Virtual Investigation
Titration of an Acid with a Base

 

Purpose
You will determine the concentration of an acid solution of unknown concentration using a titration.		  
icon Science Skills
checkAnalyzing and Interpreting
icon CAUTION!
Use gloves, safety glasses,
and a lab apron for this activity.

Materials
The following materials are shown in the photographs of this virtual investigation.

  • bromothymol blue (or phenolphthalein)
  • acid solution, containing unknown concentration of HI(aq)
  • 0.100-mol/L NaOH(aq)
  • de-ionized or distilled water in a wash bottle
  • 250-mL beaker
  • 2, 50-mL beakers
  • 125-mL Erlenmeyer flask
  • 10-mL graduated cylinder (or 10-mL pipette and pipette bulb)
  • small liquid funnel
  • 50-mL burette
  • burette clamp
  • ring stand
  • grease pencil (or waterproof marker)

Click on photos to enlarge.

step 1:

Use the grease pencil to label a 50-mL beaker "Acid." Transfer approximately 40 mL of the acid solution (of unknown concentration) to this beaker.

 
step 2:

Use the grease pencil to label another 50-mL beaker "Base Sodium Hydroxide." Transfer approximately 45 mL of the NaOH(aq) to this beaker.

 
step 3:

Attach and secure the burette clamp half-way along the ring stand.

 
step 4:
Remove the burette from the clamp.
Carefully tilt the burette to wash the inside.

Carefully wash the burette. Close the stopcock; then fill the burette one-third full with water from the wash bottle. Tilt the burette sideways to wash the inside walls, then tilt it vertically and hold it over the 250-mL beaker, which will serve as the waste beaker. Open the stopcock and transfer the wash water from the burette into the waste beaker. Repeat this step one more time.

 
step 5:

Place the burette into the burette clamp attached to the ring stand.

 
step 6:
Close the stopcock, place the funnel into the upper end of the burette, and add approximately 15-20 mL of NaOH(aq) to the burette. Remove the funnel from the top of the burette.

 
step 7:

Carefully remove the burette from the clamp; then tilt and wash the inside walls with the sodium hydroxide solution. Return the burette to the clamp, position the waste beaker under the burette, and open the stopcock to drain the burette.

Remove the burette from the clamp.
Carefully tilt the burette to wash the inside.

 
step 8:
Close the stopcock, replace the funnel in the upper end of the burette, and add NaOH(aq) to fill the burette so that the liquid level is within the range of 0 to 5 mL.

 
step 9:

Position the burette so that the level of the NaOH(aq) is at eye level, and measure the position of the lower surface of the meniscus. (You should be able to measure this to at least one decimal place; however, two decimal places is preferred. You might find that using a card with a dark line on it improves the visibility of the bottom of the meniscus.) Record this level in your table.

Results:  

 

 
step 10:

Using either a graduated cylinder or a pipette, transfer 10.0 mL of the acid solution to the 125-mL Erlenmeyer flask.

Measuring the acid solution
Transferring the acid to the flask

 
step 11:

Add 3 to 4 drops of bromothymol blue (or phenolphthalein). Record the colour of the indicator in the acid sample in your table.

 
step 12:

Position the Erlenmeyer flask containing the acid and indicator under the burette; then open the stopcock, and add a small amount of the solution from the burette to the contents of the flask. As you add solution from the burette, swirl the contents of the flask to ensure mixing. Repeat, adding small amounts of solution from the burette to the flask until the indicator changes colour. Record this colour in your table.

Add the first drop of the base.
Swirl the flask while adding the base.
Results: The indicator has changed colour.

 
step 13:

Once a permanent colour change has been reached, position the burette so that the level of the NaOH(aq) is at eye level; then measure the position of the lower surface of the meniscus. Record this level in your table.

Results:  

 
step 14:

Transfer the contents of the Erlenmeyer flask to the waste beaker, rinse the flask with some water from the wash bottle, and repeat steps 8 to 13 to obtain data from three more trials that agree within 0.2 mL.

 
step 15:

Disassemble, wash, and return equipment to its proper location. Repeat step 3 to wash the burette.

 
Note: For students completing the virtual investigation, click here to obtain data.