, is soluble in NH3 solution. 2Ag+ + CrO42- Ag2CrO4(s) (red) Ag2CrO4 precipitate dissolves in dilute HNO3 solution by converting to Cr2O72- ion. 2 Ag2CrO4 (s) + 2H+ 4Ag+ + Cr2O72- + H2O g) Reductions Metals such as Zn, Cu, Fe, Mn or reducers such as FeSO4, MnSO4, N2H4, HCHO and NH2OH act on solutions containing Ag+ by releasing metallic silver at different pHs. 2Ag+ + Zn(s) Zn2+ + 2Ag(s) 2Ag+ + Mn2+ + 4OH- 2 Ag(s) + MnO2(s) + 2H2O 3.2. MERCURY It is found in the form of HgS (mercury-II sulfide) in nature. Mercury is a liquid metal at room conditions, with a freezing point of -39 oC and a boiling point of 357 oC. Mercury, whose vapors are monatomic, has a high specific gravity (d = 13.6 g/cm3). Mercury forms alloys with many metals called amalgams. Mercury is not affected by air and water in cold and is insoluble in HCl and H2SO4 solutions. But it is easily soluble in HNO3 solution. It dissolves in H2SO4 solution only at high temperatures. In these dissolution events, if the amount of acid in the environment is high, Hg2+ ions occur. Hg + 4HNO3 Hg(NO3)2 + 2NO2 + 2H2O 6Hg + 8HNO3 3Hg2(NO3)2 + 2NO + 4H2O Hg + 2H2SO4 HgSO4 + SO2 + 2H2O 2Hg + 2H2SO4 Hg2SO4 + SO2 + 2H2O 3.2. Hg22+ Ion Reactions a) HCl solution If a dilute solution containing Cl- ions is dropped into a dilute solution containing Hg22+ ion prepared with Hg2(NO3)2 salt, a white precipitate (calomel) consisting of Hg2Cl2 is formed. Unlike AgCl, this precipitate is soluble in HNO3. Hg22+ + 2HCl Hg2Cl2(s) + 2H+ 3Hg2Cl2(s) + 8HNO3 3HgCl2 + 3Hg(NO3)2 + 2NO + 4H2 On the other hand, if a few drops of NH3 solution are added on the Hg2Cl2 precipitate, a black precipitate consisting of mercury-II amidochloride (HgNH2Cl) and finely dispersed metallic mercury is formed. b) KI solution When KI solution is dripped into a solution containing Hg22+ ions, yellow-green colored Hg2I2 precipitates. This precipitate is insoluble in dilute acids. However, in excess of reagents, it dissolves by forming metallic mercury and complex as a result of disproportional. Hg22+ + 2I- Hg2I2 (s) Hg2I2 HgI2 + Hg  HgI2 + 2I- [HgI4]2- c) H2S solution In acidic solutions, a precipitate consisting of HgS and S is formed. The precipitate is completely soluble in gold water (aqua regia), while only the mercury part is soluble in the HNO3 solution. Hg22+ + H2S HgS(s) + Hg(s) + 2H+ d) NaOH solution Similarly, a black precipitate consisting of metallic mercury and mercury-II oxide occurs. Hg22+ + 2OH- Hg(s) + HgO(s) + H2O This precipitate, which is insoluble in the excess of the reagent, i.e. the mixture of Hg + HgO, is soluble in HNO3. e) KCN solution With disproportional, a mixture of Hg and mercury-II cyanide is formed. Hg22+ + 2CN- Hg(CN)2 + Hg(s) f) K2CrO4 solution In hot condition, it forms a precipitate consisting of mercury-I chromate (Hg2CrO4) in red color. Hg22+ + CrO42- Hg2CrO4(k) (red) If the reaction is to be carried out in the cold, an amorphous brown precipitate is formed first, and then when the precipitate is heated, it turns into red crystals. g) Reductions If a metal which is more electropositive than this ion is immersed in the solution containing the Hg22+ ion, metallic mercury is released. For example, if metallic copper wire is immersed in such a solution, the wire will be coated with mercury. Cu + Hg22+ Cu2+ + 2Hg(s) 3.3. LEAD Lead is a soft metal of blue-gray color and is easily made into metal plate. Its specific gravity is 11.49 g/cm3, melting point is 337.4 oC and boiling point is 1750 oC. Although the surface of the newly cutting lead metal is shiny, it becomes dull by being covered very quickly with an oxide layer in the air. Metallic lead is insoluble in dilute H2SO4 and halide acids (HCl, HF, HI, etc.). But it is easily soluble in nitrate acid and concentrated H2SO4 solution. 