Chemistry · Ch 1 — Solutions
Introduction
Introduction
Truly pure substances are rare in everyday life. Almost everything around us — the air we breathe, the water we drink, the alloys in our coins and jewellery — is a mixture of two or more pure substances, and how useful or how dangerous that mixture is often depends entirely on the proportion of each ingredient present.
A few real examples make this vivid. Brass (copper + zinc) behaves quite differently from German silver (copper + zinc + nickel) or bronze (copper + tin), even though the metals involved overlap heavily — it is the ratio that changes the material. Fluoride ion concentration in drinking water tells a similar story: about 1 part per million helps protect teeth from decay, but at 1.5 ppm the same ion starts to mottle and stain teeth, and at much higher concentrations fluoride compounds (sodium fluoride, for instance) are outright poisonous — it is even used as a rat poison at high concentration. Medicine depends on this precision too: intravenous fluids are always prepared with salt concentrations carefully matched to blood plasma, because even a modest mismatch can harm the patient.
Almost every process that keeps the human body running happens inside some kind of liquid solution — from blood plasma to the fluid inside every living cell.
What this chapter covers
This chapter focuses mainly on liquid solutions — how they form and how their properties can be measured and predicted. The journey starts with classifying the different types of solutions and learning the various ways chemists express how concentrated a solution is. From there, the chapter builds up to vapour pressure, Raoult's law and Henry's law, the distinction between ideal and non-ideal solutions, and finally the colligative properties — properties that depend only on the number of solute particles present, not on what the solute actually is — which let us work out the molar mass of an unknown solute from simple measurements.
By the end of the chapter you should be able to:
- describe how the different types of solutions (gas-in-gas, solid-in-liquid, and so on) form;
- express the concentration of a solution in several different units and convert between them;
- state and apply Henry's law and Raoult's law;
- tell an ideal solution apart from a non-ideal one, and explain why real solutions deviate from Raoult's law;
- describe the colligative properties of solutions and use them to find the molar mass of a solute;
- explain the abnormal colligative properties shown by solutes that dissociate or associate in solution.