Introductory Course in Inorganic Chemistry - Preparative Chemistry and Instrumental Analysis

General Information and Recommended Literature

• Course Schedule: The introductory course takes place on the days specified in the schedule from $1300\text{--}1800$ hours. Punctual attendance at all appointments is mandatory.

• Working Method: All work is conducted according to the provided script.

• Standard Textbooks:

  • G. Jander and E. Blasius: Lehrbuch der analytischen und präparativen anorganischen Chemie, S. Hirzel Verlag Stuttgart.

  • E. Riedel: Anorganische Chemie, de Gruyter Verlag Berlin, New York.

  • G. Brauer (Ed.): Handbuch der Präparativen Anorganischen Chemie (in 3 volumes), F. Enke Verlag Stuttgart.

Preparative Work Techniques and Laboratory Organization

• Equipment and Safety: During the course, essential laboratory equipment and techniques for preparation are introduced. Special attention must be paid to safety instructions regarding the use of membrane pumps and evacuated apparatuses.

• Chemical Supply: Chemicals are organized in boxes located at the assistant's distribution point. Some chemicals may also be found in the "one-set" or "five-set," or in fume hoods A and O.

• Self-Reliant Work: In the open laboratory, students prepare samples independently with support from assistants.

• Storage and Characterization: Preparations are collected in sample vials (if air-stable). Some preparations are characterized using analytical methods.

  • Chemistry-Mono Students: Access to the IR spectrometer in Room F07 is granted after instruction. One preparation must be investigated using elemental analysis.

• General Conduct Guidelines:

  • If a synthesis fails, time is provided for repetition.

  • Accurate recording of weights and measured values is required.

  • Self-critical error analysis is expected (e.g., checking preparation quality or equipment cleanliness).

  • In case of technical difficulties (e.g., filtration failure), students should consult assistants or tutors rather than using technical errors as an excuse for failed experiments.

Laboratory Orientation and Specialized Areas

• Fume Hoods and Pumps: Used for handling hazardous gases and for vacuum filtration (under-pressure filtration).

• Chemical Boxes: Specific boxes labeled with experiment titles are located at the distribution point. Box numbers do not correspond to Blackboard experiment numbers.

  • Special Boxes: Distinct boxes exist for toxins ("Giftkiste") and metal powders ("Metallpulverkiste").

  • Protocol: Bottles must be returned to their correct box immediately after weighing.

• Weighing Stations: Scales must be kept clean at all times.

• Specialized Equipment: Magnetic stirrers and other special devices are kept in specific areas (e.g., 2nd-floor windowsills or 4th-floor equipment stations). They must be returned clean. Note: Magnetic stirrers with heating plates must be allowed to cool in a safe location before being returned.

• Filtration Equipment:

  • 1 = Matching round filter ($5.5\,cm$ diameter).

  • 2 = Büchner funnel (detachable for cleaning).

  • 3 = Rubber gasket (Gummimanschette).

  • 4 = $100\,ml$ suction flask (Saugflasche).

  • A PVC hose connects the suction flask to the membrane pump.

  • Crucial Note on Filters: Pre-cut filters for $5.5\,cm$ diameter funnels are provided. Do not cut larger papers to size, as this causes filtration failure.

Demonstration of Standard Techniques

2.1 Stirring and Dropping

• Apparatus Assembly: Includes a dropping funnel with pressure equalization, a single-neck flask ($250\,ml$), a magnetic stirrer, and a magnetic stirring bar.

• Procedure: Preparation of $30\%$ sulfuric acid. Concentrated sulfuric acid is added from the dropping funnel into a calculated amount of water while stirring.

• Calculation: Quantities are determined using the mixing cross (Mischungskreuz) taught in the first tutorial session.

2.2 Reflux Boiling and Recrystallization

• Principle: A substance that is poorly soluble in the cold but soluble when heated is dissolved in a solvent (e.g., water). Upon cooling, the pure substance crystallizes while impurities remain in the solution (solubility product not exceeded).

• Apparatus: Single-neck flask ($500\,ml$, NS 29) with an attached reflux condenser, stirrer, and heating source.

