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Chapter

Cover Elements of Physical Chemistry

Solubility equilibria  

This chapter highlights solubility equilibria. A solid dissolves in a solvent until the solution and the solid solute are in equilibrium. At this stage, the solution is said to be saturated, and its molar concentration is the molar solubility of the solid. That the two phases—the solid solute and the solution—are in dynamic equilibrium implies that equilibrium concepts can be used to discuss the composition of the saturated solution. A solubility equilibrium is an example of a heterogeneous equilibrium in which the species are in different phases (the solid solute and the solution). The chapter then looks at the solubility constant before considering the common-ion effect. The common-ion effect is the reduction in solubility of a sparingly soluble salt by the presence of a common ion. The chapter also examines the effect of added salts on solubility.

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 Biomedical Science Practice

Preparing and measuring reagents  

Ian Graham

This chapter details the process of preparing and measuring reagents, which are essential and fundamental skills for all biomedical scientists. The use of balances for weighing and pipettors and other volume measurement methods for volume delivery are key techniques in the production of solutions and their dilution. For correct operation, balances must be appropriately sited and calibrated. Burettes, pipettes, and volumetric flasks provide high levels of accuracy if used correctly. However, pipettors are the volume measurement tool of choice for highly accurate and precise work. They use disposable tips for convenience, require calibration, and, being precision instruments, must be used with care. The chapter then looks at molar concentrations and alternative ways of expressing concentration.

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.