In this experiment you will determine the heat of the neutralization reactions between sodium hydroxide and two acids: hydrochloric and sulfuric.
The neutralization reaction is the reaction
between the acid and a base that produces water and a salt ......not
the table salt, of course. This term is commonly used to describe an ionic
compound formed from an acid and a base, which contains a metal cation
or ammonium ion and an anion.
2NaOH(aq) + H2SO4 (aq) ----> Na2SO4
Base Acid Salt
The reaction between acid and a base produces
heat. Therefore, it is an example of an exothermic reaction.
You can calculate the heat of neutralization using the following equation:
DH= -(V x d x DT x Cp) Eq.2
V= volume of the reaction mixture, mL ( sum of the volumes of acid and base solutions)
d= density of the reaction mixture, g/mL
DT = temperature change (the maximum mixture temperature after mixing minus the initial temperature of the acid before the two solutions were mixed, oC)
Cp = heat capacity of the reaction mixture =
energy required to increase the temperature of 1 gram of the solution by 1oC.
For sodium hydroxide/sulfuric acid mixture: Cp =3.76 J/g oC; density =1.04 g/mL.
For sodium hydroxide/hydrochloric acid mixture: Cp= 3.89 J/g oC; density = 1.12 g/mL.
The heat absorbed by the Styrofoam cup (calorimeter) is negligible and does not have to be taken into account for the purpose of this lab.
Be extremely careful when working with 2.0 M solution of NaOH (sodium hydroxide) and HCl ( hydrochloric acid) as well as with 1.0 M solution of H2SO4 (sulfuric acid). All of these solutions are toxic and corrosive, and may cause permanent burns. Sulfuric acid is also an oxidizer! Use hood to dispense the solutions.
1. Prepare a ring stand with a small ring and a clamp. Obtain a 6 oz Styrofoam cup And a thermometer.Support the cup in a ring, but do not suspend the cup in the air- keep it on the table
2. Measure 20 ml of 1.0 M sulfuric acid in your 50 ml graduated cylinder and add the acid to the cuP. Secure a thermometer in a clamp and insert the thermometer in the acid, making sure that the thermometer tip does not touch the bottom or walls of the cup.
3. Let the temperature equilibrate for 5 minutes. During this time wash the graduated cylinder with water, dry it well with a paper towel, and measure 20 ML of the 2.0 M sodium hydroxide solution.
4. Record the temperature of the acid. Without removing the thermometer from the cup, add the sodium hydroxide solution to the acid, all at once. Gently Stir the solution with the thermometer . Record the temperature, starting 0.5 minute after the mixing, then in 1 minute intervals, for additional 5 minutes.
5 . REPEAT THE STEPS 1 THROUGH 4 USING 20 mL of 2.0 m HYDROCHLORIC ACID AND 20 mL of 2.0 MOLAR SODIUM HYDROXIDE.
1. Calculate the volume in mL of the final reaction mixture: V= V base + Vacid
2. Calculate T for each reaction : DT = Tmax - Tinitial acid
3. Use Eq. 2 to calculate the enthalpy of the neutralization reaction between the sulfuric acid and sodium hydroxide as well for the reaction between the hydrochloric acid and sodium hydroxide.
1.If you did not ignore the heat absorbed by a calorimeter, but somehow measured it and used in the calculations, would the calculated heat of reaction be lower or higher? Hint: will the heat absorbed by the calorimeter have to be added or subtracted from your calculated heat of reaction? Explain.
2. Glass conducts heat easily and is not
as good an insulator as styrofoam. If you performed the neutralization
reaction in a glass
beaker instead of a styrofoam cup, would you expect to register more or less heat released by the reaction ? Explain.
3. How can you tell whether the reaction
is exothermic or endothermic based on the temperature measurements of the
mixture before and after the reaction?
4. Does the heat of neutralization reaction
depend on the number of hydrogen atoms in a molecule of acid or not?
your experimental results.