An Investigation into the Heat of Neutralisation

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Laura Davies  Chemistry Coursework

An Investigation into the Heat of Neutralisation


Aim: the aim of this investigation is to look at what effect concentration has on the temperature and energy changes in a neutralisation reaction.

Introduction: Neutralisation occurs when an acid and an alkali base are reacted together to form a neutral solution. Despite this, a neutral solution will only be achieved if the alkali and acid are of equal strength. This occurs because the H+ ion in the acid reacts with the OH¯ ion in the alkali to form H20 or water, which is neutral. The H+ ions are destroyed when they are reacted with a carbonate or metal base. The OH¯ ions are destroyed when they are reacted with an acid. The equation for this is shown as follows:

H+        +       OH¯                            H20

However alkalis and acids all differ because of their structure. This means that as well as water being produced, so is a salt.

Acid        +        Alkali                        Salt        +        Water

XH+        +        YOH¯                        XY        +        H20

HCl        +        NaOH                        NaCl        +        H20

Neutralisation is always an exothermic reaction, therefore heat is given out, because the energy released from forming bonds is greater then that taken in and used in the breaking of the bonds. The heat given off can be measured in each reaction by changing it into joules of energy. Heat of neutralisation is the heat change given form an acid and an alkali reacting together to form one mole of water.

Deciding on a method: Although there are many ways of investigating heat of neutralisation for this experiment I will only look at one. Methods that I could use include varying the volumes of both acid and alkali together or just one. I could also vary both of the concentrations, or just one of them. For the experiment I will vary both of the concentrations, as this is the most accurate method of doing it. I will look at the different temperature changes that occur with the different concentrations and at the heat of neutralisation.

Prediction: I predict that as the concentration of the alkalis and acids are increased, the temperature change will do so also. As neutralisation is an exothermic reaction the heat given off will increase or decrease in direct proportion to the number of ions present in the solution to react. Therefore, I predict that the most concentrated acid will react with the most concentrated alkali to give the greatest temperature change, a weak acid and a strong alkali, or vice versa, will give off a lesser temperature change, but a weak acid and alkali will give off the smallest temperature change.

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Energy change will rise in proportion to the concentration as well. However, energy per mole will not rise. One mole of a solution is varied in different solutions, consequently the concentration will affect the amount of solution involved in making a mole of water, but not the energy in a mole.


  • 500ml beaker
  • Two 50cm³ measuring cylinders
  • Two conical flasks
  • Thermometer
  • Two pipettes
  • Distilled water
  • Polystyrene cup, with lid
  • Labels, so that chemicals do not get mixed
  • Acid- strong Hydrochloric, weak Ethanoic and Propanoic
  • Alkalis- strong Sodium hydroxide, weak Ammonia solution

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