okay the last thing we're going to talk about in chapter 3 is acids bases pH and buffers okay so if we take a look at the water in my water cup usually I have my water bottle today next to me I have a nice little Elsa and Anna cup filled with water if we take a look at all the water molecules in that cup of water they don't all necessarily at one time exist as water the way we know it or h2o what can happen on occasion is that water molecules can sort of dissociate so a hydrogen atom in a hydrogen bond between two water molecules can actually shift from one water molecule to another and I've shown this at the bottom of this particular slide right here so here we have two water molecules here's one right there second one right there this is the nice little hydrogen question so this hydrogen is going to be hydrogen bonded to this electronegative oxygen on the left hand side on occasion that hydrogen atom can sort of leave its electron behind remember let's review a hydrogen atom exists essentially as one proton and one electron right one proton one electron there are no for the most part in most of the hydrogen atoms there are no neutrons in the atomic nucleus we have one proton and one electron so the two are going to separate and the hydrogen atom is going to leave its electron behind and it's going to be transferred simply as an individual proton or what we call a hydrogen ion symbolizes H+ because it's lost one electron so it's lost that one negative charge it becomes slightly positively charged it's a Charged particle so we call it an ion so it's a hydrogen ion H+ it leaves its electron behind and it goes and it attaches itself to that other water molecule with which it was originally hydrogen bonded so the molecule that gained that one extra proton is called the hydronium ion or h3o+ and then the molecule that lost that proton it's going to be called our hydroxide ion the electron that was left behind St stays there so the hydroxide ion has a negative charge okay often times though this is kind of complicated and as biologists we want to keep things sort of simple so one way to abbreviate this particular reaction that I've shown you guys at the bottom of this slide is simply to say that one water molecule or h2o is going to dissociate into a proton or an H+ a hydrogen ion and the hydroxide ion sort of taking out one water molecule on both sides of the chemical reaction just to make things simple but keep in mind that this hydrogen ion H+ doesn't actually exist by itself it's going to be attached to that other water molecule forming that hydronium ion we just ignore that other water molecule and consider it just an H+ on this side all right so now that we've established that water is essentially in this uh of dynamic equilibrium in which water molecules are going to dissociate at the same rate at which they are being formed and actually the number of water molecules that is dissociated at any given time in a body of water is tetiny Tiny it's like one in 500 million so most of them exist as normal water molecules but you will have one on accasion one water molecule that dissociates into a hydroxide ion and a hydrogen so statistically very very rare but this rate of dissociation of these water molecules has a great effect on organisms and so the changes in concentrations of both the hydrogen ion and the hydroxide ion can D can D can drastically affect the chemistry of a cell it's kind of like a nice little balance so usually I use my hands in lecture but today I've made myself a nice little teeter totter here on one side we have our hydrogen ion the other side we have our hydroxide ion anytime that you see these ions with the brackets around them that essentially means molar concentration so this is showing you the concentration of hydrogen ions and this is the concentration of hydroxide ions in life there has to be a nice little balance between these two and there are different things that can shift this balance and can affect that balance that's what we're going to talk about next if we take a look at pure water in pure water the concentrations of hydrogen ions and hydroxide ions are going to be equal right and this is essentially what we have when we have a neutral solution pure water is going to be neutral so we look at the bottom of this particular slide down here in that middle Beaker we have equal concentrations of the hydrogen ion and the hydroxide ion this is neutral when you add certain solutes that are either called acids or bases to Pure Water you can shift this balance one way or another so modifying or adding these certain solutes which are called acids and bases can modify these concentrations of hydrogen ions and hydroxide ions and as biologists chemists also we use something called the pH scale to describe whether a solution is going to be either acidic or basic right if you have a basic solution as we have in the beaker on the left in a basic solution your hydrogen ion concentration is going to be really low and because there is this inverse relationship between between let's see where to put this um between the hydrogen ions and hydroxide ions if you are going to decrease the hydrogen ionic concentration that is naturally going to increase the hydroxide ion concentration that's for basic solution now if you have an acidic solution essentially does the opposite you're going to tilt your little teeter totter this way and an acidic solution your hydrogen ion concentration is going to be very high respectively in verely your hydroxide ion concentration is going to be really low all right so an acid is going to be any substance