For this experiment, Hydrochloric Acid and Sodium Hydroxide is going to be used. When these two chemicals are mixed, common salt is formed.
Hydrochloric Acid contains free hydrogen ions (H+) in an aqueous solution. Sodium Hydroxide has free hydroxide ions (OH-) in solution. When neutralization occurs, the opposite charges are attracted to one another to form water.
H+ (a) + OH- (a) → H2O (l)
The formula for Hydrochloric Acid and Sodium Hydroxide is:
Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water
HCl + NaOH → NaCl + H2O
To change the concentration of a chemical from 1 mol dm-3 to 0.1 mol dm-3, put 1 ml of the acid or alkali on a measuring cylinder and mix it with 9 ml of water. To make the concentration 0.2 mol dm-3, add 2 ml of acid or alkali and 8 ml of water and so on.
Some examples of neutralisation in everyday life are:
Indigestion – when there is too much acid in the stomach, it can be neutralised by an alkaline tablet often containing aluminium hydroxide.
Bee sting – this is acidic. It can be neutralised by a bicarbonate of soda to counter the excess acid.
Wasp sting – this is alkaline. Vinegar can be used for neutralisation.
Power stations use lime or limestone to neutralisation gas before it leaves the chimneys. This process makes calcium sulphate which can be sold to make plaster.
Prediction
I predict that as the concentration of the acid and alkali in increased, the temperature will also increase when neutralisation occurs. This is because neutralisation reactions are also exothermic reactions. They will be giving out heat energy.
Method
Set up equipment (see diagram below). Measure 0.1 mol dm-3 of both Hydrochloric Acid and Sodium Hydroxide and put them on separate measuring cylinders. To make measuring easier, use three burettes – one for the Hydrochloric Acid, one for the Sodium Hydroxide and one for the water. Mix them together onto a test tube and record the temperature. Repeat the experiment for 0.2 mol dm-3 of Hydrochloric Acid and Sodium Hydroxide up to a concentration of 1 mol dm-3.
The input variables in the experiment are:
- The concentration of the acid.
- The concentration of the alkali.
The output variables are:
- The change in temperature.
The constants are:
- The starting temperatures of the acid.
- The starting temperatures of the alkali.
- The volume of acid and alkali.
Safety
For safety, these rules should be followed:
- Wear safety goggles at all times.
- Make sure there is good ventilation as some solutions have strong smells.
- Sodium Hydroxide is corrosive and Hydrochloric Acid is irritant so wash your hands thoroughly if there is any contact with the chemicals.
- Thermometers contain mercury which is poisonous so be careful not to break it.
- Handle all glassware with care as they may be hot after a reaction takes place.
Fair Test
These are the regulations that should be followed in order for a fair test:
- Make sure the same volume is used every time.
- Wait until the temperature has reached its maximum for the reaction before recording it. The best way to know this is when it is starting to drop.
- Hold the conical flask at the top to avoid the contents getting hot by body heat.
- Repeat each experiment three times to show up any anomalous results.
Equipment
Hydrochloric Acid
Sodium Hydroxide
Beaker
Test tube
Measuring cylinder
Burette
Thermometer
Diagram
Results
The experiment was carried out at room temperature (22OC).
Conclusion
From my graph I can see there is a strong positive correlation. The temperature increases by about 0.5OC each time the concentration is increased by 0.1 mol dm-3. An anomaly was when the concentration was 0.9 mol dm-3, the average temperature did not increase.
Evaluation
The experiment is successful as a pattern could be seen from the graph. The equipment was washed every time to ensure there were no solutions left. The same volume of chemicals was put in each time.
If a digital thermometer was used, the temperatures could be more accurate.
If I had used a wider range of concentrations for the acid and alkali – such as 0.5, 1, 1.5 and 2 mol dm-3, I would have got bigger differences for the concentrations. On my experiment, the concentrations go up by 0.1 mol dm-3 every time and therefore, there aren’t any big differences in the results.
If I had more time to do my experiment, I would have made this change. To make the experiment better, I will use a bigger scale next time.
