What is oxidation?

\(\require{mhchem}\) Oxidation for the chemist can be defined in lots of ways. The most obvious is: addition of oxygen. If we burn magnesium in oxygen... $$\ce{magnesium + oxygen -> magnesium~oxide}$$ $$\begin{equation} \ce{2Mg(s) + O2(g) -> MgO(s)} \end{equation}$$ The magnesium gains oxygen and is oxidised. Students are often taught the mnemonic OILRIG, which tells us Oxidation Is Loss. This refers to electrons. So our second definition is oxidation is loss of electrons. If we look at what happens to magnesium atoms in that same reaction, we can see that they are oxidised by losing electrons to form positive ions. $$\begin{equation} \ce{Mg -> Mg^2+ + 2e-} \end{equation}$$ Another definition of oxidation is removal of hydrogen. In organic chemistry an alcohol can be oxidised to an aldehyde, and in this reaction hydrogens atoms are removed. $$\begin{equation} \ce{CH3CH2OH +[O] -> CH3CHO + H2O } \end{equation}$$ where [O] represents an oxidising agent. Finally we can use oxidation states to see when oxidation happens. If the oxidation state increases, oxidation has occurred. $$\begin{equation} \ce{Mg -> Mg^2+ + 2e-} \end{equation}$$ In this equation magnesium has gone from an oxidation sate of 0 to +2, so has again been oxidised. Our fourth definition is oxidation is an increase in oxidation state.

Comments

Post a Comment

Popular posts from this blog

How to do calculations in science

\(\require{mhchem}\) Example 1. Speed, distance, and time Problem How long does it take a bee flying at 20 m/s to cover a distance of 100 m? List what you know $$s = 20~\ce{m/s}, d = 100~\ce{m}, t = ?$$ Write out the equation speed = distance / time, $$s=\frac{d}{t}$$ Substitute in your values $$20=\frac{100}{t}$$ Rearrange if necessary Multiply both sides by t. $$20t = 100$$ Divide both sides by 20. $$t = \frac{100}{20}$$ Calculate your answer $$t = 5$$ Check and format the answer, showing units. Is your answer sensible? $$t = 5~\ce{s}$$ (no requirements in the question for decimal places or significant figures). Sensible = yes. Check by backwards calculation. $$s=\frac{100}{5}=20~\ce{m/s}$$ Correct. Example 2. Concentration, volume, and number of moles Problem ...
Read more

Reduction and oxidation (redox)

\(\require{mhchem}\) Reduction can be: removal of oxygen; addition of hydrogen; gain of electrons. We often want to reduce metal ores to get the useful metals from them. Oxidation can be: addition of oxygen; removal of hydrogen; loss of electrons. A substance that reduces another substance is a reducing agent . And guess what? A substance that oxidises another substance is an oxidising agent . Reduction and oxidation always go hand in hand. If a reducing agent like \(\ce{H2}\) acts on a substance (let's say oxygen \(\ce{O2}\)), oxygen is reduced, but in doing so hydrogen is oxidised. $$\ce{hydrogen + oxygen -> water}$$ $$\begin{equation} \ce{2H2(g) + O2(g) -> 2H2O(g)} \end{equation}\label{water}$$ (I've made the water a gas here because when you burn hydrogen in oxygen, things get hot, and the water is produced as vapour.) If we look at equation \(\eqref{water}\) from the point of view of oxygen, we can think of oxygen as the oxidising agent which oxidises hydrogen,...
Read more

Balancing chemical equations

We must have the same number of atoms on both sides of a chemical equation's arrow. Why? If we didn't we would be creating or destroying atoms, and that's not possible. The Law Of Conservation Of Mass tells us that matter (in this case atoms) cannot be created nor destroyed. So when we count up the number of atoms on each side of the arrow, they must be the same . Also, the number of atoms of each element must be the same. In a chemical reaction, the atoms are rearranged, but they can't change from one element to another. A carbon atom in a reactant on the left side of the arrow remains a carbon when it changes to a product on the right side of the arrow. It doesn't suddenly become a different element. Sidenote: when we have radioactive elements, changes happen in the nucleus of the atom that mean that an atom of a radioactive element can decay to form a different element. And in stars, at immense temperatures, the nuclei of two atoms may fuse together to make a he...
Read more