Protocol for Practical Classes

Subject: pH and buffers

Experiment 1 - pH measures

Materials:

--One assay tube to each student;

--pH indicator strips (to a pH range from 0 to 14);

--Different substances the students must collect around the campus;

--water.

Metods:

Each student collects any material which pH he wants to know, and then dilutes it on water on his assay tube (so, the students must collect substances that are soluble on water or that can be macerated and the mixed into water solutions). Avoid high colors substances, since they can modify the strips colors .

Measure each substance pH.

each grop choose one substance and dilute it more. Then, measure its pH again.

Objectives:

--To classify the substances by pH measures.

--To understand pH as a concentration measure.

--To get used to pH measurements using pH indicator strips.

Report suggestions:

--Group all the substances by pH bands.

--Link types of substances to pH bands.

--Evaluate the pH variation among substances that we use commonly.

--Evaluate the difference between expected and found pH for each substance.

--Try to find how the pH strips work.

--Explain the diluition effect on the pH measure.