3Pb + 8HNO3 3Pb(NO3)2 + 2NO + 4H2O Pb + 3H2SO4 Pb+2 + 2HSO4- + SO2 + 2H2O Lead is insoluble in concentrated nitrate acid. Because the lead nitrate formed on the surface of the metal immersed in the HNO3 solution is insoluble in concentrated nitrate acid. In dilute solutions of HCl and H2SO4, lead chloride and sulfates, which are water-insoluble, occur on the surface of the metal. This, in turn, prevents further dissolution of the metal. 3.3.1. Pb2+ Ion Reactions a) HCl solution If a solution of dilute HCl or alkaline chloride is dripped onto a dissolved solution of lead-II salt, e.g., lead II nitrate, Pb(NO3)2, a white precipitate consisting of lead-II chloride is formed. Pb2+ + 2Cl- PbCl2(s) (white) The solubility of this precipitate (PbCl2) increases in direct proportion to temperature. That is, when the precipitate is heated, it dissolves and precipitation occurs again in the cooled solution. In addition, PbCl2 precipitate dissolves in excess of reagents by giving complexes. PbCl2(s) + 2Cl- [PbCl4]2- b) NaI solution When a solution containing iodide ions is dripped into a solution containing Pb2+ ions, lead iodide precipitate is formed in the form of yellow crystals. Pb2+ + 2I- PbI2(s) (yellow) The solubility of PbI2 also increases with temperature and dissolves in the excess of the reagent by giving complexes. PbI2(k) + 2I- [PbI4]2- c) H2S solution If a solution containing H2S is dripped into a solution containing lead ions, a black precipitate consisting of lead sulfide is formed. Pb2+ + H2S PbS(s) + 2H+ This reaction is very sensitive, and together with trace amounts of H2S are used to search for Pb2+. The formed PbS precipitate is easily soluble in nitrate acid. d) NaOH solution When sodium hydroxide solution is dripped into a solution containing lead ion, a white and voluminous precipitate is formed. Pb2+ + 2OH- Pb(OH)2(s) (white) While lead hydroxide precipitate dissolves with excess of sodium hydroxide in heated condition, it can be easily oxidized to PbO2 by oxidants such as hydrogen peroxide. Pb(OH)2 + H2O2 PbO2(s) + 2H2O This incoming, lead dioxide precipitate is insoluble in nitrate and sulfate acids, but soluble in hydrochloric acid. PbO2(s) + 4HCl PbCl2(s) + Cl2 + 2H2 e) H2SO4 solution Lead ions form lead sulfate precipitate in the form of white crystals with sulfate ions. Pb2+ + SO42- PbSO4(s) (white) While insoluble in dilute acids, this lead sulfate precipitate dissolves in solutions of ammonium tartrate, alkaline acetate by giving complexes, it is also soluble in concentrated sulfate and chloride acids. PbSO4(s) + 4HCl H2[PbCl4] + H2SO4 f) Na2CrO4 solution A yellow precipitate consisting of lead chromate is formed. This precipitate is insoluble in acetic acid and ammonia. Pb2+ + CrO42- PbCrO4(s) (yellow) Lead chromate precipitate is soluble in 6M NaOH and HNO3 solutions as lead cations.  PbCrO4 + 4OH- Pb(OH)42- + CrO42- 2PbCrO4 + 2H+ 2Pb2+ + Cr2O72- + H2O g) Dithizone solution With the dilute solution of dithizone in CCl4, a brick-red internal complex is formed in a neutral or ammonia medium. This reaction is very sensitive, and when the dilute dithizone solution is agitated with lead ion, the green color of the dithizone changes immediately. The presence of heavy metal cations such as Hg, Cu, Ag, Cd, Ni and Zn disrupts this reaction. However, their harmful effects are eliminated by adding excess potassium cyanide to the environment. 