Lab 11A: Titration of Hydrochloric Acid SCH 3U

Introduction

Purpose

Apparatus

Materials

Procedure

Observations

Discussion

Conclusion

Links

Procedure:

A. Prepare a data table as shown. Record all your experimental results in the table as soon as you obtain them.

Table Title:
	# 1	# 2	# 3
Concentration of NaOH (mol/L)
Final reading of base buret (mL)
Initial reading of base buret (mL)
Volume of NaOH used (mL)			only if
Final reading of acid buret (mL)			necessary
Initial reading of acid buret (mL)
Volume of HCl used (mL)
Unknown number or letter

B. Obtain about 120 mL of hydrochloric acid solution in a 150 mL beaker. Label the beaker. Rinse one buret with about 5 mL of the solution, and let the liquid drain through the buret tip into an empty 250 mL beaker. Repeat this procedure again, using a new 5 mL sample of the solution. Flush the 10 mls of solution used for washing the buret down the drain with plenty of water.

Fill the buret. Place the buret in a double buret clamp on a retort stand. Let some of the solution run rapidly from the buret to expel all air bubbles from the tip. If this doesn’t get rid of the air bubbles, ask the lab supervisor for help. Do not discard the solution you have just drained – use it to refill the buret. If there is a drop of solution hanging on the buret tip, remove it by touching the drop to the inside wall of the 250 ml beaker. Hold a piece of white paper behind the meniscus, and read the initial volume of the solution at the bottom of the meniscus. Your eye must be at the same level as the meniscus.

C. Obtain about 120 mL of sodium hydroxide solution in a second labelled 150 mL beaker. Obtain a second buret and repeat part B, using the sodium hydroxide solution this time.

D. Accurately measure about 20 mL of hydrochloric acid into a clean 250 mL Erlenmeyer flask. Add two drops of phenolphthalein. Place the Erlenmeyer flask under the tip of the base buret. A piece of white paper placed under the flask will make it easier to see the colour changes. While continuously swirling the flask to ensure thorough mixing (you may use a magnetic stirrer if available), run in the sodium hydroxide solution from the buret. Initially, a pink colour appears at the point where the sodium hydroxide solution comes in contact with the solution in the flask; however, this colour quickly disappears. As the endpoint is approached, the colour disappears more slowly. Eventually, the sodium hydroxide solution should be added drop by drop until one drop turns the entire solution in the flask a light pink. This pink colour should remain at least 15 seconds while the solution is being swirled. If you overshoot the endpoint, add more acid from the acid buret until the solution becomes colourless again. Then add the sodium hydroxide from the base buret until you have the faint pink endpoint. When you have a satisfactory endpoint, read the final volume of each buret.

Refill each buret and repeat part D again, using a clean Erlenmeyer flask.

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