Science Lab Experiment: Acid/Base/Neutral Solutions
Acids and bases
Purpose: To identify substances as acidic, basic or neutral solutions.
hydrochloric acid, HCl phenolphthalein
sodium hydroxide, NaOH red and blue litmus paper
distilled water bromothymol blue
various substances watch glass
glass rod droppers
1. Before doing any tests clean all glassware which you will be using.
2. Place a few drops of solution on a watch glass and test with litmus
paper. Note the results in your data table.
3. Add one drop of phenolphthalein indicator and note the colour in your data table.
Rinse the watch glass, add a few drops of solution a second time and test with one
drop of bromothymol blue. Note results.
4. Rinse watch glass and glass rod and repeat the steps for all other substances.
Litmus paper Red - acidic solution
Blue - basic solution
Phenolphthalein Clear - pH 0 to 8
Pink - pH 8 to 14
Bromothymol blue Yellow - pH 0 to 6
Green - pH 6 to 7.5
Blue - pH 7.5 to 14
Observations: see table.
Blue paper Red paper Phenolphthalein Bromothymol blue Acid, Base or Neutral
pH < > or = 7
Questions: To include in your conclusion
1. What is an indicator ?
2. A few drops of an unknown solution are dropped onto a piece of red litmus
paper and there is no colour change.
a) The student concludes the solution is acidic. Is he correct? Explain.
b) What could he/she do to verify his/her conclusion ?