Chemistry – Acids and bases (How to determine strong and weak acids)

There are some common questions on determining weak and strong acids. Yet usually cant find this in textbooks. This is because this type of question spans across a few chapters. 🙂

Most students have no issues understanding that the strength of the acid is indicated by their pH values. But often they miss out that actually the pH values is due to the H+ concentration. 

When the questionn states that universal indicator has ran out and the pH meter has broken down, dont panic. 🙂

We can use the following ways to determine which is a stronger/weaker acid. 

– Enthalpy of neutralisation

Actually, the difference in enthalpy of neutralisation is not large. 
When a weak acid is neutralised, energy is needed to dissociate the molecules, making the hydrogen ions available for neutralisation. This leads to smaller neutralisation enthalpy.
– Conductivity

Acid and base is able to conduct ability to conduct electricity because it contains ions. A strong acid has more ions than a weak one, and so it’s solution will be a better electrical conductor than a weak acid. The same goes for strong/weak bases.

Can use a ammeter to measure the amount of current it conduct. 🙂
– Rate of reaction

In another chapter, we know that the speed of reaction is proportional to the concentration of reactants. In this case, its the concentration of H+ ions if we are comparing strong and weak acids. 

We can use a fixed quantity of metal or metal carbonates to react with the acids and measure the volume of gas evolved. Then plot the volume of gas against time. The gradient of the graph is the speed of reaction. The faster the rate of reaction, the higher the concentration of hydrogen ions and therefore the stronger the acid. 🙂

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