3.4. THALLIUM Thallium is found very little in nature and dispersed among other minerals such as zinc and lead. In terms of its properties, it is similar to lead. It is a shiny metal of bluish-white color. Its specific gravity is 11.8 g/cm3, melting point is 302 oC and boiling point 1457 oC. In humid air, the surface of the metal is covered with a layer of oxide. While thallium metal is soluble in nitrate and sulfate acids, it is hardly soluble in hydrochloric acid since the solubility of its chloride is low. 3.4.1. Tl+ Ion Reactions a) HCl solution If dilute chloride acid is added to the thallium nitrate solution, a white precipitate consisting of thallium chloride is formed. Tl+ + HCl TlCl(s) + H+ Thallium chloride precipitate is insoluble in ammonia like silver chloride by giving a complex. But it is easily soluble in thiosulfate solution. b) KI solution If KI is dripped little by little into the solution containing thallium ions, a yellow precipitate consisting of thallium iodide is formed. This precipitate is insoluble in NH3 and S2O32- solutions. Tl+ + I- TlI(s) (yellow) If the Tl3+ ion is present in the environment, I2 is released while it is reduced to the Tl+ ion during this reaction and the color of the medium becomes darker. Tl3+ + 3I- TlI + I2 c) H2S solution The reaction occurs in a weakly acidic or basic environment. The Tl+ ion forms the thallium sulfide precipitate with hydrogen sulfide solution. Tl+ + H2S Tl2S(s) + 2H+ 3.5. SYSTEMATIC ANALYSIS OF HCl GROUP CATIONS The sample given for analysis may be clear or turbid. If it is cloudy, the sample is shaken well and a 2-3 mL portion of it, which can be considered as homogeneous as possible, is taken into the centrifuge tube. 0.1 M hydrochloric acid is gradually dripped onto it. The first group cations that are likely to be found in this way are precipitated in the form of AgCl, PbCl2, Hg2Cl2 and TlCl. Among them, Pb2+ partially passes to the second group, since it does not precipitate quantitatively, and there it precipitates as PbSO4. The sample tube to which 0.1 M HCl has been added (3-5 drops) is shaken well and centrifuged for five minutes by placing it in a centrifuge. After the centrifugation stops, the sample tube is taken and a drop of 0.1 M HCl solution is dripped onto it. If there is no turbidity, precipitation is completed. Otherwise, after a few more drops of 0.1 M HCl solution are dripped, the tube is shaken, and then centrifuged again for 5 minutes. After the precipitation is completed, the upper solution phase is decanted and taken to another centrifuge tube. In order to wash the precipitate, a small amount of distilled water and 4-5 drops of 0.1 M HCl are added, respectively, the tube is shaken vigorously and centrifuged. During washing process, HCl is added to the washing water to reduce PbCl2 solubility by the common ion action, as it can be largely dissolved. The separated clear solution portion is centrifuged again and decanted and discarded. The remaining precipitate may contain AgCl, Hg2Cl2, PbCl2 and TlCl. Add 1-2 mL of hot distilled water to the precipitate in the tube, shake it and keep it in a water bath for 5 minutes. At this time, the mixture in the tube is thoroughly mixed with a glass rod or the tube is shaken frequently. Then, the hot tube is centrifuged. In this way, lead and thallium chlorides, which dissolve easily in heat, pass into the solution phase. Afterwards, these two cations are sought in the solution separated from the centrifuged tube by decanting. For this, sulfate acid is added to a part of the solution, and if any, lead is precipitated in the form of PbSO4 and separated. In the solution phase separated from here, Tl is searched with the help of KI. In order to recognize the lead remaining in the precipitation phase, ammonium acetate is added to it to dissolve the precipitate. In the resulting solution, Pb2+ ions are recognized by the solution of CrO42- or I-. In the first centrifugation process, the AgCl and/or Hg2Cl2 precipitate remaining in the tube is first thoroughly washed with hot water and completely purified from PbCl2 and TlCl. 1-2 mL of 10% NH3 solution is placed on it to dissolve the silver chloride as a complex. Meanwhile, mercury chloride turns into HgNH2Cl and forms a black precipitate, Thus, this process assert the presence of mercury. The presence of silver is proven by acidifying the solution phase with 0.1 M chloride acid to form the AgCl precipitate again or by dripping the KI solution and forming the yellow AgI precipitate.  