this is a part two of topic six in this part we will explore a stay and base dissociation constants ka and Kb but what is the acid dissociation constant actually acid dissociation constant ka is used to identify how much SE molecules have dissociated in the water solution okay here we use H n to represent one acid so you play a G in water what happened well dissociate some h+ protons and also anions a minus here then we can use the equation ka equals to concentration of the protons times concentration of a minus over the concentration of the h a to calculate how much as you have dissociate in the water right then we also know the larger the value of the K in the stronger domestic the smaller the value of K is a weak acid that looks like very straightforward but here I will give you two sets of data and can you choose one set of data to calculate K that means we need to use the initial data or final data for example the concentration of the h plus we need put zero and zero over 100 we need to use a final data and put here is 0.2 0.2 and 0.8 so which one the travel of course the second set of data incredible so when we calculate the KA we must use the concentration at equilibrium means final data okay let's do some exercise here question one write a simple dissociation reaction and ka expression for each of the as it's a nitrous sa B as the SE C phosphoric acid question - which of the three acids is the weakest acid it looks like very simple right you can try it first and I will explain in the next slide but here I need to identify something here I see the ka1 for phosphoric acid what's a ka1 means you notice the phosphoric SC got three protons here that means the phosphor SE can donate first proton second proton at the bottom so the KA one means what the phosphoric acid doneita first proton at the time the acid dissociation constant equal to K ay 1 [Music] okay let's answer the question first one first nitrous acid so all the acid here we consider as we s it so we use half arrow here can you write down the expression for the nitrous and see it's quite easy right you just write on ka equals 2 concentration of the h plus times concentration of no.2 - over concentration of nitric acid right it's just like that the second one party is 1 as the si este ese also symbolic ka equal to plus times concentration - over concentration of esthetic right captain then the last one patsy phosphoric NC also seen but phosphoric acid got three protons so we just don't need the first proton so we just write down the K a one right the first proton the equal to concentration of the proton concentration of P alpha minus over concentration of so it's quite simple right just like that but some student will ask question why the phosphor is the only donate the first proton well the explanation is here although the phosphorus a voluntary protons but the extent of the association for the first proton is larger then the second one inter 1 that means the first one they're easier to donate the second one and the third one is the path that's why we only write the first day okay how about the question to which SC is a weakest acid with this s it need to compare the K value the smaller K value means what so we go si right so which one is smaller smallest okay which one st si right so the weakest si is a lower scale value still se so ka value for s the si equal to one point eight times 10 to power a negative one maybe you need to memorize a KA value for the STS is quite important 1.8 times 10 to power of negative five okay in this page we talked about the base dissociation constant KB then you can see we use B to represent one base so you put a base into whatever happen because the base is proton acceptor so we are one program and phone this one and also released h- my dad how to write an equation for the base dissociation constant KB yes we pay be the equal to the concentration or the BH plus and the concentration of the o h- over the concentration of the B but some student will ask hey why not put a concentration of the water here why not actually no need because you can see out here the a question equals equals equals right but only this critical status of the water is a liquid so that means so we got a lot water here so we just can solve the concentration of the water here no need for the water here okay yeah it's quite simple right then the larger the value of the K be the stronger the base the smaller the value of the K be the winter base actually same an acid okay let's do one example write down the KB expression of a weak base HC or minus some Susan will ask yeah just one in the form a ion right why the form a ion is a base yes actually for me I own its base why you consider your a bronsted-lowry theory what is the base what a definition of the base the base is a proton acceptor oh yeah proton acceptor so you put the for me I don't you what do I happen you can see for me ion can take one proton from water in general formic acid so in this case the formic ion is a base right so can you write down the KP expression for the forming I am of course yes so KB will equal to the concentration of the formic acid times concentration of O H minus over concentration of the form AI ops a double water here I already mentioned in the previous slide okay let's take a look the last concept in this path ion product constant kW do you think water is a co base have a think about this question you can see that statement here water can be an acid or a base right so we call water h2o is amphoteric amphoteric so if you put a water into whatever happen the water also will dissociate into the same amount of the hydrogen ions and have your science and scientists give a ion product constant kW this equation will equal to the concentration of the protons times concentration of O h- right and at 25 degrees this value of equal to 1.0 times 10 to power of negative 14 okay now answer my question if the pH value equal to 7 how about the concentration of the proton and hop out the concentration of the h - Skyy simple right the concentration of the proton equal to 1.0 times 10 to power of negative 7 right then concentration of the Oh H - also equal to 1.0 times 10 to power of negative 7 so x is 2 together equals to negative 14 we can use the kW to identify whether the solution is sed basic or neutral how to identify I will give you the three criteria here if the concentration of the protons equals to the concentration of the oil - this is a neutral social if the concentration of the proton larger than concentration of the oil - this is an acidic solution and if the concentration on proton smaller than concentration of H - this is a basic solution so we can use the three criteria to identify the solution is acidic basic or neutral ok let's do the final example question calculate the concentration of the proton or concentration of hydroxide ions as required for each of the four instructions at 25 degrees and a state whether the solution is a neutral as DMB C and C the question is okay remember the question kW KW l equals 2 concentration of the h plus times concentration of O h- and equal to 1.0 times 10 to power of negative 14 and 25 degrees right in a question a we know the concentration of oil - is one point zero times ten to power a negative five so how do you calculate concentration of the hydrogen ions concentration hydrogen ions will be close to one point zero times 10 to power of negative 14 over one point zero times 10 to power of negative five so answer will be 1 point zero times 10 to power negative 9 so in the question 8 which one is a higher concentration is higher or H - or protons actually is hydroxide right so how's your outside concentration is larger than concentration of the proton so the solution will be acidic or basic yeah basic basic this is a question hey how about a question B question boring yeah actually the concentration of the proton will equal to the concentration of the OS - and equal to 1.0 times 10 to power of negative seven so a tree solution B is neutral yes new track so just the end of the part two of topic six