Class 7 Science Practical | Indicators (Acid, Base & Neutral) | Litmus Test | NCERT

[00:00:02]acid and dropping uh little bit of hydrochloric acid in the watch glass.

[00:00:29]The same experiment activity one blue litmus. Okay.

[00:00:40]Blue litus paper an indicator a natural indicator derived from lichon.

[00:00:48]What it looks like?

[00:00:51]You can easily see over here.

[00:00:56]It's the blue litmos.

[00:00:59]Just I'm dipping it over it. And see the effect what happens as I dip it.

[00:01:10]It's it has become red.

[00:01:15]You can see the same experiment.

[00:01:18]>> Activity number one.

[00:01:21]This activity number one discusses how we can use indicator to test if a sample is acidic or not. Suppose I take another and I'm just putting water over here and let's see if it has any effect on the lit paper or not.

[00:02:02]Is there any effect?

[00:02:04]>> It means that water is not acidic in nature. Water is neutral. Okay.

[00:02:12]Now look at the second one. Take some soap solution in a petri dish and we will See what happened.

[00:02:23]Soap is basic in nature. So now we will use any base. We have many bases over here. We can take a sodium hydroxide. You can see any bases over there.

[00:02:42]And we can see what happens if we deep it has become red. We can use this one also. Okay.

[00:02:53]It will change the red to again to blue.

[00:02:58]If I see it is red paper.

[00:03:13]>> Yes sir.

[00:03:15]>> Just I'm putting the base over here and what will happen?

[00:03:19]Reaction has started happening. You can see the red again turn into >> blue.

[00:03:30]Actually all the bases contain hydroxide ions and this litmus this red lumus turns into blue in presence of a base. So acid turns blue litmus to red basis turns red lmas to blue. This is your activity one and activity two of your prescribed textbook. There are many other indicators. We have phenopylene. If phenopylene is there in acidic solution no color change will be there but in the basic solution it will turn to pink. We can see this with the elevator.

[00:04:28]So suppose I put some hydrochloric acid over here in this watch glass.

[00:04:39]What will happen actually?

[00:04:46]Nothing will happen.

[00:04:50]It remains colorless. No change in the color is there. Okay.

[00:04:55]If you have can see some u whitish part that is only due to the impurities.

[00:05:01]But phenopylene does not cause any change in cases of bases. The colorless acid remains colorless.

[00:05:13]But you will see a spectacle when I put the base in it. You will like it.

[00:05:23]I'm putting the base over here.

[00:05:26]Okay. Now what happens if I put a phenopillene into it?

[00:05:37]>> Yes, just a drop of it is uh enough to change it into pink. If we have any solution given to us and it changes into pink that means we have a base a basic solution. Okay. What is a base? Base are generally slippery to touch, soapy to fill and they give hydroxide ions on dissociation. What are acids? Acids are sour in taste.

[00:06:07]But don't taste mineral acids.

[00:06:10]Okay? Only the organic one, the citric acid, the tartic acid, the oxylic acids, not the mineral acid, >> hydrochloric acid, mineral acid. You cannot taste it.

[00:06:20]>> It is a very very strong acid. It will burn your tongue. It will burn your taste words. Okay. So, two indicators we have seen litmus blue litmus will change to red in acidic solution. Red litmus will change to blue in basic solution.

[00:06:40]Phenof indicator it will remain colorless in acidic solution and it will turn to pink in basic solution.

[00:06:55]This is all about indicators. Over here we have used two indicators. You like the experiment?

[00:07:00]>> It's a demonstration what you are reading in the book. You can draw the diagrams based