SYSTEMATIC ANALYSIS OF HCl GROUP CATIONS A portion of 1-2 mL of the sample is taken into the centrifuge tube. Group I cations are precipitated in the form of chlorides by dripping 0.1 M HCl onto it. The formed precipitate is separated by centrifugation. Precipitate Solution Group I cations are sought in the Group cations II, III, IV and V are sought in the precipitate. solution. Precipitate The precipitate may contain AgCl (white), Hg2Cl2 (white), PbCl2 (white) and TlCl (white). Hot distilled water (1-2 mL) is added to the precipitate and shaken to provide the necessary dissolution. The mixture is centrifuged again. Precipitate Solution AgCl, Hg2Cl2 can be found in the 2+ + Pb , Tl cations are sought in solution. precipitate. First, the solution is cooled. 1-2 mL of 10% NH3 solution is added The Pb2+ ion remaining in the solution is to the precipitate. precipitated with the addition of H2SO4. It It is centrifuged to separate the is centrifuged to separate the precipitate. precipitate. Solution Precipitate Precipitate It may contain the Solution The resulting black The white Ag+ cation in The solution precipitate is Hg + precipitate is PbCl2 solution. may contain HgNH2Cl. and PbSO4. To prove the the Tl+ cation. The black precipitate It is dissolved by the presence of Ag+, one A KI solution is dissolved by addition of of the following two can be added dripping HNO3 NH4CH3COO on the methods can be used to the solution onto it. precipitate. One of after a drop of HNO3 solution to One of the following the following two is dripped into the prove the two methods can be methods can be used solution. presence of used to prove the to prove the presence of Hg22+. 1. AgCl is presence of Pb2+. Tl+. precipitated with the 1. Addition of CrO42- 1. Addition of addition of 0.1 M ion solution. CrO42- solution HCl solution. 2. Addition of I- ion 2. Addition of I- ion solution. 2. Yellow color AgI solution is formed with KI solution. QUESTIONS 1- Write down the reactions that occur between group I cations and HCl solution. 2- When group I cations are precipitated, it is necessary to use a dilute HCl solution. Concentrated HCl solution is not used. Why? Explain by writing reactions. 3- What is the reason for washing the precipitate with hot water in the process of recognition of the lead cation? 4- The Hg22+ ion is written differently than other ions with +1 oxidation steps (such as Ag+, K+). Explain its reason. 5- What are the suitable solvents that can dissolve AgCl, Hg2Cl2 and PbCl2 precipitates? Write reactions for these dissolvations. 6- What is disproportionation? Explain by giving an example. 7- Complete the following reactions. Indicate what kind of reaction the changes (reactions) that occur are. a) AgCl + Cl- → b) AgCl + CN- → c) AgCl + NH3 → d) Ag+ + Zn → e) Hg22+ + 2OH- → f) Pb + HNO3 → g) Hg22+ + SnCl2 + H+ → 8- Write an example of the reactions below. a) Reduction - oxidation reaction b) Precipitation reaction c) Complex formation reaction d) Dissolution reaction by complexation  HCl GROUP CATIONS (CATION I) – STUDENT NOTES Recognition Reactions: (The student should write one recognition reaction for each of the items sought in this section (available in the general information section of the sheet). Systematic Analysis Notes: (The student should simply summarize the systematic analysis steps to be followed in this section and schematize them in order to follow them during the experiment). Physical Changes: (In this section, the student should summarize and note the phenomena such as color change, temperature differences and gas release expected to be observed during the experiment).