Acids, Bases, pH Introduction

1
Acids, Bases, pHIntroduction

• H2O H2O H3O OH -
• by convection we write
• H2O H OH -
• pH 7, neutral
• at equilibrium, H OH -

2
pH

• Scale 0-14
• acid dissociates H , pH below 7
• ex. HCl H Cl -
• base dissociates OH - accepts H ,
• pH above 7
• ex. NaOH Na OH -
• ex. NH3 H NH4

3
Using Indicators to Measure pH

• Anthocyanins plant pigments used as pH
  indicator (cabbage)
• red at low pH
• blue at high pH
• Procedure
• make standards with the following pH buffers and
  record their color
• 2, 4, 6, 7, 8, 10, 12.

4
The pH Meter

• The pH meter is more accurate than indicators.
• Procedure
• determine pH of substances with pH meter and
  litmus paper

5
Buffers

• Buffer prevents sudden pH changes
• Procedure
• determine the buffering capacity of two
  substances (A B)
• Graph your results for AB
• Record which is the better buffer

6
How Effective are Stomach Antacids?

• Antacid used to neutralize excess acid
• Procedure
• compare different antacids
• Rolaids, Tums, Alka-Seltzer
• determine effectiveness of antacids per gram
• (use 0.5 grams of each)
• run a control