• Procedure: A water bath (crystallization dish filled with water pre-boiled in a laboratory kettle) is used on a heating plate. The flask is immersed in the water bath.

  • The reflux condenser acts as an air condenser in this specific demo; otherwise, cooling liquid is circulated through the coils.

Show Experiment: Aluminothermic Reduction (Thermit)

• Reaction Principle: Reduction of metal oxides/sulfides with finely divided aluminum based on the high heat of formation of $Al_2O_3$.

• Temperature Range: Between $2000\,^\circ C$ and $2500\,^\circ C$.

• Outcome: Metals produced are usually brittle and alloyed with approximately $1\%$ aluminum.

• Safety: Must be supervised by an assistant and performed outdoors. Cancelled in rain or snow. Students must maintain several meters of distance and avoid looking directly into the flame.

• Materials (Box 1):

  • Aluminum grit (Al-Grieß).

  • Iron(III) oxide ($Fe_2O_3$).

  • Barium peroxide ($BaO_2$).

  • Magnesium powder ($Mg$-Pulver).

  • Flower pot (with bottom hole), sparkler, aluminum foil, and leather glove.

• Mixing Ratios:

  • Thermite mixture: $60\,g$ $Fe_2O_3$ mixed with $15\,g$ aluminum grit in a $250\,ml$ screw-cap container.

  • Ignition mixture: $0.75\,g$ $BaO_2$ and $0.75\,g$ $Mg$ powder mixed in a snap-lid vial (caution: never use a mortar/pestle due to explosion risk).

• Execution: The flower pot hole is sealed with paper. The Thermite is pressed in, and a hole is made in the center for the sparkler and ignition mix. The pot is wrapped in foil. After the reaction, magnetism can be demonstrated on the cooled iron using a magnetic stirring bar.

• Disposal: Cooled pots wrapped in foil are placed in contaminated waste bags (Fume hood A).

Practice Preparation 4.1: Recrystallization of Potassium Hydrogen Tartrate (Weinstein)

• Synthesis Step: $1.5\,g$ tartaric acid (Weinsäure), $0.5\,g$ $KOH$, and $10\,ml$ deionized water are mixed in a test tube. The suspension is stirred with a glass rod and centrifuged.

• Recrystallization Step: Raw salt products from all groups are combined in a $500\,ml$ flask. Hot distilled water (from lab kettle) is added while stirring and heating until a clear solution forms. The solution is allowed to cool slowly.

• Solubility of $KHC_4H_4O_6$:

  • $0.389\,g/l$ at $11\,^\circ C$.

  • $5.85\,g/l$ at $100\,^\circ C$.

• Note: If the mixture does not boil quickly on the plate, a burner/tripod/ceramic plate may be used to demonstrate higher heating efficiency.

• Disposal: Solutions go down the drain. Residue on glass can be removed with acid (e.g., $9\%$ sulfuric acid).

Practice Preparation 4.2: Synthesis of Prussian Blue

• Chemical Formula: $Fe_4[Fe(CN)_6]_3$

• Procedure: $1\,g$ potassium hexacyanoferrate(II) trihydrate is dissolved in $10\,ml$ distilled water. This yellow solution is mixed with a solution of $2\,g$ iron(III) chloride hexahydrate in $5\,ml$ distilled water.

• Filtration Technique: The fine powder is filtered using a Büchner funnel. The filter paper is first wetted with water while the pump is on to ensure a tight seal. The substance is added in small portions to the center.

• Properties: Deep blue crystals, poorly soluble in water/organic solvents. Unstable against strong acids and bases.

  • DANGER: Heating with strong acids can release highly toxic hydrogen cyanide (Blausäure).

• Disposal: Suspend solid in water, add $2\,M$ $NaOH$ until the blue disappears (replaced by brown iron(III) hydroxide). Dispose of as aqueous heavy metal waste (Fume hood A). Clean equipment with soda solution (sodium carbonate).

