If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:8:34

Identify salts as neutral, acidic, or basic

Video transcript

- [Instructor] If you believe that salts are always neutral, then you are in for a surprise. See salts, they can be both acidic and basic as well. In this video, we are going to take some salts, and try to identify their nature. So first of all, lets begin with what we already know. So we know that acids and bases, when they react, they neutralize each other's effect. They go under nucleation reaction, and a salt and water is formed, right? We'll also see some examples, like, when HCl reacts with NaOH base, we get the salt NaCl, NaCl salt, and this is a neutral salt, meaning when we put NaCl in water it does not increase the concentration of either H+ or OH- and that's why we call this as a neutral salt. But see, one thing to note over here is that HCl, this is a strong acid, and NaOH, this is a strong base. So what I mean is that when a strong acid and a strong base react, the salt that gets formed is neutral because they both have equally neutralized each other's effect. They both have canceled each other's effect. But you know, if a strong acid is reacting with a weak base, then in that case the salt that gets formed takes the nature of the strong parent. It becomes slightly acidic. And on the other hand, when we have a weak acid reacting with a strong base, it also takes the nature of the strong parent. It becomes basic in nature. And now if you're guessing that a weak acid will react with a weak base to give me a neutral salt, then that's not completely right. See, to understand this we will have to talk about many more concepts so let's not talk about this in this particular video. We'll cover that in a separate video. In this video, let's only cover these three aspects. And if you have a question (mumbles), how are these things happening. Like how is it that a strong acid reacts with a weak base to give me an acidic salt? So we have covered the how part of it in a separate video called the how of this. In this video we will take up some salts and try to identify their nature based on this table. So let's begin. So this is the salt that is given. Sodium acetate, CH₃COONa. And how to find out the nature of this salt, whether this is acidic, basic, or neutral? Well to do that, first of all I'll have to find out what acid and base would have reacted to give me this salt. Then, depending on the nature of the acid and base, I can comment on what will be the nature of this salt, right? So why don't you pause the video and try this by yourself first. Try to figure out what acid and base will react to give me this salt. Now if you have tried it, let's see. So we know that the ions of acid and base, they exchange position and we get salt and water. So to get back the acid and base, we can exchange the ions of salt with water. So let's do that. So water, or H2O, can be written as HOH. Now let's write down the ions of both of these. So the ions of our salt will be CH3COO-, or acetate ion and the sodium plus sign, Na+ and the ions from water, I can write it as H⁺ ion and hydroxide ion, OH⁻ ion. Now let's exchange the ions to get the acid and base. So this time I can combine acetate ion and H⁺ ion, right? I will get CH3COOH, and this is going to be our acid. And now I can combine Na+ and hydroxide ion and I will get my base NaOH, sodium hydroxide. This is our base. So we have found out the parent acid and base for the given salt, sodium acetate, right? So the first step is done. Now the next step is to find out what is the nature of acid and base. Meaning, which of these are strong and weak. So can you pause the video and try to find this out by yourself first? Now if you have tried it, let's see. So you might recall that sodium hydroxide, this is a strong base. Now this means that all the molecules of sodium hydroxide will dissociate, break down and give us ions, sodium ion and hydroxide ion. And if you don't recall the meaning of strong and weak right now, then don't worry. We have talked about this in a great detail in a separate video called Strong and Weak Acid Bases. So I would suggest you to watch that video and then come back here. Okay, if you already are aware of this, let's move ahead. The acid that we have over here, acetic acid, you will recall that this is a weak acid. Now this means that not all the molecules of this acid are going to dissociate. This acid only dissociates partially, okay? Now that we know the nature of parent acid and base, can you guess what is the nature of the salt? Pause the video and think about this. Now if you have thought about this, let's see. So we have seen earlier that the nature of the salt depends on the nature of the strong parent. So over here we have a weak acid but a strong base. That means our salt is also going to be basic in nature. So that's the answer. We have a basic salt, and with this we have solved the problem. So see, the first step was, from the given salt, try to find out the acid and the base that could have reacted upon this. The second step was to find the nature of the given acid and base. And then, the third step was, from this nature, find out the nature of the salt. Now let's try to do one more example. So this time I have the salt NH₄Cl, ammonium chloride, and I have to find out its' nature. So can you pause the video and do all the three steps, and then figure out what is the answer? Pause the video and give it a try. Now if you have tried it, let's see. So the first step was to figure out the parent acid and base that could react to form this salt, right? So we know that ions of acids and bases, they exchange position and then we get salt and water. So one way to find out the acid and base is to exchange the ions between the salt and water. So let's do that. Water I will write it as HOH. Now let's write down the ions of the salt and water. From our salt you will get the ion NH⁺₄ and Cl-, chloride ion. From water I will get H+ and hydroxide, OH-. Now let's exchange the ions. So you have NH⁺₄. This can combine with OH-, this will go with OH-, and I'll get NH4OH and this is going to be a base. This has OH in it, base. And Cl-, chloride ion, will go with H+ and we will get HCl and we know that is an acid. So this is the first step. We have found out the parent base and acid for the given salt. Now the second step was to find out the nature of the base and acid, right? So let's see. We know that HCl, this is a strong acid. HCl is a strong acid. It goes under complete dissociation. And we have also seen that NH4OH, ammonium hydroxide, this is a weak base. This undergoes partial dissociation only. Only a few molecules of this will break into its' ions, okay? So we have a strong acid reacting with a weak base to give us this salt. Now, the third step. Can we figure out what is the nature of the salt? So see, we have seen earlier that the nature of the salt depends on the nature of the strong parent. So here we have a weak base reacting with a strong acid. So the strong parent is the acid. That means our salt is going to be acidic in nature. This is going to be our answer, and we have solved this problem. Now let's summarize the video. In this video we saw that salts could be acidic, basic, or neutral in nature. And the nature depends on the nature of the parent acid and base. We saw that what will be the nature of salt if the acid and base both are strong, and what will be the nature if one of them is strong and the other is weak. I hope you can remember all of these natures, and if you can't, then don't worry. You can go back and watch the video again.