Course Content
Matter
OBJECTIVES By the end of this topic, the trainee should be able to 1.Define matter 2.Explain state of matter 3.Distinguish between physical and chemical changes 4.Explain the gas laws
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Atoms , Elements and Compounds
OBJECTIVES By the end of this topic , the trainee should be able to; 1.Define Elements, Compounds and Mixtures 2.Describe the structure of an atom 3.Describe how to determine the Atomic number ,Mass number and Isotopes
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The Periodic Table
OBECTIVES By the end of this topic, the trainee should be able to : 1.State the historical contribution on development of the periodic table 2.Explain the periodic trends of elements and their compounds 3.State the diagonal relationships of the periodic table
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The S-Block Element
OBJECTIVES By the end of this topic, the trainee should be able to: 1.Explain the chemistry of group I and II elements 2.State the application of group I and two elements and their compounds
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Chemical Bonds
OBJECTIVES By the end of these topic, the trainee should be able to 1.Identify different types of bonds 2.Describe their properties
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Chemical Equilibrium
OBJECTIVES By the end of this topic , the trainee should be able to : 1.Define chemical equilibria 2.Explain types of equilibria 3.Determine equilibrium constant 4.Describe factors affecting chemical equilibrium
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Introduction To Organic Chemistry
By the end of this topic , the trainee should be able to : 1.Explain the aspects of organic chemistry 2.Describe hydrocarbons 3.Classify organic molecules explain chemical reactions of simple organic molecules 4.Explain the properties , synthesis and uses of simple organic molecules
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Acids, Bases and Salts
OBJECTIVES By the end of this session , the trainee should be able to : 1.State properties of acids and bases 2.Differentiate between strong and weak acids 3.Explain types and properties of salts
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PH Analysis
OBJECTIVES By the end of this topic, the trainee should be able to: 1.Define the term PH 2.Explain the basic theory of PH 3.State the relationship between PH and color change in indicators 4.Explain the term buffer solution 5.Describe the preparation of buffer solutions 6.State the application of buffer solutions
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Sampling and Sample Preparation
OBJECTIVE By the end of this topic, the trainee should be able to : 1.Define the terms used in sample preparation 2.State the importance of sampling 3.Describe the techniques of sampling 4.Describe the procedure for sample pre-treatment 5.State sample storage methods
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Separation Techniques
OBJECTIVES By the end of this topic , the trainee should be able to : 1.Define separation, extraction and purification 2.Describe the separation , extraction and purification techniques 3.Explain the methods of determining purity of substances
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Heating and Cooling Techniques
OBJECTIVES To identify various techniques used for heating and cooling substances in the laboratory
Heating and Cooling Techniques
OBJECTIVES To identify various techniques used for heating and cooling substances in the laboratory
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Distillation Techniques
By end of this topic, Trainee should be able to : 1. Define distilation 2. State and explain various distillation techniques 3. Outline Various distillation techniques 4. Outline the applications of Distillation techniques
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Crystallization Techniques
OBJECTIVES By the end of the topic, the learner should be able to: 1.To define crystallization 2.To describe crystallization process 3.To carry out crystallization procedure
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Solvent Extraction Techniques
OBJECTIVES By the end of the topic, the learner should be able to 1.Define solvent extraction 2.Explain terms used in solvent extraction 3.Describe methods of solvent extraction 4.Describe selection of appropriate solvents for solvent extraction 5.Determine distribution ration 6.Outline factors actors influencing the extraction efficiency 7.Describe Soxhlet extraction
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Chromatography Techniques
OBJECTIVES By the end of this topic, the learner should be able to: 1.Define chromatography techniques 2.Explain terms used in chromatography techniques 3.Describe principles of chromatography techniques 4.Explain types of chromatography techniques 5.Carry out chromatography experiments 6.Determine RF factor 7.Outline electrophoresis
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Titrimetric Analysis
OBJECTIVES By the end of this topic, the trainee should be able to: 1.Define terms used in titrimetric analysis 2.Describe types of titrimetric analysis 3.Balance chemical reactions 4.Work out calculations involved in titrimetric analysis
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Redox Titration
Redox Titration is a laboratory method of determining the concentration of a given analyte by causing a redox reaction between the titrant and the analyte. Redox titration is based on an oxidation-reduction reaction between the titrant and the analyte. It is one of the most common laboratory methods used to identify the concentration of unknown analytes. Redox reactions involve both oxidation and reduction. The key features of reduction and oxidation are discussed below.
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Complexiometric Titration
omplexometric Titration or chelatometry is a type of volumetric analysis wherein the colored complex is used to determine the endpoint of the titration. The method is particularly useful for determination of the exact number of a mixture of different metal ions, especially calcium and magnesium ions present in water in solution .
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Gravimetric Analysis
OBJECTIVES By the end of this topic, the trainee should be able to: 1.Define gravimetric analysis 2.Describe the principles of gravimetric analysis 3.Describe the steps involved in gravimetric analysis 4.Explain factors affecting gravimetric analysis 5.Describe the equipments and apparatus used in gravimetric analysis 6.Carry out gravimetric analysis
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Calorimetric Analysis
OBJECTIVES By the end of this topic, the trainee should be able to: 1.Define terms and units used in thermochemistry 2.Determine enthalpy changes in chemical reactions 3.Determine heat capacity and specific heat capacity 4.Compare calorific values of different materials 5.Determine different heat reactions 6.Apply law of conservation of energy and Hess law in thermochemical calculations
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Chemistry Techniques for Science Laboratory Technicians
About Lesson

