Determine the enthalpy of neutralization for HCl +NaOH, CH3COOH +NaOH, and 1/2H2SO4 +NaOH.

Apparatus- insulated calorimeter, dilute hydrochloric acid, dilute sulphuric acid, dilute ethanoic acid, aqueous sodium hydroxide, glass beakers, measuring cylinder, 25 cm3  pipette, thermometer, stirrer.

Method-

NaOH (aq) is taken as the limiting reactant in all the three reactions using a measuring cylinder.

Reaction one-

1. 25 cm3 of dilute hydrochloric acid (1.20M) is taken in a glass beaker using a 25- cm3 pipette.
2. The beaker was placed in an insulated calorimeter and the initial temperature recorded using a mercury thermometer.
3. 25 cm3 of a aqueous NaOH (1.04M) was added to the dilute HCl and the apparatus stirred after the lid was closed
4. Since the reaction is quick the thermometer was kept immersed into reaction mixture as soon as the NaOH (aq) was added to the hydrochloric acid through the opening on the lid of the insulated calorimeter. The final temperature was recorded.

Reaction 2-

1. 25 cm3 of dilute ethanoic acid (1.22M) is taken in a glass beaker using a 25-cm3 pipette.
2. The beaker was placed in an insulated calorimeter and the initial temperature recorded using a mercury thermometer.
3. 25 cm3 of a aqueous NaOH (1.04M) was added to the dilute HCl and the apparatus stirred after the lid was closed
4. Since the reaction is quick the thermometer was kept immersed into reaction mixture as soon as the NaOH (aq) was added to the hydrochloric acid through the opening on the lid of the insulated calorimeter. The final temperature was recorded.

Reaction 3-

1. 25 cm3 of dilute sulphuric acid (1.12M) is taken in a glass beaker using a 25-cm3 pipette.
2. The beaker was placed in an insulated calorimeter and the initial temperature recorded using a mercury thermometer.
3. 50 cm3 of a aqueous NaOH (1.04M) was added to the dilute HCl
4. The apparatus was stirred after the lid was closed
5. Since the reaction is quick the thermometer was kept immersed into reaction mixture as soon as the NaOH (aq) was added to the hydrochloric acid through the small opening on the lid of the insulated calorimeter. The final temperature was recorded.

After the following steps had been carried out the in each reaction the following step wee carried out

1. The heat evolved in the reaction was calculated using the equation

      Heat evolved in the reaction= heat gained by water

2. The enthalpy of neutralization was calculated using the equation

Heat gained by water/ no. of moles of the limiting reactant

                       

                     DATA COLLECTION AND PROCESSING

Results table

  Since there was no temperature change recorded, for the reaction of the ethanoic acid.   Thus the reaction was carried out again and the recordings taken again.

Heat absorbed by water= mass of water   x   sp. Heat capacity of water   x    change in temperature

For these reactions it is assumed that the acids have the same density and specific heat capacity as that of water.

Thus the enthalpy of neutralization each reaction= heat absorbed by water/no .of moles       of the limiting reactant

Since the temperature rises and the heat is given out all the three reactions are exothermic and thus enthalpy value will be negative.

 

Random error=+/-2.04

Conclusion and evaluation-

 The results that were obtained were near the literature value but the expected trend in the enthalpy of neutralization was not observed. The literature value for the enthalpy of neutralization for sulphuric acid and hydrochloric acid should be the same that is -57.3 KJ/mol. Hence the percentage of error is 17% and 30% respectively. The error for the enthalpy of neutralization (literature value 50.1) is 5.18%. In fact it is expected that the enthalpy of neutralization is the least for the reaction with ethanoic acid but this was not so. It could be due to the following reasons

• Some heat was lost to the surroundings due to which the final temperature was accurate.
• The apparatus was not adequately stirred.
• Since the reactions were quick it is possible that the thermometer was inserted after the reaction was over and thus the exact final temperature was not recorded.
• It is also assumed that the acids would have the same density and specific heat capacity as that of water which is not so. Hence this could cause a shift in the values

These errors could be minimized in the following ways

• The heat loss could be minimized by carrying out the experiment in a closed chamber to minimize the heat loss
• Care should be taken the apparatus was adequately stirred.