What is pH? - PASCO



What is pH? Driving QuestionWhat does it mean when you measure pH? Materials and EquipmentpH Sensor 0.1 M HClTest tubes, 20 mm x 150 mm (5)0.1 M NaOH Test Tube rackUniversal indicatorGraduated cylinder, 10-mL Distilled water in a wash bottleGraduated cylinder, 50-mL (2)PipettesMarkersStirring rodpH buffers (4 and 10)Waste beakerBackgroundThe pH scale is associated with acids and bases. SafetyFollow these important safety precautions in addition to your regular classroom procedures:Wear safety goggles at all times! Use caution with acids and bases. Procedure - Acids1.Open the What is pH? lab file from the experiments menu in SPARKvue under High School>Chemistry.2.Connect the pH sensor.3.Calibrate the pH sensor with 4 and 10 buffers. 4.Label 5 test tubes with numbers #1- #5 and place them in the test tube rack.5. Pour about ~10 mL of 0.1 M HCl into the test tube labeled #1. Set this aside in the test tube rack.6. Make Mixture #2: Add 9 mL of distilled water to a 10-mL graduated cylinder.Use a pipet to add 1 mL of 0.1 M HCl to the same graduated cylinder and mix well. This is mixture #2.Pour mixture #2 into the test tube labeled #2. Set this aside in the test tube rack.7. You mixed 1 mL of 0.1 M HCl and 9 mL of water to make a total solution of 10 mL. What is the molarity of HCl in mixture #2? Enter this value in Table 1. 8.Make Mixture #3: Rinse the 10-mL graduated cylinder with distilled water then fill to the 9 mL mark with distilled water.Use a pipet to add 1 mL of mixture #2 to the graduated cylinder and mix well. This is mixture #3.Pour mixture #3 into the test tube labeled #3. Set this aside in the test tube rack.9.What is the molarity of HCl in mixture #3? Enter this value in Table 1.10.Make mixtures #4 and #5 by repeating Step 8. To make each solution, add 1 mL of the previous numbered solution to 9 mL of distilled water making a total volume of 10 mL. 11.What are the molarities of HCl in mixtures #4 and #5? Enter these values in Table 1. 12. Add a few drops of Universal indicator to each of the test tubes and mix well. Record the color of each test tube in Table 1. 13. Measure the pH of the mixture in each of the test tubes with the pH sensor. Be sure to rinse and dry the pH sensor between samples. Record the pH values in Table 1. Analysis - AcidsTable 1: Acid molarity and pH Molarity of HCl (M)Molarity of HCl in scientific notation (M)[H+](M)Value of the exponent of the [H+]Negative value of the exponent of the [H+]Color of solution with indicatorpH10.1023451.For each of the test tubes, express the Molarity of HCl in scientific notation. Record these values in Table 1. 2. HCl is a strong acid, meaning it completely dissociates in water to produce H+ and Cl-. The molar concentration of H+ is symbolized as [H+]. For each of the test tubes, write the [H+] in scientific notation in Table 1. 3. For each of the test tubes, record the value of the exponent of the [H+] in Table 1.4. For each of the test tubes, record the negative value of the exponent of the [H+] in Table 1.Questions - Acids1.What happened to the indicator as it was added to the test tubes. What do you think the indicator detects? 2. Would an indicator or a pH sensor be more useful if you needed an exact measurement of the pH of a solution. Explain. 3. pH is defined as the –log[H+]. Calculate the pH for each of the test tubes. What column of data in Table 1 does this match? 4. How do the calculated pH values compare to the measured pH values? What are some sources of error? 5. If your solution was 2 x 10-5 M H+, what is the approximate pH based on the exponent? Using your calculator, what is the actual pH? Procedure - Bases1.Clean and rinse the test tubes and graduated cylinders Label the 5 test tubes with numbers #9- #13 and place them in the test tube rack.2. Pour about ~10 mL of 0.1 M NaOH into the test tube labeled #13. Set this aside in the test tube rack.3. Make Mixture #12: Add 9 mL of distilled water to a 10-mL graduated cylinder.Use a pipet to add 1 mL of 0.1 M NaOH to the same graduated cylinder and mix well. This is mixture #12Pour mixture #12 into the test tube labeled #12. Set this aside in the test tube rack.4. You mixed 1 mL of 0.1 M NaOH and 9 mL of water to make a total solution of 10 mL. What is the molarity of NaOH in mixture #12? Enter this value in Table 2. 5.Make Mixture #11: Rinse the 10-mL graduated cylinder with distilled water then fill to the 9 mL mark with distilled water.Use a pipet to add 1 mL of mixture #12 to the graduated cylinder and mix well. This is mixture #11.Pour mixture #11 into the test tube labeled #11. Set this aside in the test tube rack.6.What is the molarity of NaOH in mixture #11? Enter this value in Table 2.7.Make mixtures #10 and #9 by repeating Step 5. To make each solution, add 1 mL of the previous numbered solution to 9 mL of distilled water making a total volume of 10 mL. 8.What are the molarities of NaOH in mixtures #10 and #9? Enter these values in Table 2. 9. Add a few drops of Universal indicator to each of the test tubes and mix well. Record the color of each test tube in Table 2. 10. Measure the pH of the mixture in each of the test tubes with the pH sensor. Be sure to rinse and dry the pH sensor between samples. Record the pH values in Table 2. Analysis - BasesTable 2: Acid molarity and pH Test tube #Molarity of NaOH (M)Molarity of NaOH in scientific notation (M)[OH-](M)Value of the exponent of the [OH-]Negative value of the exponent of the [OH-]Color of solution with indicatorpH130.1012111091.For each of the test tubes, express the Molarity of NaOH in scientific notation. Record these values in Table 2. 2. NaOH is a strong base, meaning it completely dissociates in water to produce Na+ and OH-. The molar concentration of OH- is symbolized as [OH-]. For each of the test tubes, write the [OH-] in scientific notation in Table 2. 3. For each of the test tubes, record the value of the exponent of the [OH-] in Table 2.4. For each of the test tubes, record the negative value of the exponent of the [OH-] in Table 2.Questions - Bases1.What happened to the indicator as it was added to the test tubes. What do you think the indicator detects? 2. pOH is defined as the –log[OH-]. Calculate the pOH for each of the test tubes. What column of data table 2 does this represent. 3. pOH is related to pH through the following equation:14 = pH + pOH What is the expected pH values for each of your test tubes? 4. How does the expected pH values for your trial compare to the measured pH values? 5. If your solution was 2 x 10-5 M OH-, what is the value of the pOH and the value of the pH? ................
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