Investigate the effect that concentration has on a reaction on these factors: Temperature rise, Heat evolved, and Heat given off due to the neutralization between Hydrochloric Acid and Sodium hydroxide solution.

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13. 03. 04


Aim- to investigate the effect that concentration has on a reaction on these factors:

  • Temperature rise
  • Heat evolved
  • Heat given off due to the neutralization between Hydrochloric Acid and Sodium hydroxide solution.

Neutralization takes place when acids react with substances called bases. When they react their acidity is cancelled out, and the reaction always produces a salt and water. The base can be soluble (when called an alkali) or insoluble like copper (II) oxide.

Neutralization can be used for:

  • Treating insect bites (that are acidic)
  • Making fertilizers and other salts in industry.
  • Reducing the acidity in soil, to make it better for plants to grow and live in it.

The heat of neutralization is the heat change when 1 mole of the acid used is neutralized. That is, it is the heat given out when water molecules are produced from one mole of acid.

Following is the ionic equation that is stated for the neutralization reaction that we will carry out in the lab.

NaOH(aq) + HCL(aq) ——―> NaCL(aq) +H2O(l)

Na+ + OH- + H+ + CL- ——―> Na+ + CL- + H2O

H+(aq) + OH-(aq) ——―> H2O(l)

Hence, Na+(aq) + CL-(aq) ——―> NaCL(s)

When the hydrochloric acid is mixed into the sodium hydroxide solution, the ions react with the various other ions present in the solution.

In this increased (in volume) solution, the spectator ions are Na+ and CL-, as the ions of H+ and OH- react to form H2O. These spectator ions (Na+ and CL-) do not react to form a salt until the Water is formed from the H+ and OH- ions.

In this reaction all four ions present, form bonds between each other, hence a lot of energy is given out. The reaction is said to given out a lot of energy, and hence reactions that give out energy are called exothermic. It is exothermic as there is no bond breaking in the reaction. If we observe the reaction, all ions form bonds between themselves and there are no breakage of bonds between any atoms. If the energy taken in is less than the energy given out when new bonds form, the reaction is exothermic. A lot of heat gets evolved from this reaction and the temperature rises. This heat evolved is due to the fact that bonds are made between the four ions.

Although there seems to be an overall bond-making reaction, there is also a slight bond breaking process taking place in the reaction, as the ionic compound, Sodium chloride that is formed is soluble in water. Water is a polar solvent and is able to separate the positive (Na+) ions and negative (CL-) ions. Hence the ionic compound partially dissolves in the water, which is also formed in the reaction.

There are two structures that we can perceive of a water molecule:

Shape 1, which is the H-O-H


Shape 2, which is               O                 

                         H                    H

We take the structure of shape two to be correct as we say that the two types of ions involved in the covalent bond are of different charges. So the positive H+ ions repel the negative O2- ion hence forming the triangular structure for the bond.

Water molecule:

Next I will carry out the investigation of doubling and tripling the concentrations and verifying its effects that it has on, the temperature, heat of neutralization and heat evolved.

                  H+                       OH-                                   Na+


            Cl-                                             Na+                                          Cl-


   25 cm3 of 1M HCl       25 cm3 of 1M NaOH            50 cm3 of NaCl solution

          H+    Cl-                        OH-     Na+                       Na+             Cl-

                                                                                             H2O                    H2O

          Cl-       H+                 Na+     OH-                        Cl-                Na+


   25 cm3 of 2M HCl       25 cm3 of 2M NaOH            50 cm3 of NaCl solution

In the diagrams we see that as the as the concentration of the solution doubles, the number of H+ ion and OH- ions also double and as a result temperature and heat evolved doubles and heat of neutralization stays the same.

For the actual experiment I am planning to use four different concentrations to investigate their affects, these are 0.8M, 1.2M, 1.6M and 2.0M


List of Apparatus:

  • 2 Burettes
  • Clamp stand
  • Plastic cup
  • Thermometer
  • 2 conical flasks
  • Pen and paper

Materials used:

  • Sodium hydroxide solution
  • Hydrochloric Acid
  • Tissue paper

The way in which I will conduct the experiment:

First I will have two burettes to accurately measure out the right amounts of hydrochloric acid in one of them and sodium hydroxide in the other. After measuring them, I will first put 20cm3 of the alkali into a plastic cup and then move the cup under the burette containing the 40cm3 of acid. We insert the thermometer into this mixture of acid and alkali and then measure the temperature, as the neutralization is taking place. The process consists of letting 5cm3 of acid go off into the cup at certain intervals, hence at each time noting down the temperature change value. This will be repeated until all 20cm3 of the acid has been added:

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Alkali burette           Acid burette adding 5cm3 at intervals. Solution gradually becomes colourless.



After this a graph showing the temperature and the volume of acid will have to be plotted:





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