Before you read this, I suggest you read posts 18.1 and 25.6. A buffer keeps the pH of a solution constant. Buffers are used in laboratory experiments and occur naturally in ecosystems and our bodies. A simple laboratory buffer consists of the sodium or potassium salt of a weak acid dissolved in that acid. So… Continue reading 25.7 Buffers
Before you read this, I suggest you read posts 17.49 and 18.3. The extent to which an acid molecule, that I’ll represent as HA, dissociates to give a hydrogen ion (H+) and a cation (A–) depends on its pKa value and the pH of the surrounding solution. We can deduce this statement directly from the… Continue reading 25.6 Henderson-Hasselbach equation
Before you read this, I suggest you read posts 17.49 and 25.4. The purpose of this post is to show how we can use the idea of a resonance hybrid to explain the relative acidity of acetic acid (also called ethanoic acid – the acid that gives vinegar its flavour), ethanol (the alcohol in alcoholic… Continue reading 25.5 Organic acids
Before you read this, I suggest you read post 25.3. I briefly introduced the idea of a resonance hybrid in post 16.31. Since then, I’ve written a lot about resonance, especially in post 18.8. Unfortunately, understanding resonance won’t help you to understand resonance hybrids. Resonance is not involved in the concept of resonance hybrids. I… Continue reading 25.4 Resonance hybrids
Before you read this, I suggest you read post 25.2. The formula of benzene is often written as shown in the picture above. The molecule shown here is a ring of six carbon atoms joined by alternating single and double covalent bonds. There is also a hydrogen atom bonded to each carbon atom. This structure… Continue reading 25.3 Benzene molecule
Before you read this, I suggest you read post 25.1. In post 25.1, I started to describe how the valence bond theory explains how carbon and hydrogen atoms are joined in molecules of ethane, ethene and ethyne (see picture above). My purpose was to introduce the concept of hybrid orbitals. In this post, I am… Continue reading 25.2 Sigma bonds and pi bonds
Before you read this, I suggest you read posts 16.30 and 24.12. I am going to use the bonding in molecules of ethane, ethene and ethyne (see the picture above) to introduce the concept of hybrid orbitals. In post 16.31, we saw that, according to the valence bond theory, a molecule consists of atoms held… Continue reading 25.1 Hybrid orbitals
In post 16.29, we saw that the lowest energy levels in an atom are conventionally labelled, in order of increasing energy, 1s, 2s and 2p. There are three 2p levels that all correspond to the same energy; they are denoted 2px, 2py, and 2pz. Electrons occupy these energy levels according to the principles explained in… Continue reading 24.12 Atomic orbitals
I have written about the first, second and third laws of thermodynamics; these three laws are numbered in chronological order and, I believe, in logical order. But, in 1932, the English physicist Sir Ralph Fowler (1889-1944) proposed that there should be a further law that logically belonged before the other three. So it is called… Continue reading 24.11 Zeroth law of thermodynamics
A more accurate description of this post would be, seeking a single, simple cause for the combined effect of many factors. But this would be a very cumbersome heading. Let’s look at an everyday example: a man is depressed after his wife leaves him. His friends believe he is depressed because his wife left him.… Continue reading 24.10 Multifactorial problems – seeking a cause that doesn’t exist
Thinking about Science with David Hukins 