Protocol for Practical Classes

Subject: pH e tampões

Experiment 2 - Titulation

Materials:

pH meter;

30 mL of NaOH 0,1mol/L solution;

30 mL acetic acid 0,1mol/L solution;

A bequer;

A pippete .

Metods:

Put 30ml of the acetic acid 0,1mol/L solution on a bequer

Measure its pH using the pH meter:

Check if the pH meter is already calibrated

Raise the handspike with the electrode– CARE– FRAGILE >

Put a bequer with distilled water under the electrode

Wash the electrode in the distilled water (the electrode can not hit the bequer)

Put the bequer containning the solution to be measured under the electrode

Doen the handspike until dive the handspike of the electrode in the solution. Make sure the electrode doesn't hit the bequer.

Activate the lectute botton to start the measure. Wirtie down the value.

Add 3,0 ml of the NaOH solution some times and measure the pH of the soultion again after each adding.

Remeber that youmust wash the electrode after each measure (change the distilled water after some measures).

Buid a grephic (a curve) with the data collectes (H+ equivalents x pH).

Objectives

To understand and get used to the pH meter

To characterize buffering and its formation on weak acids solutions

To practice titulation.

Report suggestions:

Analyse the pH variation on a buffer solution when a strong base is added.

Build a titulation curve, showing the pH variation and the buffer band. Why does it occur and how important it is on biological systems.

Build a theorethical titulation curve and compare it to the obtained.

For more references:

http://yip5.chem.wfu.edu/yip/java/titrate.html

http://yip5.chem.wfu.edu/yip/java/j01/titrate3.html

http://yip5.chem.wfu.edu/yip/java/titrate5.html