Chemistry 122 Heat of an Acid – Base Chemical Reaction 1
Purpose:
· To measure the amount of heat involved in an acid – base chemical reaction.
INTRODUCTION:
The foundation of the study of thermochemistry was laid by the chemist Germain Hess, who investigated heat in chemical reactions during the last century. One statement of the law that bears Hess's name says:
The enthalpy change for any reaction depends on the products and reactants and is independent of the pathway or the number of steps between the reactant and product.
In this experiment, you will measure the quantity of heat involved in an acid base reaction. The heat of reaction will be measured using a styrofoam calorimeter. The is shown below:
Reaction : The reaction of sodium hydroxide solution with dilute hydrochloric acid solution.
Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) + heat
APPARATUS AND MATERIALS:safety goggles / 150 mL styrofoam cup / thermometers
100 mL graduated cylinder / 0.500 mole NaOH(aq)
L / 0.500 mole HCl(aq)
L
SAFETY:
· Hydrochloric acid and sodium hydroxide are corrosive. Avoid direct contact. If any touches your skin, wash it off immediately.
PROCEDURE:
The Reaction of Sodium Hydroxide Solution with Hydrochloric Acid Solution
1. Accurately measure 75.0mL of 0.500 mol/L hydrochloric acid solution, using a 100 mL graduated cylinder. Pour the HCl solution into the styrofoam cup. Use another 100 mL graduated cylinder to measure 75.0 mL of 0.500 mol/L sodium hydroxide solution.
2. Record the temperature of the HCl solution in the calorimeter. Both solutions are at room temperature, so both have the same initial temperature.
3. Add the sodium hydroxide solution from the cylinder to the acid solution in the styrofoam cup. Stir the mixture with the thermometer and record the highest temperature reached (to the nearest 0.1oC).
4. Discard the solution by pouring it down the drain. Rinse the cup and graduated cylinders thoroughly.
CALCULATIONS:
1. Identify the system and surroundings.
2. Calculate the energy change of the surroundings.
3. Calculate the energy change of the system.
4. Use the volume of solution and Molarity to calculate the number of moles of NaOH and HCl.
5. Calculate the molar heat of reaction for this neutralization reaction.
QUESTIONS:
1. Use the molar heat of reaction to calculate the energy change for 60.0 grams of NaOH (assume sufficient HCl present for the reaction).
2. Calculate the mass of NaOH that would be needed to react with a sufficient supply of HCl to produce 50kJ of energy.