Estimation of pH - Prelab Questions

Prelab Questions

1. A student performing this experiment added an extra drop of indicator to one of his test tubes. How would this affect his results?

2. Several drops of litmus indicator solution are added to a test tube containing a colorless solution and the solution turned blue. Several drops of thymolphthalein indicator are added and the solution remained colorless. What can be said about the pH of the solution?

3. A student is given two beakers. The first contains a 2 M solution of an acid. The second a 2 M solution of a base.
a. Which has the lowest pH?
b. Which has the highest hydronium ion concentration?
c. In which is the water acting as a base?

4. Solutions of fructose (the sugar found in fruits) and drain cleaner were prepared. The pH's of the solutions were 6.9 and 11.5, respectively. What color should be observed if several drops of the following indicators were added to the solutions? The color change region for each indicator is given in the background.

indicator color in fructose
color in drain
cleaner solution
methyl green _________________ _________________
congo red _________________ _________________
litmus _________________ _________________
phenol red _________________ _________________
thymolphthalien _________________ _________________

5. If you were given the two solutions from question #4 in unlabeled beakers, could you use the information provided by the five indicators to determine which solution was which? Explain.

This completes the prelab. You may begin the experiment.

introduction background prelab experiment postlab