Thermodynamics Quiz 1

An introductory quiz on Thermodynamics

1. Predict the change in entropy as positive or negative for the different scenarios

  1. Dissolving NH4Cl in water
  2. Sublimation of CO3(solid)
  3. Dissociation of Ammonia into nitrogen and hydrogen
  4. Condensation of water

2. The internal energy (ΔE) can be equal to the enthalpy (ΔH) of a system when

This is a multiple response question


3. The fish tank is an


4. Internal energy ΔE can be considered as


Question 1 of 4

Preparation of Tribromoaniline

Tribromo aniline can be prepared by dissolving aniline  in glacial acetic acid and then treating it with bromine dissolved in glacial acetic acid in the cold.

C6H5NH2 + 3Br2 => C6H2(Br)3NH2 (2,4,6-tribromoaniline)+ 3HBr

About 2 ml of aniline is dissolved in 5 mL of glacial acetic acid taken in an Erlenmeyer flask. The solution of bromine in glacial acetic acid is added in drops from a burette with constant stirring. Use a teflon coated magnetic stirrer for the purpose. The stirring should be continued until you get a pale yellow liquid.The mixture is then added to 75 mL of water. The crystallized 2,4,6-tribromoaniline is washed with cold water, dried and yield noted.About 1 gram of the sample can be recrystallized from dilute ethanol and melting point can be determined.

The approximate yield expected in this experiment is 3.0 grams and the melting point of the compound is 119oC.

Preparation of Benzoic acid from Benzamide

Benzamide is hydrolyzed to sodium benzoate by boiling with a sodium hydroxide solution. Sodium benzoate on acidification gives benzoic acid.
C6H5CONH2 + NaOH → C6H5COONa + HCl → C6H5COOH + NaCl
To prepare benzoic acid start with 3 grams of benzamide and mix it with 2 grams of sodium hydroxide dissolved in about 18 mL of water in a round bottom flask.. The flask is fitted with a Liebig’s condenser. The flask is heated on a wire gauze and the contents gently refluxed for about 50 minutes. Ammonia is evolved and the sodium salt of benzoic acid is formed in the solution. The flask is then cooled and the contents acidified with concentrated hydrochloric acid after transferring to a beaker. The precipitated benzoic acid is filtered using a Buschner funnel and the yield noted. About 1 gram can be recrystallized from hot water and the melting point can be determined to confirm the prepared compound.

Redox Titration

Potassium permanganate is a secondary standard and to standardize it, you can use ferrous ammonium sulfate ir Mohrs salt. Prepare a 0.1M Fe2+ solution pipette 10 ml into an erlenmeyer flask add 10 ML of 1M sulfuric acid and titration it against KMnO4 solution approximate concentration should be 0.02M. The end point is the Color change from clear to pale pink.

Titration Video