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Soaps and Emulsions - Education Scotland

By Mildred Barnes,2014-01-29 04:57
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Soaps and Emulsions - Education Scotlandand,soaps,SOAPS,AND,Soaps

NATIONAL QUALIFICATIONS CURRICULUM SUPPORT

    Chemistry

    Soaps and Emulsions

    [HIGHER]

    The Scottish Qualifications Authority regularly reviews

    the arrangements for National Qualifications. Users of

    all NQ support materials, whether published by

    Learning and Teaching Scotland or others, are

    reminded that it is their responsibility to check that the

    support materials correspond to the requirements of the

    current arrangements.

Acknowledgement

    Learning and Teaching Scotland gratefully acknowledges this contribution to the National

    Qualifications support programme for Chemistry.

? Learning and Teaching Scotland 2011

This resource may be reproduced in whole or in part for educational purposes by educational

    establishments in Scotland provided that no profit accrues at any stage.

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     ? Learning and Teaching Scotland 2011

Contents

    Introduction 4

    Section 1: Making soap 5 Making soap 5

    The structure of soap 7

    How soaps work 7

    Section 2: The cleansing action of soaps 9 Definition: the engine of the detergent system 9 Structure and composition 10

    How surfactants work 10 What is surface tension and how does a surfactant lower it? 10

    How does a surfactant reduce the interfacial tension between oil and water?

     11

    Mechanism of stain/dirt removal 12 Roll-up mechanism 12

    The structure of a micelle 12

    Solubilisation 13

    Electrostatic interactions 13

    Types of surfactant 14 Structural examples of the head groups (hydrophil) 14

    Section 3: Emulsions 15 What is an emulsion? 15

    How do emulsifiers work? 17

    Making an emulsifier 19

    How an emulsion is made 20

    SOAPS AND EMULSIONS (H, CHEMISTRY) 3

     ? Learning and Teaching Scotland 2011

INTRODUCTION

Introduction

    The following document has been designed as a guide for practitioners teaching section 7 of the Consumer Chemistry component of Higher Chemistry. This document can be used to explain specific examples to a more in-depth level or to explain general concepts.

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    SECTION 1: MAKING SOAP

Section 1: Making soap

Making soap

    Soaps are formed by the alkaline hydrolysis of fats and oils by sodium or potassium hydroxide by boiling under reflux conditions:

    The glycerol released is separated and used as a raw material for other processes:

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     ? Learning and Teaching Scotland 2011

SECTION 1: MAKING SOAP

    The fatty acids are produced in the form of their sodium or potassium salts. These salts are called soap.

    Soap

    The long covalent hydrocarbon chain that makes up the tail section of a soap structure can be represented in a number of ways, either in the shorthand notation shown below or as a bond-stick representation, shown at the bottom of the page. The charged carboxylate group represents the head section of the soap structure.

    Soap

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    SECTION 1: MAKING SOAP

    The structure of soap

    The long covalent hydrocarbon chain gives rise to the hydrophobic (water hating) and oil-soluble (non-polar) properties of the soap molecule (represented in yellow). The charged carboxylate group (represented in blue) is attracted to water molecules (hydrophilic). In this way, soaps are composed of a hydrophilic head and a hydrophobic tail:

How soaps work

    The following ball (blue for hydrophilic head group) and stick (yellow for hydrophobic tail group) diagram represents the initial interaction of soap on addition to water and material with a grease stain:

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     ? Learning and Teaching Scotland 2011

SECTION 1: MAKING SOAP

    When the solution containing soap and water is agitated (stirred vigorously) the interactions of hydrophobicity and hydrophilicity become apparent. The hydrophobic, non-polar, tails burrow into the greasy, non-polar molecule

    like attracting like. In the same way the polar hydrophilic head groups are attracted to polar water molecules. The head groups all point up into the water at the top of the grease stain.

    The attraction of the head group to the surrounding water, via polar-to-polar interactions, is so strong that it causes mechanical lift of the grease molecule away from the material on which it was deposited. The hydrophobic tails are anchored into the grease due to non-polar to non-polar attraction. In combination, these effects allow for the removal of the grease stain.

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    SECTION 2: CLEANSING ACTION OF SOAPS

    Section 2: The cleansing action of soaps

Definition: the engine of the detergent system

    When used for cleaning in combination with water, soap serves as a surfactant. Surfactants are the main contributors to detergents cleaning

    performance.

    The bulk components of detergents are surfactants; other key ingredients include:

    ; bleach, to enhance the appearance and effect of whiteness ; polymers, for binding to and removing certain types of dirt ; builders: to provide the formulations (liquids, gels, capsules and tablets) with consistency

    ; enzymes, to remove biological stains, including, blood, wine, chocolate and coffee.

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     ? Learning and Teaching Scotland 2011

SECTION 2: CLEANSING ACTION OF SOAPS

    Structure and composition

    A broad definition of a surfactant is: a substance, such as soap, that possesses a hydrophobic tail and a hydrophilic head and which, on being made into a solution with water, reduces the surface tension of water and also reduces the

    interfacial tension between oil and water.

How surfactants work

What is surface tension and how does a surfactant lower it?

    The surface tension of water can be seen in the picture below. The cohesion between the water molecules is strong enough to allow relatively dense objects to be suspended above the water line.

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