CHEM121 General Chemistry Lab – I Fall 2024 PDF

KADİR HAS UNIVERSITY FACULTY OF ENGINEERING AND NATURAL SCIENCES CHEM121 General Chemistry Lab – I FALL 2024 PREPARED BY Dr. M. Mustafa Cetin Technical Specialist Mine Cengiz Cetin EXPERIMENT 2 THE IDENTIFICATION OF I...

KADİR HAS UNIVERSITY FACULTY OF ENGINEERING AND NATURAL SCIENCES CHEM121 General Chemistry Lab – I FALL 2024 PREPARED BY Dr. M. Mustafa Cetin Technical Specialist Mine Cengiz Cetin EXPERIMENT 2 THE IDENTIFICATION OF IONS BY THEIR PROPERTIES PURPOSE Identification of some important ions by means of their reactions with different chemicals. Before You Come to Lab Read the entire lab manual, including the introduction and discussion, and the entire procedure. Complete the Pre-Lab below and turn the pre-lab into your instructor/TA with your report. PRE-LAB QUESTIONS 1. Explain these terms in your own words; a. Anion and cation. b. Precipitate. c. Soluble. d. Aqueous. e. Miscible and immiscible. 2. What kinds of elements generally form ionic compounds? 3. Write the short-hand electron configuration of Cu first and then use this to produce the short- hand electron configurations for Cu+ and Cu2+ ions. INTRODUCTION This experiment will analyze known solutions for the presence of specific cations and anions. The general approach to finding out what ions are in a solution is to test for the presence of each possible component by adding a reagent that will cause that component, if present, to react in a certain way. This method involves a series of tests, one for each component, carried out on separate samples of solution. Difficulty sometimes arises, particularly in complex mixtures, because one of the species may interfere with the analytical test for another. Although interferences are common, many ions in mixtures can usually be identified by simple tests. If electrons are removed from or added to an atom, a charged particle called an ion is formed. An ion with a positive charge is a cation; a negatively charged ion is an anion (Figure 1). Figure 1. Ion Formation. To see how ions form, consider the sodium (Na) atom, which has 11 protons and 11 electrons. If this atom loses one (1) electron, the resulting cation has 11 protons and 10 electrons, which means it has a net charge of 1+ (Figure 2).  1s2 2s2 2p6 3s1 1s2 2s2 2p6 Figure 2. Electron Configuration of Sodium Atom and Sodium Ion. The net charge on an ion is represented by a superscript. The superscripts +, 2+, and 3+, for instance, mean a net charge resulting from the loss of one, two, and three electrons, respectively. The superscripts –, 2–, and 3– represent net charges resulting from the gain of one, two, and three electrons, respectively. Chlorine, with 17 protons and 17 electrons, for example, can gain an electron in chemical reactions, producing the Cl¯ ion (Figure 3). 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6 Figure 3. Electron Configuration of Chlorine Atom and Chlorine Ion. In general, metal atom stent to lose electrons to form cations and nonmetal atom stent to gain electrons to form anions. Thus, ionic compounds tend to be composed of both metal cations and nonmetal anions, as in NaCl (Scheme 1). 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 Figure 3. Sodium and Chloride Ions Forming NaCl. In addition to simple ions such as Na+ and Cl¯, there are polyatomic ions, such as NH4+ (ammonium ion) and SO42- (sulfate ion), which consist of atoms joined as in a molecule, but carrying a net positive or negative charge. SAFETY CONSIDERATIONS Safety in the Laboratory Sodium hydroxide (NaOH) solution is corrosive, can cause chemical burns to the skin, and care is necessary when using this reagent. You must follow all the special safety directives you will receive in the laboratory to protect yourself. If the sodium hydroxide (NaOH) solution contacts your skin, flush the affected area with water for five (5) minutes. Nitric acid (HNO3) is corrosive and can cause chemical burns to the skin. Special care is necessary when using