Experiment: Acid – Base Titration

Purpose: To completely neutralize a solution of  HCL with a prepared NaOH solution using a series of titrations.

Materials:

• Buret

• Pipette

• Pipette filler

• Erlemeyer flask

• funnel

• stand

• watch glass

• electronic balance

• 250.0 ml volumetric flask

• sodium hydroxide pellets

• 0.2500 M HCl

• phenolpthalein indicator

• distilled water

Procedure

PART A. Preparing the sodium hydroxide solution.

1. Place a watch glass on the electronic balance (under the hood) and tare it out.

3. Using a spatula, add  3 pellets of solid sodium hydroxide.  Record the mass extremely accurately on your data table. (NOTE: DO THIS STEP QUICKLY because the NaOH is hygroscopic and will absorb water from the air and mess up the mass.)

4. Using great care, transfer the entire solid to the volumetric flask.

5. Add approximately 100.0 mL of distilled water to the solid in the volumetric flask, replace the stopper and swirl the flask to dissolve the solid.

6. When the entire solid has dissolved, fill up to the mark taking great care when approaching the line. Near the mark add distilled water drop by drop using a pipette.

7. Calculate the exact concentration of the solution you have prepared.   Remember that concentration is molarity which is M = #grams / formula weight / 1 L solution.

PART B. Performing the titration.

1. Pipette exactly 25.00 mL of the HCl solution into an Erlenmeyer flask.

2. Add a few drops of phenolpthalein indicator. The solution should remain clear (Remember: Phynolphthalein is clear in acid and turns pink in bases).

3. With the aid of a funnel, carefully fill the buret with NaOH, noting the initial reading.  NOTE: As long as you know the beginning volume and the ending volume, you do NOT need to start each titration at a 0.00 mL!  

LAB TECHNIQUE HINT:    You need to first remove any air that is trapped at the bottom of the buret at the tip (below the stopcock) or otherwise, you will get improper volume readings.  

• After you have filled the buret with the NaOH solution, place an empty beaker underneath the buret tip.  

• Carefully open the stopcock and let enough solution come out of the tip so that all air is removed.  

• THEN (and only then) make your "initial" volume reading before you start the titration.  Record the value on your data table to two decimal places.

4. Carefully add NaOH from the buret to the Erlenmeyer flask with swirling.

5. Add NaOH drop-by-drop near the end point, using a white piece of paper under the flask to help observe a sharp color change.

6. Record the final buret reading.

7. Repeat as necessary until three consistent volumes have been recorded.

PART C: Cleaning the buret.

1. Is is imperative that you thoroughly clean your buret after you have finished titrating.  

2. Empty out the leftover NaOH solution.

3. Rinse thoroughly with tap water first.  Be sure to run the water through the stopcock.

4. Then, rinse the buret with distilled water.  Again, be sure to run distilled water through the stopcock.

Data Table

Directions: Prepare a word-processed, printed data table (copy/paste) as you've done before.  Include the Part A data table, the Part B data table.  Then, at the bottom, copy/paste the three Analysis questions with space enough to answer them.

PART A - Sodium hydroxide

PART B

Analysis

Turn in your completed data table and also answer these three questions.

1. Write the balanced equation for the reaction of NaOH with HCl.

2. Use your data to calculate an accurate concentration for the hydrochloric acid solution.  Calculate the molarity for EACH titration trial.  Show all of your work!  After you have shown all your work, record the value in the data table above.

3. Calculate the STANDARD DEVIATION for the molarity results obtained in this experiment.  See Thinkwell website titration simulation for a review on how to calculate this!  Show your work! After you have shown all your work, record the average molarity + standard deviation in the data table above.