 When this red color solution mixes with this liquid, its color changes to blue and you might be wondering that, hey, what kind of magic is this? But no, this is just a chemical reaction. See, this red color solution is a litmus and when it comes in contact with the base, its color changes to blue. So let's talk more about litmus. So see, litmus is a dye, meaning a colored substance. We use dyes to color various things, like to color our food, to color our hair, and to even color clothes, right? So litmus is a dye and we derive this from lichens. Lichens, they are a combination of algae and fungus, okay? Don't worry about them. Basically, lichens are some organisms from which we derive this dye called litmus, which can change its color when it comes in contact with an acid or a base. And therefore, this can help us identify an acidic solution and a basic solution. Now you might be wondering, Ram, why do I need this? So see, so far we know that acids taste sour. For example, lemons or oranges, they both have acids in them and they taste sour. Whereas bases, they taste bitter. For example, bittergut or spinach or any green leafy vegetable, they all taste bitter and they all have bases in them. But see, we can't go around tasting each and every solution to identify for acid and bases. Because see, some acids and bases could be poisonous to us, harmful to us, right? So for this purpose, we cannot rely on taste itself. And that's why we use indicators. See indicators are compounds that indicate to us or tell us whether a given solution is acidic or basic. See, when an indicator comes in contact with an acid or a base, it will either change its color or it will change its smell to let us know. And you know, litmus is a type of indicator that changes its color. By the way, there are many more indicators apart from litmus also. But we will talk about them in a separate video. In this video, we are only going to talk about litmus indicator, okay? So now let's look at an experiment and see how litmus changes its color in the presence of acid and base. Now generally, you would find litmus solution to be available in two colors. One would be blue in color and it will be called blue litmus solution. And the other would be red in color. And that would be called red litmus solution. Now let's see how these change color. So here I have an acid in a container and I'm going to add a blue litmus solution to it. Okay? So you can see that slowly the color is changing to red, okay? This means that whenever an acid comes in contact with a blue litmus solution, the color changes to red. Means in case of an acid, the color will change from blue to red. Now here I have a base and I'm going to add a red litmus solution to it. Now you can see that slowly and slowly the color is changing to blue. That means when a base comes in contact with a red litmus, the color changes to blue. That means a base changes the color from red to blue. And this is how litmus helps us identify a solution as an acid or a base. Now imagine if you have an unknown solution and you want to find out what it is. So you put a blue litmus into it and you see the color is changing to red. That means it's for sure an acid because acid changes the color of blue litmus to red. And if you had put a red litmus and you saw that the color was changing to blue, then for sure you know that this is a base because base changes red litmus to blue. Okay, now you might be thinking, Ram, this is getting slightly complicated to remember. There are so many colors, blue to red and red to blue. How do I remember this? So see, for this purpose, I use the mnemonic B2B, meaning basis to blue or basis change the color from red to blue, okay? Or you can use the mnemonic BRB, meaning basis turn red to blue. And you know, once you remember the color change for base, the color change for acid is going to be just the opposite. If basis turn red to blue, then acids return blue to red. And I use this every time to find out what the color change is going to be. Okay, you might be wondering that Ram, acids turn blue litmus to red, okay? But what would happen if I add red litmus to acid? Will there be any color change? And if yes, then what will the color change to? So okay, why don't you pause the video and think about this yourself first? Now if you have tried it, let's see. See, acids turn the color of blue litmus to red. But if you add red litmus to it, the color will remain red. There would be no color change that you will notice over here. And similarly, basis turn the color of red litmus to blue. But if you add blue litmus to a base, then the color will remain blue. There would be no color change that you will notice over here also. Okay, to convince this to you, I have another experiment. See, lemons have acid in them. And we know that acids turn blue litmus to red. So when I add lemon juice to blue litmus, you can see that color is changing to red. But if I add the same lemon juice to a red litmus solution. See, the solution remains red. We cannot see any color change happening over here, right? So far we have seen how litmus changes its color when it comes in contact with an acid or a base. But what about solutions which are neither acidic nor basic? For example, water. See, water is a neutral solution. Can you guess what will be the color change of litmus when it comes in contact with water? Pause the video and take a guess. Now if you have tried it, let's see. So instead of telling you, let me just show you the experiment. So here I have two containers of water and I'm going to add litmus to each one of them. Okay. So first I'm adding red litmus to the first container and you can see that the color remains red. The color is not changing at all. Okay. Now let's try the same thing with blue litmus. I'm adding the blue one to the second container and you can see that the color remains same over here also. The color is not changing. Now this means that litmus when comes in contact with a neutral solution, it does not change its color. The red litmus will remain red and the blue litmus will remain blue in color. So far we have seen that acids turn blue litmus to red in color. And if you add red litmus to them, they will remain red in color. There will be no change happening. And on the opposite, bases turn red litmus to blue in color and if you add blue litmus to bases, they will remain blue in color. And there will be no color change that you will notice here. And if you have a neutral solution, then there will be no color change happening. If you add blue litmus to it, it will remain blue. And if you add red litmus to this, it will remain red. And how I like to remember this is by using the mnemonic B2B, bases turn to blue or BRB, bases turn red to blue. Okay, now with this, I would like to ask one question. I'm given that on adding blue litmus to a solution, no color change is observed. What can the solution be? Now the options are acid, base and neutral. So over here, I want you to pause the video and think about it and see this question is slightly tricky. So take your time. So, okay, now if you have tried it, let's see. So here we have been given that when we add blue litmus to the solution, there is no color change that we observe. So see, this solution can definitely be neutral because, you know, when you add blue litmus or red litmus to neutral, there is no color change that we see, right? But it can also be a base. See, we have seen that bases turn red litmus to blue. And if we add blue litmus to a base, then it remains blue. We do not see any color change happening over there. Same thing is happening over here. When we are adding blue litmus, we are seeing that it is remaining blue. There is no color change, right? So this solution can also be a base. So we cannot be sure that whether it is a base or a neutral solution. And to be sure, we will have to test this with a red litmus solution. Now imagine if red litmus solution, that also does not show any color change. That means for sure this solution is neutral. But if this changed from red to blue, that means definitely it is a base, not neutral, right? Now one last thing about litmus. See, some of you might have litmus paper in your lab instead of litmus solution. Basically it is just paper dipped in litmus solution. If you dip a paper in red litmus solution, you will get red litmus paper. And if you dip it in blue litmus solution, you will get blue litmus paper. You know, litmus paper are very handy and easy to carry. And that's why we often use litmus paper instead of litmus solution. But the chemical reactions and the color changes that happen are exactly the same. If you put a red litmus paper in a base, the color will change to blue. And if you put a blue litmus paper in an acid, the color will change to red. Now let's summarize the video. In this video, we saw that litmus is a type of indicator that indicates us the presence of acid or a base by changing its color. And it is generally available in two colors, red and blue. And you should remember that which litmus changes to what color when it comes in contact with acid and a base. And we also spoke about how to remember this by using the mnemonic B2B or BRB. And if you forgot about these things, don't worry. You can go back and watch the video and recall these things.