8Experiment E8: Endothermic and Exothermic Processes - Comprehensive Lab Notes

Objective: This series of experiments is designed to illustrate the fundamental chemical concepts of reaction heat ( $Enthalpie$ ) and entropy ( $Entropie$ ).
Institutional Context: Provided by the Institute for Chemistry and Biochemistry (Inorganic Chemistry Lab), specifically for the General and Inorganic Chemistry Internship.
Central Focus: Categorizing chemical reactions and physical processes by their energetic exchanges with the environment, specifically distinguishing between those that release heat and those that absorb it.

Key Research Areas: Students are required to consult textbooks to explore both chemical backgrounds and practical/historical facts regarding:
  - Aggregate states ( $Aggregatzustände$ ).
  - Dissolution processes ( $Lösungsvorgänge$ ).
  - Heat ( $Wärme$ ).
  - Enthalpy ( $Enthalpie$ ).
  - Entropy ( $Entropie$ ).
Original Literature Reference: For the endothermic reaction (Part 2), students should refer to: H. W. Roesky, K. Möckel, Chemische Kabinettstücke, VCH Verlagsgesellschaft mbH 1994, p. 219.
Research Question 1 (Exothermic Reaction): Identify the strongly exothermic reaction that occurs during "lime slaking" ( $Kalklöschen$ ) and identify its reaction type.
Research Question 2 (Endothermic Reaction): Explain why a strongly endothermic reaction can occur when mixing barium hydroxide ( $Ba(OH)_2 ∙ 8 H_2O$ ) and ammonium thiocyanate ( $NH_4SCN$ ), including identifying the reaction type.
Research Question 3 (Cold Mixtures): Describe the molecular-level processes of cold mixtures and explain how they achieve extremely low temperatures.
Equation Requirements: All relevant chemical equations must be formulated and understood for detailed explanation in a presentation.

Procedure: Place a small amount of calcium oxide ( $CaO$ ) into a small beaker and insert a digital thermometer. Carefully add a small amount of distilled water ( $H_2O$ ) and stir using the thermometer.
Safety Protocol: This must be performed in a fume hood ( $Abzug$ ) to protect against splashes.
Chemical Properties: Both calcium hydroxide ( $Ca(OH)_2$ ) and calcium oxide ( $CaO$ ) are strongly corrosive ( $ätzend$ ).

Procedure: Mix $10\,g$ of barium hydroxide octahydrate ( $Ba(OH)_2 ∙ 8 H_2O$ ) with $5\,g$ of ammonium thiocyanate ( $NH_4SCN$ ) in a small beaker.
The Freezing Test: Place the beaker on a moistened piece of solid cardboard ( $feste Pappe$ ) and stir the mixture with a digital thermometer.
Observation: Monitor the temperature change. After a short period, the temperature drops so significantly that the water under the beaker freezes, allowing the beaker to be lifted along with the frozen cardboard.
Hazard: Barium hydroxide is strongly corrosive.

a) Basic Ice-Water Mix: Combine ice and water in a beaker. Measure the temperature until it stabilizes; ensure a visible amount of ice remains.
b) Sodium Chloride/Ice Mix: Mix $5\,g$ of sodium chloride ( $NaCl$ ) with $10\,g$ of ice. Record the temperature. Students are encouraged to experiment with different ratios to achieve even lower temperatures.
c) Calcium Chloride/Ice Mix: Mix $14\,g$ of calcium chloride hexahydrate ( $CaCl_2 ∙ 6 H_2O$ ) with $10\,g$ of ice and measure the temperature.
d) Ethanol and Dry Ice: Under a fume hood, fill a small Dewar vessel with a maximum of $100\,ml$ of ethanol ( $EtOH$ ). Add dry ice ( $CO_2(s)$ ) until the temperature no longer changes. Larger pieces of dry ice must be crushed into powder beforehand (per assistant instructions).

Chemical Hazards: Students must research and be able to explain H and P statements (Hazard and Precautionary statements) in their own words for all materials.
Specific Warnings:
  - Corrosive Substances: $CaO$ , $Ca(OH)_2$ , and $Ba(OH)_2$ can cause severe chemical burns.
  - Flammability: Ethanol ( $EtOH$ ) is highly flammable.
  - Cryogenic Hazard: Contact with dry ice can cause cold burns (frostbite).
  - Dewar Vessels: These are evacuated glass containers and carry a risk of implosion.
Protective Equipment: Fume hood usage is mandatory for lime slaking and handling ethanol/dry ice.

Devices: Laborgerätestation (digital thermometer), beakers, spatulas.
Special Items: Piece of solid cardboard, small Dewar vessel (provided by teaching assistant).
Chemical Inventory:
  - Calcium oxide ( $CaO$ ).
  - Barium hydroxide octahydrate ( $Ba(OH)_2 ∙ 8 H_2O$ ).
  - Ammonium thiocyanate ( $NH_4SCN$ ).
  - Ice and distilled water ( $H_2O$ ).
  - Sodium chloride ( $NaCl$ ).
  - Calcium chloride hexahydrate ( $CaCl_2 ∙ 6 H_2O$ ).
  - Ethanol ( $EtOH$ ).
  - Dry ice (solid carbon dioxide).

Experiment 1 (Lime Slaking): After the mixture has cooled, it can be disposed of in the drain with a large volume of water. Caution: The mixture remains corrosive.
Experiment 2 (Barium Mixed Reaction): Dilute the beaker contents with a small amount of water and dispose of them in the aqueous heavy metal waste container ( $wässr. Schwermetallabfall$ ) located in the A-fume hood.
Experiment 3 (Cold Mixtures a-c): Salt/ice solutions are safe for drain disposal.
Experiment 3 (Cold Mixture d): Once the ethanol has warmed back to room temperature, dispose of it in the halogen-free solvent waste container ( $halogenfreier Lösungsmittelabfall$ ) in the O-fume hood. The lid of the waste canister should be left slightly unscrewed overnight to prevent pressure buildup and possible bloating of the container.

Laboratory Journal: All observations, exact weights ( $Einwaagen$ ), and conditions must be meticulously recorded.
Visual Evidence: Experimental setups should ideally be documented photographically.
Written Work: Students are required to produce formal written reports ("Versuchsvorschriften") for selected experiments, following a provided template.
Oral Presentation: Findings must be summarized in a short lecture during the introductory course. This talk should explain the theoretical concepts, practical procedures, and demonstrate the student's ability to explain chemical topics clearly.