Category: Big Ideas

Exam questions on chemical analyses (especially titrations) are designed to make you think and test whether you can pull out the key bits of information relevant to a calculation. There will always be lots of detail that you can safely ignore and even very long questions could probably be condensed down to a few bullet…

Many reactions in Chemistry are redox reactions. This means that reduction and oxidation reactions are occuring at the same time, with one substance gaining electrons (reduction) and the other losing electrons (oxidation). You need to be able to work out the balanced symbol equation for a redox reaction, usually starting from with a few bits…

A balanced symbol equation tells us the ratio between the changes in the number of moles of each substance in a reaction. If: 2 C2H6 + 7 O2 –> 4 CO2 + 6 H2O Then: the moles of C2H6, O2, CO2 and H2O change in a 2:7:4:6 ratio. A very common type of question in Chemistry is where we need to calculate the amount of each product formed from…

There are several different ways of calculating moles and you need to be confident with all of them. You’ll usually have to use more than one approach to calculating moles in any given question. I’ve worked through some very straightforward examples to help you practice with each of the equations and ideas. The examples only…

One of the most fundamental skills in Chemistry is being able to look at a chemical formula and understand quickly what it means. e.g., NaCl, K, SiO2, K2O, SiO2, CO2, Cl2, Ar, Xe, Mg(OH)2, Al2(SO4)3.18H2O, I2(s), HCl(aq) Have a little think about the examples above and try to define what we mean by “formula”. It’s…