Properties of acids and bases

0:00- You probably heard of the terms acids and bases, right? But what exactly are they? Well, let's find out. We'll start by thinking of their most primitive definitions, okay? Acids, we thought of them as substances that are sour and sticky. And substances that were bitter and slippery, we call them bases.

0:16So let's take some examples. Sour and sticky. Hmm, the most common ones that come to my mind is lemonade and vinegar. But there could be other, like stomach acid. You also have carbonated drinks. And there could be even more, like vitamin C. You have acids inside the batteries, and even in fertilizers.

0:34They all fall under the category of these acids, okay? What about bases, bitter and slippery? What comes to your mind? Well, soaps and detergents and ammonia, they're all quite slippery, and they're bitter as well. But please don't taste them, okay (laughs)? Baking soda is pretty bitter, but there are other examples like antacids, and there are other kinds of fertilizers that have bases in them.

0:53But now let's go one step further and see if we can be a little bit more rigorous with our definition. So let's go back to our acids. And to do that, let's look at the chemical formulae of all of these and let's see if we can identify something common, okay? Look at all the chemical formula that we have over here.

1:08One thing that you notice is that they all have hydrogen in them. So we could say acids are substances that contain hydrogen. But we could go one step further. If you consider their aqueous solution, for example, aqueous solution of hydrochloric acid, which basically means you dissolve it in water.

1:21When you dissolve something in water, you call it as an aqueous solution, all right? So if you consider the aqueous solution of hydrochloric acid, you know what you'll find inside these solutions? You will find that the H and CI breaks apart, giving you a positively charged hydrogen atom.

1:37We technically call them ions, but don't worry about it. We just call them as positively charged hydrogen atom. And that is what an acid is. Acids are substances that produce positively charged hydrogen atoms in aqueous solution. And remember, this is true for all acids.

1:52Let's take a couple of more examples. Take nitric acid, it's aqueous solution, and you find H+. You take carbonic acid, it's aqueous solution. And again, you find H+, acids produce H+ in aqueous solutions. And in fact, this is the reason why acid stays sour, because it turns out that we have receptors on our tongue that can bind to these positively charged hydrogen atoms when our saliva breaks down certain foods.

2:12And when they do, our brain gives us the sensation of souriness, okay? And so that's what acids are. They produce electrically charged positive hydrogen atoms in aqueous solutions. And similarly, can we now define bases? Well, yeah. Again, look at their chemical formulae.

2:30What do we notice? Well, we notice some bases have OH in their formula. Not all of them. But now what happens when you create their aqueous solution? Well, let's see. If you consider the aqueous solution of sodium hydroxide, meaning you dissolve sodium hydroxide in water, what you find is, again, they break apart, but this time they produce negatively charged molecules.

2:53We call them hydroxide. So we can now say bases are substances that produce hydroxide when dissolved in water or in aqueous solution. By the way, even the bases that do not have OH in their formula actually still produce OH- in an aqueous solution. But in a more indirect way, we'll see in a moment.

3:10So we have our definition. Acids are substances that produce positively charge hydrogen atoms in aqueous solutions, and bases of substances that produce hydroxide, negatively charged OH molecules in aqueous solutions. But remember, these are not complete definitions yet.

3:26For complete definitions, we still have to talk about a property called pH, which we will do in the next video. But for now, this is a good start. Let's talk about some more properties. Since both acids and bases produce electrically charged atoms and molecules, they are electrolytes in aqueous solutions, right?

3:42And therefore they both conduct electricity. Okay, what else? Acids can also corrode stones and metals, and bases can break down oil and grease. That's why they're used in soaps and detergents in the first place. Okay, to understand the last cool property, here's a question.

3:58What do you think will happen if we mix acids and bases together? Well, let's see. Acids produce H+ and bases produce OH-. So what happens when H+ combines with OH-? Well, let's see, you get H, OH, which is, it's H2O. That is water. So acids and bases combine to give us water.

4:20That's incredible, isn't it? So another way to think about bases is that they decrease the amount of H+ in a solution, which is the opposite of what acids do. So remember those bases that didn't have OH in their formula, for example, ammonia? So now look what happens when you put it in water.

4:37It'll remove the H+, giving you NH4+. But what's important is that it'll leave behind OH-. And this is how even the bases that do not have OH in their chemical formula, like ammonia, when you make an echo solution of them, they still produce OH- indirectly. Anyways, because acids and bases work in opposite ways, when we combine them, we say they neutralize each other, and therefore this reaction is called the neutralization reaction.

5:08And when they neutralize each other, we get water. But what else would we get? Well, to answer that question, let's take a concrete example. So let's consider what happens when you combine HCl, which is an acid, with a base like NaOH. Well, we know H and OH combine to give you water.

5:26But what else do we get? Na and Cl will combine to give you an NaCl, which is salt. Which means acid and bases react together to give you salt and water. And this is true for any acid and base. For example, consider an acid, HNO3, which is nitric acid, reacting with KOH, potassium hydroxide, which is a base.

5:47Again, H and OH will combine to give you water, which is H2O. And K and NO3 will combine to give you a salt. So look, you get salt and water. Remember, NaCl is one kind of salt. There are so many other salts. This is also a salt. So putting it all together, acids, we started thinking of them as something that is sour and sticky.

6:08But then we got a little bit more rigorous and realized that they are substances that produce H+, which is electrically charged hydrogen atoms in aqueous solutions. And because they produce electrically charged particles, they're electrolytes, they conduct electricity.

6:21Another cool property is that they can corrode stones and metals. Bases, we started thinking of them as stuff that are bitter and slippery, but then realized, hey, they produce hydroxide, OH-, in aqueous solutions. And again, because they're producing charged particles in solutions, they too conduct electricity.

6:39They too are electrolytes. And their cool property is that they can break down oil and grease. And that's one of the reasons why they're used in soaps and detergents and stuff. And the last cool property is that if you mix them together, they will give you salt and water, which is what we call the neutralization reaction.

6:55Remember, these definitions are still not complete. We still have to talk about their pH, which we'll do in the next video.