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IV. Heat of reaction of a weak acid with weak base Total mass of solution Final temp. of solution Initial temp. of solutions AT Water AH reaction 40 9 29 C 22"C Calculation: Heat of reaction per mole water formed Moles of water formed AH reaction per mole H,O formed Calculation Heat of dissociation of weak acid and weak base AH dissociation (per mole)- Calculation: [AH Dissociation- AH reaction -AH Neutralization (from II)] IV. Enthalpy of Neutralization of a Weak Acid and a Weak Base Unlike a strong acids and bases, weak acids, and bases, are not completely dissociated in solution. The reaction can therefore be considered a two-step process. The first step is the dissociation of the weak acid and weak base, then the hydroxide and hydronium ions neutralize. The reactions are: (I) NH,OH + НСНО, →NFI,' + ОН + H' + C,H,02_ (dissociation) (Neutralization) The net enthalpy change can be determined using the same procedure that was used in the previous section. The net enthalpy change for the reaction, AH(reaction) is the sum of the enthalpy changes for dissociation and neutralization dH(reaction) ΔΗ(dissociation ) + dH (neutralization) Notice that the neutralization step has the same net ionic equation as the previous section. Since the enthalpy change for that is known, the AH(dissociation) can be calculated once ΔΗ (reaction) has been determined. Procedure 1 . Pour about 20 ml of 1 .0 M HC.НО, into a styrofoam coffee cup. Add 5 drops of phenolphthalein indicator. This allows visual verification of neutralization of the acid. 2. Pour 20.0 ml of 1.1MNHOH into a small beaker2c 3. Adjust the temperature of the two solutions so that they are equal. Place the beaker of NH,OH in hot or cold water to raise or lower its temperature. Record the initial temperature of each solution Pour the NH,OH solution into the HC,H,O, solution in the cup. Stir gently with the thermometer, and observe the temperature. Record the temperature when is stops changing. This is the final temperatureo Dispose of the solution down the drain and rinse the cup with water 4. 5. The calculations are similar to those in the previous section: Determine the enthalpy of the net reaction. Using the stoichiometry of the reaction, determine the moles of water formed, and calculate the enthalpy of neutralization per mole of water formed. a. b. c. Using the molar enthalpy of reaction and the molar enthalpy of neutralization (from part III) determine the enthalpy of dissociation. าก

Answer 1

Ven Moss of Nao!30 g 23 Iniial temp CT) 22 Again, 5928.3 J.