Calculations Using Normality and Equivalent Weight

Volumetric Calculations Using Normality and Equivalent Weight... 

Appendix 4 Formation Constants at 25°C A-10 Appendix 5 Standard and Formal Electrode Potentials A-12 Appendix 6 Use of Exponential Numbers and Logarithms A-15 Appendix 7 Volumetric Calculations Using Normality and Equivalent Weight A-19... 

Throughout this text, we base volumetric calculations exclusively on molarity and molar masses. We have also included in Appendix 6 a discussion of how volumetric calculations are performed ba.sed on normality and equivalent weights because you may encounter these terms and their uses in the industrial and health science literature. 

To learn about normality and equivalent weight. To learn to use these concepts in stoichiometric calculations. 

We shall use molarity throughout the majority of the text for volumetric calculations. However, another useful concentration unit for volumetric calculations is normality, which uses the concepts of equivalents and equivalent weights in place of moles and formula weights. Normal concentration depends on the particular reaction, and the reaction should be specified. Some instructors prefer to introduce the concept of normality, and students are likely to encounter it in reference bop. Therefore, a review of equivalents and normality is given following the discussion of calculations using molarity. 

The problem can, of course, also be worked using equivalents and normal- equivalents and milliequivalent ity. To illustrate this approach, the calculation is given. The equivalent weight of weights. 

Many of the commercial reactants used in urethane synthesis are impure materials, for example MDI may be used as pure MDI, a low melting-point (38°C) solid polymeric or crude MDI, which is a dark-coloured low viscosity liquid. Alternatively, MDI and TDI prepolymers may be blended and perhaps have various additives incorporated, all of which may affect the final quantity of free NCO available for reaction. Also, active isocyanate content of a prepolymer decreases with storage, a decrease of about 0-05% per month being normal. For these reasons it is necessary to measure and specify the amount of isocyanate available for reaction at any specific time, and this is done by calculation of the isocyanate equivalent weight of the mixture using the following procedure ... 

Any calculation that can be carried out with equivalent weights and normality can also be done by the mole method using molarity. The methods of this section are widely used, however, in health-related fields and in many industrial laboratories. 

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