Neutralization Reactions Computer 6 If an acid is added to a base, a chemical reaction called neutralization occurs. An example is the reaction between nitric acid, HNO 3, and the base potassium hydroxide, KOH. HNO 3 + KOH H 2 O + KNO 3 Neutralization produces a salt and water. KNO 3 is the salt in the above reaction. Heat energy is generally released, and the amount of heat released depends upon the properties of the acid and the base. Temperature measurements, made with a Temperature Probe, can be used to study the heat effects of neutralization. Acids and bases may be classified as weak or strong. These terms, weak and strong, have nothing to do with the concentration of the acid and base. The strength of an acid or base only refers to its ability to break up into ions in water. A strong acid or base breaks up completely into ions when added to water. A weak acid or base will not break up completely into ions when added to water. Much of the weak acid or base remains as molecules. Since the conductivity of a solution is determined by ion concentration in the solution, a Conductivity Probe can be used to determine the strengths of acids and bases. OBJECTIVES In this experiment, you will Use conductivity to determine the strengths of acids and bases. Use litmus paper to distinguish acids and bases. Use a computer to measure temperatures of reactants and products of neutralization reactions. Study the relationship between acid and base strength and heat released during neutralization. MATERIALS computer Styrofoam cup and 250 ml beaker Vernier computer interface red and blue litmus paper Logger Pro sodium hydroxide, NaOH, solution Vernier Temperature Probe hydrochloric acid, HCl, solution Vernier Conductivity Probe ammonium hydroxide, NH 4 OH, solution 50 ml graduated cylinder acetic acid, HC 2 H 3 O 2, solution Evaluation copy Figure 1 Physical Science with Vernier 6-1
Computer 6 PROCEDURE 1. Your teacher will use a Conductivity Probe connected to a computer to measure the conductivity of each solution. Record the results in the data table. 2. Obtain and wear goggles! CAUTION: Handle the acids and bases in this experiment with care. They can cause painful burns if they come in contact with your skin or get into your eyes. 3. Connect the Temperature Probe to the computer interface. Prepare the computer for data collection by opening the file 06 Neutralization from the Physical Science w Vernier folder. 4. Place a Styrofoam cup into a 250 ml beaker, as shown in Figure 1. Measure out 50 ml of NaOH solution into a 50 ml graduated cylinder. Pour the NaOH solution into the Styrofoam cup. 5. Use a stirring rod to transfer 1 drop of the NaOH solution to a piece of red litmus paper. Record the results. Repeat the procedure using blue litmus paper. 6. Place the Temperature Probe into the NaOH solution. 7. Rinse the 50 ml graduated cylinder with water. Then measure out 50 ml of HCl solution. 8. Use your stirring rod to test the HCl solution with red and blue litmus paper. Record the results. 9. Note: The Temperature Probe must be in the NaOH solution for at least 45 seconds before this step. Click to begin data collection. After a few seconds, add the HCl to the NaOH in the Styrofoam cup. Gently and continuously stir the solution. Collect data until a maximum temperature has been reached and the temperature readings are dropping, then click. 10. Click the Statistics button,. Record the minimum and maximum temperatures. 11. Dispose of the reaction products as directed by your teacher. 12. Repeat Steps 4 11, replacing NaOH with NH 4 OH and HCl with HC 2 H 3 O 2. 6-2 Physical Science with Vernier
Neutralization Reactions DATA AND OBSERVATIONS Solution Conductivity (µs/cm) Red litmus Blue litmus sodium hydroxide NaOH hydrochloric acid HCl ammonium hydroxide NH 4 OH acetic acid HC 2 H 3 O 2 NaOH + HCl NH 4 OH + HC 2 H 3 O 2 Minimum temperature C C Maximum temperature C C PROCESSING THE DATA 1. Calculate the temperature change, t, for each reaction. Subtract the minimum temperature from the maximum temperature. 2. Which neutralization reaction had the larger temperature change? 3. Were the two neutralization reactions endothermic or exothermic? Physical Science with Vernier 6-3
Computer 6 4. Write a balanced equation for the reaction between NaOH and HCl. You can use the model given in the experiment introduction. 5. Write a balanced equation for the reaction between NH 4 OH and HC 2 H 3 O 2. 6. One of the reactions studied involved a strong base and a strong acid and the other reaction involved a weak base and a weak acid. According to the conductivity values, which reaction involved a strong base and a strong acid? Explain. 7. From the results of this experiment, how is the amount of heat released in a neutralization reaction related to the strengths of the acid and base involved? EXTENSIONS 1. Repeat the experiment using other acids and bases and compare the results. 2. Try weak base and strong acid combinations and strong base and weak acid combinations. 6-4 Physical Science with Vernier
Vernier Lab Safety Instructions Disclaimer THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB. This copy does not include: Safety information Essential instructor background information Directions for preparing solutions Important tips for successfully doing these labs The complete Physical Science with Vernier lab manual includes 40 labs and essential teacher information. The full lab book is available for purchase at: http://www.vernier.com/cmat/psv.html Vernier Software & Technology 13979 S.W. Millikan Way Beaverton, OR 97005-2886 Toll Free (888) 837-6437 (503) 277-2299 FAX (503) 277-2440 info@vernier.com www.vernier.com