Exp' 27 Objectives

1
Exp. 27 Objectives

• To determine the neutralizing effectiveness per
  gram of a commercial antacid.

2
Exp. 27 Introduction

• The purpose of all antacids is to neutralize the
  excess hydrogen ion in the stomach to relieve
  acid indigestion.
• The acidity or basicity of a solution is
  expressed in terms of its pH
• pH lt 7 acidic
• pH gt 7 basic

3
Exp. 27 Introduction

• The pH of stomach acid (HCl) is 1.0-2.0. This
  acid is necessary for digestion and is
  continuously secreted while eating. Therefore,
  overeating can lead to an excess of stomach acid
  and a pH lt1. This, in turn, leads to acid
  indigestion, and possibly irritation of the
  stomach lining, causing heartburn.

4
Exp. 27 Introduction

• An antacid is basic and reacts with the hydronium
  ion, neutralizing the stomach acid and relieving
  symptoms. However, excess use of antacids may
  cause the pH in the stomach to increase to gt2.0,
  causing the stomach to release additional acid.

5
Exp. 27 Introduction

• To decrease the possibility of this happening,
  buffers are often added as part of the
  formulation of the antacid.
• A buffer is a substance that resists large
  changes in pH with the addition of an acid or a
  base.

6
Exp. 27 Introduction

• In this experiment, the neutralizing power of two
  commercial antacids are determined using a strong
  acid-strong base titration. First, the buffer
  action must be destroyed in order to see a
  definite endpoint. This is done with an excess
  of HCl
• HCO3- H3O ? CO2 2H2O
• The solution is heated to drive off the CO2, and
  the remaining HCl is titrated with NaOH.

7
Exp. 27 Introduction

• The number of moles of base in the antacid plus
  the number of moles of base used in the titration
  equals the number of moles of HCl added to the
  original antacid sample, or
• molesantacid molesHCl molesNaOH
• Determining the moles of base in your antacid
  tells you how much acid it can neutralize,
  telling you which antacid is most effective.

8
Exp. 27 Procedural Notes

• Part A the antacid tablets should be colorless
• Part B the 0.1 M NaOH will be prepared for you.
• Two trials each antacid.

9
Exp. 27 Report Sheet

• Questions 1, 3, 4