Virtual Investigation
Measuring pH Using Indicators

 

Purpose
You will demonstrate the use of indicators as a means to determine the pH of a solution.
icon Science Skills
checkPerforming and Recording
checkAnalyzing and Interpreting

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

  • 2 copies of the handout "Determining pH Using Indicators"
  • 1 letter-size overhead transparency sheet
  • masking tape
  • dropper bottles (or eyedroppers)
  • solutions with pHs of 1, 3, 5, 7, 9, 11, and 13
  • pH indicators
    – alizarin yellow R
    – thymol blue
    – bromothymol blue
    – bromocresol green
    – methyl orange
  • water containing juice extracted from red cabbage when boiled
  • unknown solutions A, B, and C

Click on photos to enlarge.

icon CAUTION!
Use gloves, safety glasses, and a lab apron for this activity.

Procedure

step 1:

Place one of the handouts on the surface of your work area. Cover the handout with the transparency sheet. Use masking tape to ensure the sheet lays flat and remains attached to the surface of your work area throughout the experiment.

 
step 2:

Place one drop of the solution labelled "pH 1" into each circle in its designated column on the transparency, which is overtop the handout.

 
step 3:

Repeat step 2 with the other pH solutions and the unknown solutions.

 
step 4:

Carefully add a drop of alizarin yellow R indicator to the circles in the first row of the handout. When adding the indicator, ensure that the end of the bottle does not touch the drop of solution already in the circle.

 
step 5:

Repeat step 4 using the other indicators listed in the handout.

 
step 6:

Record the colour of the resulting mixture within each circle in a data table.

Results:

 

 

 
step 7:

Use paper towel to absorb most of the solutions on the transparency; then rinse the transparency in the sink.

 
step 8: Return all apparatus to its proper location in the lab.

Observations

  1. Show your results of this investigation.

Analysis

  1. Use the data to estimate the pH of solutions A, B, and C. Explain how you arrived at your estimation. State a reason why using indicators only results in an estimation of the pH of the three solutions.