these reagents. If any nitric acid contacts your skin, flush the affected area with water for five minutes. Barium chloride (BaCl2) is toxic. Ba2+(aq) cannot be allowed to go down the drain. Carefully follow all instructions for chemical waste disposal. Ammonia (NH3) is caustic. Avoid inhaling the ammonia fumes. Avoid splashing on your skin, in your eyes, or in your mouth. Fe3+ other heavy metal ion cannot be allowed to go down the drain. Carefully follow all instructions for chemical waste disposal. Nitrogen (N2) and carbon dioxide (CO2) gases are released as reaction product. Therefore, it should be worked under a fume hood. Silver nitrate (AgNO3) can stain skin and clothing. Waste Disposal and Cleanup All solutions should properly be poured into the waste collection bucket provided. Before You Leave the Lab Have your instructor/TA check your lab bench for cleanup. Get your data sheet to be signed by your instructor/TA. Wash your hands before leaving the lab. MATERIALS Phosphate Ion (PO43–) Solution Test Tubes Ammonium Molybdate Acidified Test Tube-Rack Sulfate Ion (SO42-) Solution Test Tube Holder Barium Chloride (BaCl2) Solution Beakers Thiosulfate Ion (S2O32-) Solution Erlenmeyer Flasks Silver Nitrate (AgNO3) Solution Pasteur Pipettes Nitrite Ion (NO2¯) Solution Glass Stirring Rods Urea (CO(NH2)2) Solution Hot Water Bath Chloride Ion (Cl–) Solution Bromide Ion (Br¯) Solution Sodium Hydroxide Solution (NaOH) Iron(III) Solution (Fe3+) Sodium Hydrogen Phosphate (Na2HPO4) Solution Sodium Acetate (CH3COONa) Aluminum Ion (Al3+) Solution Chromium(III) Ion (Cr3+) Solution Ammonia (NH3) Solution 1.5 M Nitric Acid (HNO3) PROCEDURE PART A. Characteristic reaction of the phosphate ion (PO4 3–) PO3− 4(aq) + 12(NH4 )2 MoO4(aq) + 21HNO3(aq) → (NH4 )3 [P(Mo3 O10 )4 ](s) + 21NH4 NO3(aq) + 12H2 O(l) 1. 1 mL solution containing of phosphate ion is transferred into a clean and dry test tube and 4 mL solution of ammonium molybdate acidified with nitric acid is added. 2. The solution is heated 1 or 2 minutes in a hot water bath (40°C). 3. A characteristic yellow precipitate of ammonium phosphomolybdate is obtained. PART B. Characteristic reaction of the sulfate ion (SO42–) BaCl2(aq) + SO2− − 4(aq) → BaSO4(s) + 2Cl(aq) 1. A few mL solutions containing sulfate ion is put into a clean and dry test tube. 2. The barium chloride solution is added dropwise and with stirring. 3. If the white precipitate is formed, it indicates the sulfate ion. 4. Barium sulfate is not soluble in dilute hydrochloric acid and nitric acid. PART C. Characteristic reaction of the thiosulfate ion (S2O32–) S2 O2− − 3(aq) + 2AgNO3(aq) → Ag 2 S2 O3(s) + 2NO3(aq) 1. A few mL solutions containing thiosulfate ion is put into a clean and dry test tube silver nitrate is added. 2. A white silver thiosulfate precipitate is formed as a result of the reaction. 3. A white silver thiosulfate which dissolves in excess thiosulfate by formation of a thiosulfate complex ion, precipitates. AgS2 O3(aq) + 3S2 O2− 3− 3(aq) → 2[Ag(S2 O3 )2 ](aq) 4. Silver thiosulfate is an unstable compound which forms black silver sulfide when heated. Ag 2 S2 O3(s) + H2 O(l) → Ag 2 S(s) + H2 SO4(aq) PART D. Characteristic reaction of the nitrite ion (NO2¯) H+ CO(NH2 )2(aq) + 2HNO2(aq) → 2N2(g) + CO2(g) + H2 O(l) 1. A few mL samples containing nitrite ion is put into a clean and dry test tube and a few mL of urea solution is added after the sample is acidified with 1.5 M nitric acid (HNO3) solution. 2. Nitrites oxidize urea to carbon dioxide and are themselves reduced to nitrogen gas. PART E. Characteristic reaction of the chloride ion (Cl–) AgNO3(aq) + Cl− → AgCl(s) + NO− 3(aq) 1. A few mL samples containing chloride ion is put into a clean and dry test tube and a few mL of silver nitrate solution is added. 2. The formation of a white curdy precipitate of silver chloride is observed. 