that's going to increase our hydrogen ion concentration and a base is going to be the opposite there any substance that's going to reduce the hydrogen ion concentration of a solution it reduces the hydrogen ion concentration naturally it's going to increase the hydroxide ion concentration all right so let's talk a little bit about about this pH scale gets a little bit complicated so in any aquous solution at 25° C the product or multiplying the hydrogen ion concentration hydroxide ion concentration is always going to be constant and can be written as 104 so that means that the hydrogen ion concentration times the hydroxide ion concentration must equal 10 -14 for example in pure water right again our teeter totter is going to be perfectly balanced so these two concentrations must be equal to get these two concentrations equal and they must equal 104 under standard conditions hydrogen ion concentration must be 10^7 hydroxide ion concentration must be 10 to the -7 they have to be equal balanced now when we say hey this is the p of this particular solution that can be defined as the negative logarithm of the hydrogen ion concentration we're talking about pH even though there's an inverse relationship between the two pH is only concerned with the hydrogen ion concentration all right so we can write the pH two different ways the pH is either going to be the negative log of the hydrogen ion concentration that can be tricky to think about if math isn't quite your thing an easier way to look at is if you know the hydrogen ion concentration right you know that that equals 10 the something that exponent is automatically going to give you the pH as you see written here on the right so going back to our example of a neutral solution in a neutral solution hydrogen ion concentration was going to be 107 and it has to equal the hydroxide ion concentration also 107 so if we know in a neutral solution our hydrogen ion concentration is 10 the7 hydrogen ion concentration here is going to be 10 to the -7 and if this exponent gives us the pH we know then that the pH has to be a pH of seven and that is in fact true any solutions that are acidic are going to have pH values that are less than seven right acidic remember High hydrogen ion concentration basic Solutions are going to have pH values that are greater than seven and are going to have a low hydrogen ion concentration most biological fluids have a pH value somewhere between 6 and 8 right around neutral right around that level teeter totter where both concentrations are equal of the hydrogen ion and the hydroxide ion all right here's an example of what the pH scale looks like so it goes all the way from 0 to 14 any acidic solution is going to have a low PH kind of tricky to think about right CU again pH talks about the hydrogen ion concentration in acidic solution hydrogen ion concentration is going to be high but the pH number on the pH scale is going to be low so things like battery acid lemon juice these have a very low PH 1 2 3 Etc but they have high hydrogen ion concentration when you get to neutral right balance between hydrogen hydroxide ions that's a pH of seven it's going to be pure water and most biological uh Solutions and then if you tip the scale the other way you decrease your hydrogen ion concentration you increase your hydroxide ion concentration and you get to those high phes and these Solutions are going to be basic things like ammonia and bleach are very very basic okay one more thing to note on this pH scale so the concentration of these hydrogen and hydroxide ions can vary greatly in a variety of different solutions right there's a huge scale and we sort of shrink the scale together so that we're not dealing with really large numbers and instead we're just going from 0 to 14 thing to keep in mind that this is a logarithmic scale right on the previous two slides ago we talked about logarithms right and this logarithm is base 10 10 to whatever exponent we're talking about that means if this is a the pH scale is in a logarithmic scale base 10 that means that between each pH value there's a tfold difference in our hydrogen ion concentration so for example pH of 6 right here has 10 times more hydrogen ions than a ph of 7 also pH of 13 has a thousand times less hydrogen ions than a pH of 10 so for each time you switch between one of these values on a pH scale that's a 10-fold change so 10 * 10 * 10 gives you a th000 okay there are certain solutions that sort of help to maintain a certain pH and prevent huge fluctuations in the pH of things like the blood for example the internal pH of most living cells must remain close to that neutral value of seven and so many things like your bloodstream are going to have substances in there that act as buffers or buffer is going to be any substance that minimizes changes in the concentrations of the hydrogen and the hydroxide ion in solution so even if you were to add a strong acid or a strong base the buffer in that solution would prevent this teeter totter from growing crazy and it might just fluctuate a little bit around that level point or wherever the pH of that solution started most buffer Solutions contain a weak acid and its corresponding base which can combine reversibly with hydrogen ions okay so if all of a sudden the cell is exposed to high hydrogen ion concentrations the buffers are going to absorb those to sort of neutralize the solution or if an uh a base is added and the hydrogen ion concentration is drastically decreased the buffers are going to add some more hydrogen ions to that solution again to minimize any really really drastic fluctuations