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
Molarity and dilutions
Chapter
Polyprotic acids
This chapter explores polyprotic acids. A polyprotic acid is a molecular compound that can
donate more than one proton. It is best considered to be a molecular species that can give
rise to a series of Brønsted acids as it donates a succession of protons. The chapter begins
by looking at the process of successive deprotonation. Enzymes are polyprotic acids, for
they possess many protons that can be donated to a substrate molecule or to the surrounding
aqueous medium of the cell. For them, successive acidity constants vary much less because
the molecules are so large that the loss of a proton from one part of the molecule has
little effect on the ease with which another some distance away may be lost. The chapter
then considers speciation, which is the specification of the fractional composition of ions
in a solution.
Chapter
Reactions in solution
This chapter explains that most chemical reactions take place in solution, and so it is
important to understand what controls their rates. The concept of the rate-determining step
plays an important role for reactions in solution where it leads to the distinction between
‘diffusion control’ and ‘activation control’. In the diffusion-controlled limit, the
condition for the encounter rate to be rate-determining is not that it is the slowest step,
but that the reaction rate of the encounter pair is much greater than the rate at which the
pair breaks up without reacting. In the activation-controlled limit, the condition for the
rate of energy accumulation to be rate-determining is a competition between the rate of
reaction of the pair and the rate at which the pair breaks up, and all three rate constants
control the overall rate. The chapter then looks at Fick's first law of diffusion and Fick's
second law of diffusion.
Book
Modern Liquid Phase Kinetics aims to show that the world is not at equilibrium, and the events that give vitality and movement are transitions towards equilibrium from the present state of imbalance. Chemical transformations often contribute fundamentally to this process and their study is challenging and important. The early chapters of this text provide a basic introduction to the kinetics of simple and complex reaction systems in solution. The remaining chapters present a treatment of the more advanced topics, comprising solvent effects, fast reaction techniques, and heterogeneous liquid—liquid two-phase systems. The last introduces currently active and important research areas in solution kinetics, including phase-transfer catalysis, and diffusion and transport in chemical and biological membranes.
Chapter
Colligative properties
This chapter evaluates colligative properties. A colligative property is a property that
depends on the number of solute particles, not their chemical identity; they arise from the
effect of a solute on the entropy of the solution. Colligative properties include lowering
of vapour pressure, depression of freezing point, elevation of boiling point, and osmosis.
The phenomenon of osmosis is the passage of a pure solvent into a solution separated from it
by a ‘semipermeable’ membrane, a membrane that is permeable to the solvent but not to the
solute. The osmotic pressure is the pressure that must be applied to the solution to stop
the inward flow of solvent. The chapter then considers how the van 't Hoff equation
expresses the osmotic pressure in terms of the concentration of solute in the solution.
Chapter
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
Acid–base Equilibrium
This chapter explains the acid-base equilibrium. This involves the transfer of protons in line with the Brønsted–Lowry theory. A strong acid or strong base is fully ionized in an aqueous solution, while weak acids or bases are only partially ionized in an aqueous solution. Acid-base titrations measure the unknown concentration of one solution by reaction with another standard solution with a familiar concentration. The chapter also notes how indicators are typically water-soluble weak organic acids with varying colours at different pH values. It explores the alternative theory of acid-base reactions proposed by Gilbert Lewis: a Lewis acid is an electron-pair acceptor, while a Lewis base is an electron-pair donor.