Practice Preparation 4.3: Synthesis and Micro-Scale Recrystallization of Copper(II) Sulfate

• Chemical Formula: $CuSO_4 \cdot 5 H_2O$

• Synthesis: $1\,g$ copper(II) oxide is reacted with $15\,ml$ of $9\%$ sulfuric acid. Boil using burner/tripod until fully dissolved.

• Safety Warning: Work under the fume hood. Do not let the solution evaporate to dryness, as this produces toxic, respiratory-irritating $SO_3$.

• Processing: Concentration to $5\,ml$ via heating in a porcelain dish. Precipitation is induced by adding an ethanol-water mixture ($1:1$) and cooling. Filter via Büchner funnel.

• Recrystallization: Place raw product in a test tube with very little deionized water (most salt must remain undissolved). Heat in a bunsen burner flame until dissolved, then pour quickly onto a watch glass to observe crystallization.

• Solubility: $203\,g/l$ in water at $20\,^\circ C$.

• Disposal: Solid and filtrates go to aqueous heavy metal waste (Fume hood A). Anhydrous organic solvents go to the organic waste (Fume hood O).

Specialized Analysis (Chemistry-Mono Only)

5. Vibrational Spectroscopy (ATR-IR)

• Includes theoretical background of vibrational spectroscopy.

• Practical instruction on ATR-IR spectrometer operation and spectrum interpretation.

6. Elemental Analysis

• Required for:

  • Mohr's Salt: $(NH_4)_2Fe(SO_4)_2 \cdot 6 H_2O$

  • Iron(II) chloride tetrahydrate: $FeCl_2 \cdot 4 H_2O$

  • Zinc(II) orthophosphate tetrahydrate: $Zn_3(PO_4)_2 \cdot 4 H_2O$

• Methods: Iron content via permanganometric titration; Zinc content via complexometric titration.

• Disposal Note: Surplus $KMnO_4$ must be reduced with hydrogen peroxide and concentrated sulfuric acid until colorless ($Mn^{2+}$) before disposal in heavy metal waste.

Seminar Presentations and Evaluation

• Format: Short presentations ($2\text{--}3$ people) using PowerPoint. Must cover chemical background and safety (hazardous substances/techniques).

• Evaluation Criteria (Percentages):

  • Presentation and Slides (20%): Media usage, creativity, readability, structuring.

  • Presentation Style (20%): Motivation, coordination between speakers, structure.

  • Content Understanding/Q&A (60%): Depth of research, correctness of presentation, ability to answer questions from peers and assistants.

• Presentation Structure:

  1. Introduction: Focused, not general Wikipedia-style rambling.

  2. Reaction Equations: Detailed equations (e.g., redox half-equations). Explain the role of every substance (oxidant, pH buffer, etc.). Use dissociated formulas for aqueous solutions (e.g., $[Co(H_2O)_6]^{2+}$ instead of $CoCl_2 \cdot 6 H_2O$).

  3. Practical Aspects: Schematic procedure (avoid exact gram values in talk), experimental setup sketches, and specific hazards (relevant H/P context, not just reading lists).

Mini-Publication (Final Lab Report) Guidelines

• Submission Format: Printed copy and a PDF file sent to the assistant.

• Structure for Preparations:

  1. Introduction: General and specific to the preparation/synthesis.

  2. Experimental Part: Self-written synthesis (not copy-pasted), yield calculation (detailed showing of molar amounts), characterization (IR spectroscopy and Elemental Analysis including titration reactions/calculations).

  3. Summary.

  4. Literature Reference List.

  5. Appendix (Spectra).

• Formatting Requirements:

  • Font size 12, 1.5 line spacing.

  • Clean mathematical/chemical formulas (use formula editors; use subscripts/superscripts correctly).

  • High-resolution graphics, numbered and cited.

  • Proper grammar, spelling, and scientific terminology (no laboratory jargon).

  • All deviations from expected results must be discussed.

• Evaluation Categories:

  • Form, Structure, and Citations: $20\%$.

  • Evaluation of Results and Summary: $20\%$.

  • Theory part and additional questions: $60\%$.

• Plagiarism Warning: Plagiarism (including use of "old protocols") is treated as fraud. All sources must be linked and cited at the points used in the text.