HONORS CHEMISTRY Acid-Base Titration L-16

INTRODUCTION

Titration is a process used to determine the volume of a solution of unknown concentration of base that will react with a carefully measured volume of known concentration of acid. It is a quantitative technique based upon the mole relationship of proton and hydroxide ions and is also called volumetric analysis. Since the # moles of acid =#moles of base, MAVA =MBVB. In this lab the indicator is added to show the end of the reaction by a color change.

MATERIALS

125 mL Erlenmeyer flask

two 50mL burets ($20 each)

buret clamp, pole, divider

50 mL beaker A (known acid)

100 mL beaker B (unknown base)

wash bottle (deionized water only)

phenolphthalein (1/table)

marking pencil (1/table)

white board (contrast)

PROCEDURE

  1. Clean and dry a 50mL and 100mL beaker. Rinse the Erlenmeyer flask with tap water. Label the beakers A and B. Check for leaky burets. These are brand new so I expect no problems.
  2. NEVER PULL ON THE BURET TIPS.
  3. Prepare burets for titration. Get about 50mL acid from table in your beaker. Add a few mL of acid to buret A and swirl. Toss the solution out in your sink and repeat. Now fill the buret with acid till almost the 0.00mL mark.
  4. Repeat step 2 with the second buret marked B with base solution from 100mL beaker.
  5. If your burets already contain solutions you need not rinse them. Just continue to replenish both solutions as needed.
  6. Read both volumes to the nearest 0.01mL mark and record in data table.
  7. From buret A deliver about 10 mL of acid into flask.
  8. Add 3 drops of phenolphthalein to the flask.
  9. Place the flask on the white board and under the buret B and start adding base in small amounts till the solution is a PALE PINK COLOR that lasts for 15 seconds. Use the wash bottle to wash any drops sticking to the tip of the buret. THE TIP MUST NOT TOUCH ANY PART OF THE FLASK OR THE SOLUTION!!!
  10. Make sure you don’t switch burets. If you over-titrate and the color is a bright pink, take your flask to the acid buret and add a few drops till desired color is achieved.
  11. Read both readings in the burets and record. The difference between initial and final readings will give you volume of acid and base solutions used.
  12. Discard the solution in flask, rinse first with tap water and then with deionized water .Repeat steps 5-9.
  13. Repeat for a third trial if necessary. You will need no more than three and no less than two trials.
  14. All calculations must be finished in the allocated time of 60 minutes.
  15. LAB REPORTS are due the day of the lab. So come prepared to work hard and manage your time. This lab is almost like a test so no talking to other groups. Points will be taken off if you do not follow the rules.
  16. NO CHANGING VOLUMES IN THE DATA TABLE ONCE RECORDED.SO MAKE SURE BEFORE YOU WRITE VALUES DOWN.
  17. Calculations must be shown in the box as shown. This lab is worth 60 points, 50 for accuracy.

ANALYSIS

Prepare a data table as follows.

TRIAL 1 / TRIAL 2 / TRIAL 3
INITIAL BURET READING ACID mL
FINAL BURET READING ACID mL
VOLUME OF ACID mL (VA)
INITIAL BURET READING BASE mL
FINAL BURET READING BASE mL
VOLUME OF BASE ADDED mL (VB)
MOLARITY OF ACID (MA)
MOLARITY OF BASE (MB)
AVERAGE MOLARITY OF BASE (MB)
Calculations for trial 1 / Calculations for trial 2
Calculations for trial 3 / Calculations for average molarity