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INTRODUCTION

In the previous sections, we have learnt that a substance is an acid if it furnishes H+ ions in its aqueous solution and a base if it furnishes OH ions. Water plays very important role in these processes, we shall learnt about it in this section.

Dissociation Of Acids And Bases

If a dry strip of blue litmus paper is brought near the mouth of the test tube containing dry HCl gas , its colour does not changes. When it is moistened with a drop of water and again brought near the mouth of the test tube , its colour turns red. It shows that there are no H+ ion in dry HCl gas. Only when it dissolves in water, H+ ions are formed and it shows its acidic nature by turning the colour of the blue litmus paper to red.

A similar behavior is exhibited by bases. If we take a pallet of dry NaOH in dry atmosphere and quickly bring a dry strip of red litmus paper in its contact, no colour change is observed. NaOH is a hygroscopic compound and soon absorbs moisture from air and becomes wet. When this happens, the colour of the red litmus paper immediately changes to blue. Thus in dry solid NaOH although OH ions are present but they are not free and do not show basic nature on coming in contact with water, OH  ions becomes free and show the basic nature by changing red litmus blue. From the above discussion, it is clear that acidic and basic characters of different substances can be observed only when they are dissolved in water.

  • When an acid like sulphuric acid or a base like sodium hydroxide is dissolved in water, the solution that is formed is hotter. It shows that the dissolution process is exothermic. A part of the thermal energy which is released during the dissolution process is used up in overcoming the forces holding the hydrogen atom or hydroxyl group in the molecule of the acid or the base in breaking the chemical bond holding them and results in the formation of free H+(aq) and OH(aq) ions.
  • Many bases are ionic compounds and consist of ions even in the solid state. For example sodium hydroxide consists of Na+and OH These ions are held very tightly due to the strong electrostatic forces between the oppositely charged ions. Presence of water as a medium (solvent) weakens these forces greatly and the ions become free to dissolve in water.

Self dissociation of water

Water plays an important role in acid base chemistry, it helps in the dissociation of acids and bases resulting in the formation of H+(aq) and OH (aq) ions respectively. Water itself undergoes dissociation process which is called ‘self-dissociation of water’.

Water dissociates into H+(aq) and OH(aq) ions as:

                           H2O(l)  H+ (aq) + OH (aq)

The dissociation of water is extremely small and only about two out of every billion (109) water molecules are dissociated at 25°C. As a result, the concentrations of H+(aq) and OH(aq) ions formed is also extremely low. At 25°C (298K),

[H+] = [OH] = 1.0 × 10–7 mol L–1

Here, square brackets denote the molar concentration of the species enclosed within. Thus, [H+] denotes the concentration of H+(aq) ions in moles per litre and [OH] the concentration of OH(aq) ions in moles per litre.

It must be noted here that in pure water and in all aqueous neutral solutions,

[H+] = [OH]

Also, in pure water as well as in all aqueous solutions at a given temperature, product of concentrations of H+(aq) and OH(aq) always remains constant. This product is called ‘ionic product of water’ and is given the symbol Kw. It is also called ionic product constant of water. Thus,

Kw = [H+] [OH]

At 25°C (298 K), in pure water, Kw can be calculated as:

Kw = (1.0 × 10–7) × (1.0 × 10–7) = 1.0 × 10–14

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