Lab: Titration Objectives • Understand the titration process • Use titration in a laboratory process to determine the acidity level of a solution • Demonstrate proper laboratory titration techniques when working with acids and bases Introduction The acid/base titration process relies on the use of a known concentration of a base (or an acid) to determine the unknown concentration of an acid (or base). Titration is based upon the neutralization reaction that occurs between acids and bases. Neutralization occurs when the equivalence point of the titration has been achieved. To determine when the neutralization takes place, a chemical, known as a neutralization indicator, is added to the solution. The neutralization indicator changes color when the desired pH is achieved. The acid-base indicator changes color at the end point of the titration – the point at which the pH level of the solution is determined. At the equivalence point, the number of H+ ions donated by the acid is equivalent to the number of H+ ions accepted by the base. © KC Distance Learning You can also use the titration process to calculate the quantity of moles of acid in a solution. Use the following equation to perform the calculation: molesacid = a = reaction coefficient of the acid Mb = molarity of the basic solution a x Mb x Vb b Vb = volume of base used in titration – converted to Liters b = reaction coefficient of the base Balance the reaction in order to determine the reaction coefficients of the acid and base. Once balanced, calculate the number of moles of acid in the solution. In this experiment, you will accurately determine the concentration of a solution of sodium hydroxide (NaOH) using a 0.500-M potassium hydrogen phthalate (KHP) standard solution. Add the acid-base indicator phenolphthalein, in its (colorless) acidic form, to a precisely measured volume sample of KHP. Slowly add the base, NaOH, to the sample of KHP. Once all the KHP has reacted with the base, the first excess drop of NaOH will cause the indicator to convert to its basic (pink) form. Then you can calculate the exact concentration of the NaOH solution. © KC Distance Learning Pre-lab Questions 1. How does the end point of a titration differ from the equivalence point? 2. How does a base differ from an acid? 3. Describe the term molarity as it relates to an acid or base. © KC Distance Learning Experiment: Titration In this experiment, you will be working with a simulated lab. Study the screen shot of the simulator and pay close attention to the highlighted controls. These controls, along with others specified in the lab procedures, will assist you in successfully completing this experiment. As you conduct each portion of the experiment, be sure to write down your observations. NOTE: If your experiment gets out of control, you can start over by clicking the reset button located on the right control panel. Materials © KC Distance Learning Procedure 1. Retrieve the KHP, 1M NaOH solution, and the phenolphthalein from the stockroom. • Double-click the Solutions cabinet to display the list of solutions. Double-click each solution to place it on the workbench. Note the volume of KHP, which can be found in the Solution Info window. 2. Retrieve a disposable pipette and a 50 mL burette. • Click the glassware button on the action bar. Click the necessary glassware that appears on the drop-down menu. 3. Use a disposable pipette to add a small amount (~0.3 mL) of indicator to the KHP solution. 4. Drag the pipette onto the indicator solution so the mouse pointer is inside the edges of the source container (the pipette). 5. When the pipette is above the indicator solution, briefly click the Withdraw button on the transfer bar. 6. Drag the pipette onto the KHP solution so that the mouse pointer is within the edges of the flask, and then briefly click the Pour button on the transfer bar. 7. Fill the burette with NaOH solution. 8. In the same manner as Step 4, drag the flask of NaOH onto the burette so the mouse pointer is inside the edges of the recipient container (the burette). 9. When the flask is tilted above the burette, click and hold down the Pour button in the transfer bar. 10. When you release the mouse button, the Solution Info window will allow you to infer how much has been transferred. 11. Titrate small volumes (~ 0.5 mL or less) of NaOH from the burette into the KHP until a slight color change occurs. Note the volume of NaOH used, which can be found in the Solution Info window. • The end point occurs when you see a slight pink color appear in the indicator solution. If the indicator solution turns red, you have passed the end point and will need to start over. © KC Distance Learning Post-lab Questions 1. What amount of NaOH was added to the indicator to reach the end point of the titration? 2. What would happen if you forgot to use the phenolphthalein indicator? 3. Rearrange the titration calculation to find the Mb in a solution. © KC Distance Learning
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