Experiment 7, Analysis of KHP by titration with NaOH Wright College, Department of Physical Science and Engineering

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1 Name Date Experiment 7, Analysis of KHP by titration with NaOH Wright College, Department of Physical Science and Engineering In this experiment, you will determine the amount (percent) of potassium hydrogen phthalate (KHP) that is in an impure sample. You will determine the percent of KHP via titration using NaOH with known molarity. The reaction will follow, KHC 8 H 4 O 4 (aq) + NaOH (aq) > KNaC 8 H 4 O 4 (aq) + H 2 O (l) At the end point, the moles of KHP will equal the moles of NaOH. You will use phenolphthalein as the indicator. The end point of the reaction will be a light pink solution color. PRELAB ASSIGNMENT 1. How will you know the reaction is over? 2. About how much KHP will be used in the titration? 3. Which 3 substances go into the 250 ml Erlenmeyer flask for the titration? 4. What is the mole to mole ratio in the reaction of KHP and NaOH? 5. What solution goes into the buret? PROCEDURE All waste can be put down the sink. 1. Record the KHP unknown number and the concentration of the NaOH solution in the report sheet. 2. Boil about 400 ml of deionized H2O for about 5 minutes and let cool. This procedure will remove any dissolve carbon dioxide that is naturally found in water. Carbon dioxide in water produces carbonic acid (H2CO3), an unwanted acid. 1

2 3. Using weighing paper, weigh a sample of your impure KHP that is between 1.00 grams and 1.20 grams and record the exact mass. 4. Add the KHP to a 250 ml Erlenmeyer flask along with 100 ml of deionized H2O and 2 drops of phenolphthalein indicator. Use your glass stirring rod to completely dissolve the KHP. 5. Obtain about 200 ml of NaOH solution. Use about 25 ml of the NaOH solution to rinse out a buret. Don t forget to release some of the NaOH solution out the bottom of the buret. This is waste, put it down the sink. 6. Fill your buret up close to the zero line with the NaOH solution and record the initial volume in the report sheet. Remember to read the buret to 0.01 ml. 7. Move the 250 ml Erlenmeyer flask containing the KHP solution and indicator under the buret and begin to add (titrate) the NaOH. Swirl the Erlenmeyer flask with one hand and operate the buret s stopcock with your other hand. When you see the pink color persisting, slow the titration down by adding smaller increments of NaOH. Keep swirling the solution. Remember to stop at the end point the LIGHT pink color. 8. Once the solution is light pink, and stays pink, stop and read the buret to 0.01 ml for the final volume of NaOH. Record the final volume of NaOH in the report sheet. Calculate the volume of NaOH used in the titration by subtracting the initial volume from the final volume of NaOH and record it in the report sheet. 9. Convert the ml of NaOH to L of NaOH. Show your calculation below. 10. Convert the L of NaOH to moles NaOH using the molarity of the NaOH solution. Show your calculation below and record the moles of NaOH in the report sheet. 11. Use the balanced chemical equation to convert moles of NaOH to moles of KHP (KHC8H4O4) Record the moles of KHP in the report sheet. Show your calculation here. 2

3 12. Calculate the molar mass of KHP (KHC8H4O4) and use it to convert the moles of KHP to grams of actual KHP in the sample you weighed out. Show your calculation below and record this mass in the report sheet. 13. Calculate the percent of KHP in your unknown sample by dividing the actual mass of KHP by the mass of the impure KHP and multiplying by 100. Show your calculation below and record this mass in the report sheet. 14. Repeat the titration and record the data 2 more times for Trial 2 and 3. Calculate an average percent KHP for your 3 trials. 3

4 KHP Titration Report Sheet KHP unknown number Concentration of NaOH solution M Trial 1 Trial 2 Trial 3 Mass of impure KHP g g g Initial NaOH volume ml ml ml Final NaOH volume ml ml ml NaOH volume used for titration ml ml ml NaOH volume used for titration L L L Moles of NaOH used for titration mol mol mol Moles of KHP in sample mol mol mol Grams of KHP in sample g g g Percent KHP in sample % % % Average percent KHP in samples % 4

5 QUESTIONS (Show your work) In a titration experiment, M KOH is added from a buret to 27.4 ml of a M H2SO4 solution and reacts according to the equation: 2 KOH (aq) + H2SO4 (aq) > K2SO4 (aq) + 2 H2O (aq) How many milliliters of potassium hydroxide solution have been added at the equivalence point (end point)? 2. In a titration experiment, M NaOH is added from a buret to 31.2 ml of a M H3PO4 solution and reacts according to the equation: 3 NaOH (aq) + H3PO4 (aq) > Na3PO4 (aq) + 3 H2O (aq) How many milliliters of sodium hydroxide solution have been added at the equivalence point (end point)? Updated MV 5