3. Silver chloride is insoluble in strong acids and bases. Silver chloride is soluble in solutions containing diluted ammonia, potassium cyanide, and sodium thiosulfate. AgCl(s) + 2NH3(aq) → [Ag(NH3 )2 ]+ − (aq) + Cl(aq) [Ag(NH3 )2 ]+ − (aq) + Cl(aq) + 2HNO3(aq) → AgCl(s) + NH4 NO3(aq) PART F. Characteristic reaction of the bromide ion (Br¯) − Br(aq) + AgNO3(aq) → AgBr(s) + NO− 3(aq) 1. A few mL solutions containing bromide ion is put into a clean and dry test tube and silver nitrate is added. 2. As a result of the reaction, a yellow silver bromide precipitate is formed. 3. This precipitate dissolves in solutions containing concentrated ammonia, potassium cyanide, and potassium thiosulfate. It is not soluble in nitric acid. PART G. Characteristic reaction of the iron(III) ion (Fe3+) Fe3+ 2− + (aq) + HPO4(aq) → FePO4(s) + H(aq) HPO2− + 4(aq) + H(aq) → H2 PO4(aq) Fe3+ 2− − (aq) + 2HPO4 → FePO4(s) + H2 PO4(aq) Fe3+ 2− − (aq) + HPO4(aq) + CH3 COO(aq) → FePO4(s) + CH3 COOH(aq) 1. A few mL of solution containing iron(III) ions is put into a clean and dry test tube. Yellowish iron(III) phosphate is precipitated by adding excess disodium phosphate. 2. In order to obtain complete precipitation of iron(III) ions as iron(III) phosphate, sodium acetate (CH3COONa) is added into the tube to prevent the release of hydrogen ions. PART H. Characteristic reaction of the aluminum ion (Al3+) Al3+ − (aq) + 3OH(aq) → Al(OH)3(s) 1. A few mL solutions containing aluminum(III) ions put into a clean and dry test tube and sodium hydroxide is added into the solution. 2. A white, gelatinous precipitate of aluminum hydroxide which dissolves very easily in excess reagent is obtained. 3. This precipitate is soluble in acids and bases due to amphoteric character of aluminum hydroxide. − Al(OH)3(s) + OH(aq) → Al(OH)− 4(aq) + Al(OH)3(S) + 3H(aq) → Al3+ (aq) + 3H2 O(l) PART I. Characteristic reaction of the chromium ion (Cr3+) 3+ + Cr(aq) + 3NH3(aq) + 3H2 O(l) → Cr(OH)3(s) + 3NH4(aq) 1. A few mL solutions containing chromium ions is put into a clean and dry test tube and ammonia solution is added. 2. A gelatinous, gray-green, or gray-blue precipitate, chromium(III) hydroxide, is obtained. 3. In excess ammonia, some dissolving also occurs, yielding a pink or violet complex ion. On boiling a solution of complex, chromium(III) hydroxide reprecipitates. Cr(OH)3(S) + 6NH3(aq) → [Cr(NH3 )6 ]3+ − (aq) + OH(aq) DATA & ANALYSIS Part A. Characteristic reaction of the phosphate ion (PO43–) Equation: PO3− 4(aq) + 12(NH4 )2 MoO4(aq) + 21HNO3(aq) → (NH4 )3 [P(Mo3 O10 )4 ](s) + 21NH4 NO3(aq) + 12H2 O(l) Observation:…………………………………………………………………………… Part B. Characteristic reaction of the sulfate ion (SO42–) Equation: BaCl2(aq) + SO2− − 4(aq) → BaSO4(s) + 2Cl(aq) Observation:……………………………………………………………………………. Part C. Characteristic reaction of the thiosulfate ion (S2O32–) Equation: S2 O2− − 3(aq) + 2AgNO3(aq) → Ag 2 S2 O3(s) + 2NO3(aq) Observation:…………………………………………………………………………………… Part D. Characteristic reaction of the nitrite ion (NO2¯ ) H+ Equation: CO(NH2 )2(aq) + 2HNO2(aq) → 2N2(g) + CO2(g) + H2 O(l) Observation:……………………………………………………………………………………. Part E. Characteristic reaction of the chloride ion (Cl¯ ) − Equation: AgNO3(aq) + Cl− → AgCl(s) + NO3(aq) Observation:…………………………………………………………………………………….. Part F. Characteristic reaction of the bromide ion (Br¯ ) − Equation: Br(aq) + AgNO3(aq) → AgBr(s) + NO− 3(aq) Observation:……………………………………………………………………………………. Part G. Characteristic reaction of the iron(III) ion (Fe3+) Equation: Fe3+ 2− + (aq) + HPO4(aq) → FePO4(s) + H(aq) HPO2− + 4(aq) + H(aq) → H2 PO4(aq) Fe3+ 2− − (aq) + 2HPO4 → FePO4(s) + H2 PO4(aq) Fe3+ 2− − (aq) + HPO4(aq) + CH3 COO(aq) → FePO4(s) + CH3 COOH(aq) Observation:………………………………………………………………………………… Part H. Characteristic reaction of the aluminum (Al3+) ion Equation: Al3+ − (aq) + 3OH(aq) → Al(OH)3(s) Observation:…………………………………………………………………………………….. Part I. Characteristic reaction of the chromium ion (Cr3+) 3+ + Equation: Cr(aq) + 3NH3(aq) + 3H2 O(l) → Cr(OH)3(s) + 3NH4(aq) Observation:………………………………………………………………………………… POST-LAB QUESTIONS The post-lab questions will be posted to the LEARN platform in the Lab Report Template.