 HCl is a strong acid. We should be very careful with this. Whereas vinegar is a weak acid. We even eat this. But what is the difference? What makes an acid strong or weak? That's exactly what we are going to talk about in this particular video. See, we have already studied that acids are compounds which when mixed in aqua solution, they increase the concentration of H plus ions. And that's why when I mix HCl in water, this dissociates into H plus and chlorine minus. And it increases the H plus ion concentration. That's why this is an acid. But HCl is a strong acid. Meaning it goes through complete dissociation. This means that if I take 10 molecules of HCl, all of the HCl molecules will break down or dissociate into its ions. I will have no HCl molecule being left behind. In fact, I will get 10 H plus and 10 chlorine minus. That means a strong acid. It completely dissociates in an aqua solution into its ions. And we no longer have any molecules of the acid present in the solution. We will only get its ions in the solution. Whereas if you take a weak acid like vinegar, see its chemical formula is CH3COOH called acetic acid. See, this is also an acid. So when mixed in an aqua solution, this will also dissociate to give us H plus ion. We will get H plus and CH3COO minus ion, acetate ion. But see, there is a problem. This acetate ion is not very stable in its ionic form. It doesn't want to stay as an ion. It will combine with H plus. And it will want to exist as the acid. This means even if you take 10 molecules of acetic acid, not all of them are going to dissociate to give us H plus ion. Even after a long time, you can find a lot of acid still existing. Acid molecules still in the solution. Let's say maybe 8 molecules are still in the solution. And only 2 molecules have dissociated to give us H plus and acetate ion. The rest of the molecules would have dissociated, but their ions would have combined back to give us the acid molecule. Okay? So this is the difference between strong acid and weak acid. See, strong acids, they undergo complete dissociation. Meaning all the molecules of the acid will dissociate to give us H plus ion. And no molecules of the acid will remain back in the solution. Whereas weak acids, they only undergo partial dissociation. Meaning not all molecules. In fact, only few molecules of the acid will dissociate to give us H plus ion. And that is happening because the negative ion that gets formed is very unstable. It combines back with the H plus to give back the acid. Okay? Now this means that if I take equal amount of strong acid, this will give me a lot more H plus ions than the equal amount of weak acid. In fact weak acids, they give us very little amount of H plus ions. And that's why they are less harmful or less dangerous to human body. And strong acids, since they give a lot of H plus ion, they could be very dangerous to human body. Because see, human body, it tries to maintain the acidity of the body. Or the concentration of H plus ions in the body. And whenever it comes in contact with even small amount of strong acid, it could increase the concentration of H plus ions in the body. And therefore, it can harm the human body. That's why we suggest you know, be very careful around strong acids. Later on we will study how to dilute the strong acids and use them safely. But for now, let's look at some examples of strong acid and weak acids. So strong acid apart from HCl is H2SO4, HNO3 and other acids. See all of these acids, they completely dissociate. Meaning you would not find their molecules present in the solution. You will only find their ions being present in the solution. Whereas examples of weak acid, apart from acetic acid, are H2CO3 and HF. And there are some other acids too. See, these acids will only go through partial dissociation. Meaning even if they dissociate most of their ions will combine back to form the acid molecule. And that's why we get very little amount of H plus ions. Now this is something similar that also happens with bases. We have strong bases like NaOH. Now they undergo complete dissociation. Meaning all molecules of the base will dissociate into its ions. Whereas we also have some weak bases like NH4OH ammonium hydroxide. They undergo partial dissociation. Meaning only a few molecules of the base will dissociate into its ions and give us some OH-ion. Now let's summarize the video. In this video we saw that strong acids and bases, they undergo complete dissociation. Meaning all their molecules will dissociate to give us ions. H plus ions and OH-ions. And that's why we will get a lot of them. Whereas weak acids and bases, they will undergo partial dissociation. Meaning only few molecules of theirs will dissociate to give us H plus ions and OH-ions. And that's why we will have very few of them. And we also saw their examples.