Effect of concentration of the acid&alkali on heat of neutralization

Thus, we chose the first question, that is, if the concentration of the acid and base reacting would affect the heat of neutralization. We chose HCl to be the acid and NaOH to be the base as they are a strong acid and base respectively, and also, since the chemical equation of the reaction is:

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

They require an equal volume in order to neutralize each other given that the concentration is the same.

Our hypothesis is thus: A higher concentration of the acid and base would produce a higher heat during the reaction

Also, the variables present in our experiment would be:

Independent Variable: Concentration of HCl and NaOH

Dependent Variable: Amount of heat produced by the reaction

Controlled Variable: Volume of the HCl and NaOH mixed together

Our rationale of investigation to observe a trend in the relationship between the concentration of acid and base, and the amount of heat produced as a result of the reaction. From this information, we can also deduce the molar heat of neutralization of HCl by NaOH. One possible application of this experiment is to help people who eat antacids. When the base in the antacid neutralizes the acid in our stomach, heat will be produced and the patient will feel heaty. However, if we can find out the molar heat of neutralization, we can advise the patient to drink a certain amount of water to keep their temperature low.

MATERIALS AND METHODOLOGY

The materials used were the following below:

1. 50ml of each 2.0mol HCl, 2.0mol NaOH
2. 50ml of each 1.0mol HCl, 1.0mol NaOH
3. 50ml of each 0.5mol HCl, 0.5mol NaOH
4. 50ml of each 0.2mol HCl, 0.2mol NaOH.
5. Thermometer
6. 2 Measuring Cylinders
7. 1 Beaker

Method

1. Measure 50ml of each 2.0mol HCl and NaOH using the 2 Measuring Cylinders.
2. Pour 50ml of 2.0mol NaOH from the measuring cylinder into the beaker.
3. Measure the initial temperature of the liquid using the thermometer.
4. Pour 50ml of 2.0mol HCl into the beaker containing NaOH. Make sure that all of the liquid is poured in as quickly as possible.
5. Measure and record the highest temperature reached, and this would be the final temperature
6. Repeat steps 1-6 above using concentrations of 1.0mol, 0.5mol and 0.2mol.
7. Subtract the initial temperature from the final temperature to get the change in temperature.

RESULTS

From this, we can see that higher concentrations of the acid and base will produce a greater amount of heat when they react together.

Also, to calculate the molar heat of neutralization, we are given the equation:

In which Q is the amount of energy produced, m is the mass of the solution, c is the specific heat capacity of the solution, and ∆T is the change in temperature of the solution.

We can also assume that the specific heat capacity and density of the solution to be similar to water, and thus, they would be 4.184J/g and 1.00g/ml respectively.

Total mass of water:

Approximate temperature change for the concentration of 1mol (derived from graph above):

And thus:

Also, we used 50ml of 1mol acid and base each. Therefore, the amount of mol of the acid or base will be:

Finally we get:

CONCLUSION AND DISCUSSION

Thus we can conclude that there is linear relationship between the concentration of the acid and base, and the change in temperature of the solution, and that a higher concentration of the acid and base would produce a greater amount of heat when they react together. We can see this as the 2.0mol acid and base caused the solution to rise 13°C in temperature, as compared to the 0.2 mol acid and base, which caused the solution to rise only 2°C in temperature. Finally, we conclude that the molar heat capacity of HCl by NaOH is approximately 52.5kJ/mol from the mathematical equation above.