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Heat of Neutralisation - I am going to investigate the heat of neutralisation between acids and alkalis.

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Introduction

Heat of Neutralisation. I am going to investigate the heat of neutralisation between acids and alkalis. Prediction I predict that no matter what strong acid and alkali react together you will always get the same heat of neutralisation because the same reaction is always taking place. E.g. 1. HCl and NaOH 2. HNO3 and NaOH 3. NO3 and KOH 1. H++Cl�+Na+ + OH� Na++Cl� + H2O H+ + OH� H2O 2. H+ + NO3�+ Na++OH� Na+ + NO3�+ H2O H+ + OH� H2O 3. H+ + NO3� + K+ + OH� K+ + NO3� + H2O H++ OH� H2O I am also going to react 2 weak acids (ethanoic acid and propanoic acid) with a strong alkali (sodium hydroxide.) I predict that the energy change i.e. the heat of neutralisation will not be same as before because with weak acids and alkalis some energy is required to fully ionise them. Heat of neutralisation is the heat change when an acid and an alkali react together to form 1 mole of water. Fair Test To ensure the investigation is made fair I will always use the same concentration of acid and alkali (1 mole.) ...read more.

Middle

Repeat twice for each combination of acid and alkali to obtain accurate results that agree with each other 7. Record initial and maximum temperature in a table. Results ACID ALKALI INITIAL TEMP.(�C) MAX. TEMP. (�C) TEMP. RISE (�C) HCl NaOH 23 and 23 30 7 HCl NaOH 23 and 23 30 7 HCl KOH 23 and 23 30 7 HCl KOH 23 and 23 30 7 HNO3 NaOH 23 and 23 30 7 HNO3 NaOH 23 and 23 30 7 CH3COOH NaOH 23 and 23 28 5 CH3COOH NaOH 23 and 23 28 5 CH3CH2COOH NaOH 23 and 23 28 5 CH3CH2COOH NaOH 23 and 23 28 5 Heat of Neutralisations 1. HCl reacting with NaOH ?H= m x C x ? ?H= change in heat energy m = mass (always 50g) C = specific heat capacity (always 4.2 J/g/�C) ? = Temperature rise 25 x 1 moles = 50 x 4.2 x 7 kJ 1000 1000 0.025 moles = 1.47 1 mole = 1.47 0.025 = 58.8 The heat of neutralisation for hydrochloric acid reacting with sodium hydroxide is -58.8 kJ (negative because it is an exothermic reaction) ...read more.

Conclusion

The reason why you obtain the same heat of neutralisation when reacting a strong acid with a strong alkali is because the same reaction is always taking place, H + OH H2O An acid and an alkali react together to form 1 mole of water. I therefore from the results obtained I can conclude that you will always get the same heat of neutralisation if you react a strong acid with a strong alkali. Evaluation The 2nd/alternative method was certainly more accurate and reliable than the first as it took quicker to react because you didn't have to add 5cm3 then wait until you found the maximum temperature rise. The longer you take, the more heat can be lost. I feel confident to say that the results obtained were extremely accurate because:- 1. They matched my prediction 2. I got the same heat of neutralisation when reacting a strong acid with a strong alkali. However to back up the results one could carry out some further experiments. We could experiment with a larger range of acids and alkalis as I only used 4 different acids and 2 different alkalis. This would also support the results already obtained. We could also experiment with a different concentration as we only used acids and alkalis with a concentration of 1mol/dm-3. ...read more.

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Marked by teacher Kate Gardiner 17/10/2013

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