We use the term ‘Dilute acid’. Now, what does it mean?

Dilute acid solution means that acid has been added to water to make an acidic solution. The question is whether acid can maintain its properties when added with water or they undergo changes!

Suppose, you are taken some oxalic acid lattice and put a dry blue litmus paper on them. You will observe no change in the colour of litmus paper. The reason here is that dehydrated oxalic acid lattice does not contain any hydrogen ion.

But, when you dissolve this dehydrated oxalic acid in water, it will decompose and donate H+ ion, which will turn the blue litmus into red colour. That means hydrogen ion present in an aqueous solution shows an acidic property.

Citric acid partially decomposes in aqueous solution and the same thing happens in the case with ethanoic acid and carbonic acid. (Partial decomposition means instead of all molecules added in the solution, some of them decompose and they  remain intact). 

 

Hydrogen chloride (HCl) is completely ionized in aqueous solution and produces hydrogen ion: 

We know, pure sulfuric acid and nitric acid are colourless liquids. Both the compounds remain in their molecular state. Since they are not ionized or hydrogen ion is not present in them, hence, pure sulfuric acid and pure nitric acid neither show acidic properties nor do they conduct electricity. They produce hydrogen ion only when they are dissolved in water, showing acidic property and conducting electricity.

So, we get,

Similarly, we can write, 

The acids that get partially ionized in aqueous solution are weak acids. While Strong acid ionizes completely in aqueous solution.

It shows the weak acids have a lesser amount of hydrogen ion. Strong acids have a comparatively greater number of hydrogen ion.