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## Strength of acid and base

# pH change & the concentration of H+/OH-

## Video transcript

let's solve some problems on how change in concentration of H+ and OH h minus sign changes the pH of the solution and even vice versa so here is my first problem when acid rain mixes with the river water the concentration of H+ ion increases so it's given to us that the concentration of H+ ion this is increasing when the concentration of H+ ion increases pH of the river water - meaning what is happening to the pH of the river water if the concentration of H+ ions is increasing okay we know that if a solution has excess of h+ ions that means is acetic and if the concentration of h+ science is increasing meaning the amount of h+ ions in the solution is increasing that means the solution is becoming more acidic see the acidic nature of the solution depends on the concentration of h+ ions if more concentration of h+ ions then more acetic is the solution just like if in a suger solution the concentration of sugar that increased that means it's more sweet now right so here also i will say since the concentration of H+ ion is increasing it is becoming more acidic more acetic now let's see that if a solution becomes more acidic how does this pH change so can you pause the video and think about this by yourself first okay now that you have thought about it let's see so for this I'm going to bring back my pH scale okay over here I can see that a pH of 7 means the solution is neutral and a pH less than 7 means it's acidic and a pH of zero this means the most acidic solution so from this I can understand that the lesser the pH number the more acidic is this solution right and here in our example the solution is becoming more acidic that means its pH number should have reduced so my answer will be that pH is reducing or pH is decreasing decreasing okay now let's solve one more problem so this time I'm given in the lab Harry prepares an energy drink by mixing two unknown solutions during the reaction he notices an increase of Oh H - iron concentration okay that means that concentration of Oh H - iron this is increasing when the concentration of Oh H - iron increases pH value so we have to find out if the concentration of Oh H - ion increases what will happen to the value of pH of the solution will it increase or will it decrease now can you pause this video and try to solve this by yourself first now if you have tried it let's see so I know that if there are excess of H - iron present that means the solution is basic in nature and if the concentration of O H minus ion this increases meaning there are more and more amount of which - iron present in the same amount of liquid that means it is even more basic it is becoming more and more basic right so concentration of H - iron increases the solution becomes more basic more basic now what do you think will happen to the pH of this solution which is becoming more basic will it increase or will it decrease so for this let's bring back our pH scale so this shows that pH of 7 is neutral and a pH greater than 7 means basic solution and a pH of 14 this means it is most basic solution so from this I can understand that if the pH value this increases that means the solution is becoming more and more basic so here our solution is becoming more and more basic that means is pH value should be increasing so my answer is going to be here the pH value increases okay with this less all one last problem so we are given that for a class project Seeta collects a sample of soil from a backyard on adding some solution to it she finds that the pH of the soil increases from 8 to 10 that means pH of soil is increasing from 8 to 10 when creating creases from 8 to 10 the concentration of O h minus ion so we have to tell what is happening to the concentration of O h minus ion okay so can you pause the video and try to solve this by yourself first now if you have tried it let's see so given that initially original pH was 8 right what does this mean so let me bring back my pH scale so here we can see that 7 means a neutral pH and any pH greater than 7 means a basic solution so over here our initial solution had a pH of 8 that means our solution was basic in nature right and we see that pH is increasing what does this mean so we can see that here pH of 14 is most basic that means I can say that as the pH increases as the pH value increases the solution becomes more and more basic so that means our solution of soil is becoming more basic over here so that means the solution is becoming more basic right pH is increasing and solution is becoming more basic now based on this what can we say about the concentration of O h minus ion so see we know that basic solutions they have excess of h minus ion but if a solution is becoming more basic that means the amount of h minus ion is increasing in the solution the concentration of voice - ein should be increasing in the solution this should be increasing in the solution because the basic nature is dependent on the concentration the more the concentration of watch- the more basic the solution is so my answer over here is going to be increasing increasing so as pH increases the solution becomes more basic and the concentration of H - size increases