Materials: Solid potassium hydrogen phthalate (KHP) Sodium hydroxide (NaOH) solu
ID: 593732 • Letter: M
Question
Materials: Solid potassium hydrogen phthalate (KHP) Sodium hydroxide (NaOH) solution Acetic acid (CH,COOH) solution Phenolphthalein indicator Distilled water 250 mL Erlenmeyer flask 25.0 mL volumetric pipette Pipette bulb Burette with stopcock Burette clamp Funnel Retort stand - Balance White paper - pH Meter - - - Part A-Standardization of NaOH Purpose: To calculate the exact concentration of the prepared solution of sodium hydroxide. In order to have accurate titration results we need to know the exact concentration of the sodium hydroxide we are titrating with. Procedure 1. Set up an observation table to record the initial and final volumes, of NaOH in your burette at the beginning and end of titration, volume used, as well as the mass of KHP for each trial. 2. Weigh approximately 1.00 g of potassium hydrogen phthalate (KHP - molecular formula KHC,H,O), and record the mass. Place the KHP into a clean Erlenmeyer flask. Add -50.0 mL of distilled water (enough to dissolve it) and two to three drops of phenolphthalein indicator. Swirl to mix the solution. 3. Carefully fill your burette with NaOH solution. Stop at the 5.0 mL line in order to not overfill the burette. Record the initial volume of NaOH in the burette. Remember to always record your volume at the bottom of the meniscus. 4. Place the Erlenmeyer flask over a sheet of white paper and slowly begin titrating with the NaOH solution. Be sure to add NaOH in slow increments to improve accuracy. Mix your solution during titration by swirling the flask. At the first sign of color change close the stopcock on your burette. From this point forward only 5. add one drop of NaOH at a time. Swirl to mix after each drop and watch for color change. 6. When the solution changes color permanently record the final volume of NaOH in the burette 7. Repeat steps 1-5 (complete at least three trials).Explanation / Answer
KHP is used a a primary standard for titration with NaOH.
A primary standard such as KHP is a solid which is not moisture sensitive or air sensitive. It is stable under normal conditions. It can be weighed accurately so the solution can be prepared well with absolute concentration.The solution once prepared also remains stable without any change in concentration over time. It reacts in a 1 : 1 molar ratio with base NaOH. These properties of KHP makes it an ideal candidature for titration with NaOH for standadrizing NaOH solution.