I have five beakers with some clear liquid and I'm going to pour a red colored liquid into all of them what do you think is going to happen to their colors well let's see whoa what did you notice oh wow they all had this different color changes but why to answer that question we need to introduce something called the ph and that's what we're going to do in this video now before we do that let's quickly recap what we already know about acids and bases we started thinking of acids as stuff that are sour and sticky but we got a little bit more rigorous then we realize that they are actually stuff that produce electrically charge hydrogen atoms in aquous Solutions and as a result they conduct electricity because there are charged particles in aquous solution and we also learned about their properties like they can corrode stones and metals what about bases we started thinking of them as something that is stuff that is bitter and slippery but then we realize hey they are the stuff that produce hydroxide in Aqua Solution and again because there are charged particles in Aqua Solution they're electrolytes they to conduct electricity and they have cool properties like they can break down oil and grease and that's one of the reasons why we use them in soaps and detergents but there's another cool property that we want to talk about and that is their pH so what exactly is pH well we can think of pH as a measure of how acidic or basic a given solution is to be more concrete it's actually a measure of the relative amount of the hydrogen plus that we find in a given solution or you can also say it's a measure of the concentration of this positively charge hydrogen atoms in a given solution okay so if it's highly concentrated we know that it's more acidic because acids tend to produce more H+ atoms isn't it and if it's less concentrated we know it's more basic and that's how measuring the pH will tell us how acidic or how basic a solution is in fact the word p the the letter P over here stands for power of hydrogen or potential of hydrogen so with this measure we can now build a pH scale and that scale runs from 0 to 14 a ph of 7 is neutral so you can imagine distilled water which is neither acidic nor basic but if the pH is below 7even you going towards increasing acidity so acids have a pH that is less than seven but wait a second more acidic means a higher concentration of H+ right so shouldn't that mean a higher pH this used to confuse me a lot because it turns out pH is an inverse scale more acidic more H+ means a lower pH that's just how we have built it okay so pH is an inverse scale and that's why lower the ph more acidic it is so acids have pH less than S on the other hand if the pH is more than seven we're going towards increasing alkalinity alkaline means basic okay so it's becoming more basic and therefore bases have a pH between 7 and 14 so here are our common examples on the pH scale another interesting thing over here is we know now something that has a pH of two for example is more acidic than something that has a ph3 isn't it but how much more well this is actually a logarithmic scale so it's 10 times more something that has more something has pH of 2 is 10 times more acidic than something that has ph3 and similarly something that has ph1 is 10 times more acidic than something that has pH to and so on and so forth okay we understand what PH is but how do we measure it well one of the ways to do that is by using something called the PH meters which are very similar to conductivity testers but instead of just testing for the presence of any ion pH meter specifically measure the relative amount of H+ ions by directly measuring the voltage so these are the most accurate devices you'll actually get a number you'll know exactly what the pH is but the problem is they're quite expensive so in our Labs we tend to use something else which we call pH indicators indicators change color based on again the relative amount of H+ or the concentration of H+ that's there in a solution a famous example is the litmus test we get something called litmus papers there red or blue these litmus papers are one of the simplest and the most accessible tool for pH testing it is made from naturally occurring compounds that are in living organisms known as lens these compounds change color based on the H+ concentration but they're very simple so the color is either red or blue red for acidic blue for basic for example the compounds in the red litmus paper are already in their acidic form so once you dip it in a solution if it stays red then the solution is either acidic or neutral but if it turns blue we know that the solution must be basic so let's see what happens when I dip over here hey it turned blue because it turned blue I know that this solution must be basic so look bases usually change colors to Blue and similarly the compounds in a blue litmus paper are already in their basic form so after dipping into a solution if it stays Blue we know that the solution must be basic or of course it can be neutral as well but after dipping if it turns red we know the solution must be acidic and let's see what's going to happen now and there you have it it turned red so we know that this solution over here must be an acid because acids turn blue litmus red in general we can think that acids turn things to Red in color we also have litmus Solutions with us so if you put red litmus and it turns blue look I know that that is a base and similarly if blue litmus gets turned to Red look I know that that is an acid but the LM must test can only tell you whether something is acidic or basic it doesn't tell you how acidic or how basic it is right for that we have something called the pH paper and Universal indicators these are more complex than a litmus paper because they are composed of many human-made components that each change color over a specific PH range so there will be a lot more color changes and based on the colors we can not only tell whether they're acidic or basic but we can also tell how acidic or how basic they are so let's look at a demo here is our pH paper here it comes there you go and now let's look at the color changes ooh what do we notice this is very reddish so I know this is very acidic this is orangish it's still acidic but I know that it is less acidic than this one this is greenish so it's somewhere close to neutral and then these are basic and similar to the pH papers we also have Universal indicators and this is what we saw at the beginning of the video again let's have a look and let's see the color changes ooho beautiful isn't it again we can see that these are very acidic this one is yellowish which means it's also acidic but it's less acidic than these one uh these two and then we have very basic Solutions over here finally we can go back and complete our definition of acids and bases acids are substances that produce H+ in Aqua Solution and have a pH Which is less than seven and turn blue litmus paper red what about bases well they are the substances that produce o minus hydroxide in Aquis solution and they have a pH which is more than seven and turn red litmus paper blue all right putting it all together we learned that pH is a measure of the relative amount of H+ in a solution or you can think of it as a measure of the concentration of H+ in your solution when the pH is less than seven it is acidic and if the pH is more than seven it is basic and how do we measure the pH well we can use PH meters but they are quite expensive but a much more cost- effective and fun way is by using pH into indicators we have litmus test which are quite limited because they only tell you whether something is athetic or basic and then we have pH papers and Universal indicators which also tell you how acidic or how basic something is