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Chapter

Cover Core Maths for the Biosciences

Molarity and dilutions  

This chapter sets out the calculations required to work effectively with materials in solutions. It explains that a solution consists of a certain amount of solid or liquid chemical, called solutes, dissolved in a volume of liquid, called the solvent, which for biological purposes is usually water. It also defines the molar mass of a substance as the mass (in grams) of one mole of the substance, noting that the mass of a substance can help determine the number of moles and molecules present. The chapter points out that, as each molecule is made up of atoms, the mass required for one mole can easily be determined by addition of the masses of the individual atoms that make up the molecule. It discusses the concept of moles, which determines the concentration of solutions in terms of how many moles of a substance are contained in a solution; this is called molarity of the solution.

Chapter

Cover Making the Transition to University Chemistry

Moles  

This chapter explores different types of formulae in chemistry: empirical formula and molecular formula. It defines empirical formula as the simplest whole-number ratio of atoms of each element in a compound. Molecular formula can be defined as the whole-number multiple of the empirical formula. The chapter also explains the value of the Avogadro constant, which is the number of atoms per mole. It notes the strategies for solving mass-to-mass calculations, ideal gas models, molar concentration, and molar volume. Molar mass is defined as the mass per mole of a substance. A solution is mostly expressed through mass concentration. This specifies the mass of the solute dissolved per cubic decimetre of the solution.

Chapter

Cover Polymers

Polymer properties and characterization  

This chapter discusses the properties and characterization of polymers. The techniques most commonly used to determine polymer molar mass include end-group analysis, osmometry, light scattering, ultracentrifugation, sedimentation, viscometry, and chromatography. However, most of these involve rather lengthy procedures and in practice molar masses are obtained from high performance gel permeation chromatography (HPGPC) or viscosity measurements. It is important to recognize that the fundamental measurements of molar mass must be performed on dilute solutions so that intermolecular interactions can be ignored. The chapter then looks at polymer stereochemistry; structure-property relationships; and polymer processing. It also considers the thermal methods of polymer analysis, in which some physical property of a substance is measured as a function of temperature or time while the substance is subject to a controlled temperature programme. The most common techniques are differential scanning calorimetry, thermal gravimetry, dynamic mechanical analysis, dilatometry, heat-deflection temperature, and melt index.

Chapter

Cover Chemistry for the Biosciences

Moles, concentrations, and dilutions: making sense of chemical numbers  

This chapter details the language of measuring chemical quantities, focusing on one quantity in particular: the mole. The mole is a convenient way of scaling down large numbers: one mole of atoms represents 6 × 1023 atoms. The molar mass is the mass of one mole of a substance. The concentration of a solution tells us how much of a substance is present in a particular volume of that solution. When preparing solutions according to percentage by weight, one uses a mass of substance that equates to a certain percentage of the volume of the final solution. The chapter then looks at dilutions, explaining how the number of moles of the solute remain the same after dilution, but the total volume increases, so the concentration decreases. The chapter also highlights some of the tools for measuring concentrations, including titrations, UV-visible spectroscopy, atomic emission spectroscopy, and fluorescence spectroscopy.