Dr Hall's Chemistry Blog (copy)

\(\require{mhchem}\) 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 ...

\(\require{mhchem}\) 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 ...