Acid Strengths. Evaluation copy. ring stand and utility clamp. H 3 BO 3, boric acid. 5 small test tubes HCl, hydrochloric acid test tube rack

Transcription

1 Acid Strengths Computer 18 Acids react with metals. For example, hydrochloric acid reacts with zinc metal according to the equation Zn(s) + 2 HCl(aq) H 2 (g) + ZnCl 2 (aq) Strong acids react faster and more vigorously with metals than do weak acids. Because water solutions of acids contain ions, these solutions conduct electricity. The measure of electrical conductivity is related to the number of ions in solution. Conductivity units are microsiemens per centimeter (µs/cm). OBJECTIVES In this experiment, you will React zinc metal with various acids. Use a computer to measure electrical conductivity. Investigate the relationships among acid strength, electrical conductivity, degree of ionization, and chemical activity. MATERIALS computer sand paper Vernier computer interface 100 ml beaker Logger Pro distilled water Vernier Conductivity Probe HC 2 H 3 O 2, acetic acid ring stand and utility clamp H 3 BO 3, boric acid 5 small test tubes HCl, hydrochloric acid test tube rack H 3 PO 4, phosphoric acid 5 zinc metal strips rinse water (distilled water) Evaluation copy Figure 1 Physical Science with Vernier 18-1

2 Computer 18 PROCEDURE 1. Obtain and wear goggles! CAUTION: Handle the acids in this experiment with care. They can cause painful burns if they come in contact with your skin or get into your eyes. Part I Chemical Activity 2. Get 5 test tubes and label them 1 through Using the sequence (or order) in the data table, place 20 drops of the proper acid (or distilled water) into each of the test tubes. Use the dropper bottles supplied. 4. Use sandpaper to clean one end of each of 5 zinc strips. Place a zinc strip into each of the test tubes, with the cleaned end in the liquid. Record your observations in the Data and Observations Table. Compare the chemical activities of the different solutions. You will later be asked to rank the acids from most active to least active. Record observations that will help you make this activity ranking. 5. Remove the zinc strips from the test tubes. Rinse and dry the strips before returning them to their container. Dispose of the test tube contents as directed by the teacher. Wash the test tubes and return them to their container. Part II Conductivity 6. Attach the Conductivity Probe to the computer interface. It should be set on the µs/cm position. 7. Prepare the computer for data collection by opening the file 18 Acid Strengths from the Physical Science w Vernier folder. 8. Get one of the solutions and test it as follows: a. Carefully raise the container until the hole in the probe end is completely submerged in the solution. Swirl the solution briefly. b. Once the reading has stabilized, record the value. 9. Before testing the next solution, rinse the probe with distilled water. 10. Use the Step 8 procedure to test the other 4 solutions. Be sure to rinse the probe with distilled water between tests Physical Science with Vernier

3 Acid Strengths DATA AND OBSERVATIONS No. Solution Reaction with Zinc Conductivity 1 H 2 O µs/cm 2 HC 2 H 3 O 2 µs/cm 3 H 3 BO 3 µs/cm 4 HCl µs/cm 5 H 3 PO 4 µs/cm PROCESSING THE DATA 1. Using formulas, rank the 5 solutions first by activity and then by conductivity. Activity Conductivity 1 (highest) (lowest) 2. What is the relationship between chemical activity and conductivity? Explain why this relationship exists. (Hint: Use the word ion in your explanation.) 3. Name the strongest acid studied in this experiment. Explain how you made this choice. Physical Science with Vernier 18-3

4 Computer Name the weakest acid studied. Explain how you made this choice. 5. What do the terms strong and weak mean here? 6. The four acid solutions we used all had the same concentration. Why were their conductivities different? EXTENSIONS 1. Measure and study the conductivities of common laboratory acids, bases, and salts Physical Science with Vernier

5 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: Vernier Software & Technology S.W. Millikan Way Beaverton, OR Toll Free (888) (503) FAX (503)