today i'm going to explain first part of further aspects of equilibria kw is dynamic product of water the value of kw varies with temperature at room temperature this is equal to 1 times 10 to the power of minus 14 mole squared dn minus 6. let's talk about this in more detail kw actually derived from kc expression as you already know water dissociate into h plus and the h minus ions we can write this in kc expression the important point here is that equilibria lies well to the left because water is very weak at dissociating therefore we can assume that concentration of water is almost constant by removing constants we can then express k february let's move on to ph calculations ph is defined as the negative logarithm to the base 10 of the hydrogen ion concentration in simple this is written as hydrogen ion concentration is equal to the 10 to the power of minus ph we can use these two equations to convert from ph to h plus concentration and from h concentration to ph let's solve practice question first calculate the ph of a solution whose h plus ion concentration is 5.32 times 10 to the power of minus 4 mole per cubic decimeter first write down the ph equation and then put h plus ion concentration into the equation use your calculator to find the answer let's solve practice question calculate the hydrogen ion concentration of a solution whose ph is 10.5 first write down the h plus ion concentration equation and then put ph into the equation use your calculator to find the final answer now let's solve saq 1 and 2. these are the answers for scq-1 and 2. now let's move on to ph calculations ph of strong acids strong acids completely dissociate in solution so concentration of h plus ion is equal to concentration of acid this means ph can easily be calculated by using this equation ph of strong bases to work out the ph of a strong base you have to follow these steps first calculate the concentration of hydroxide ions second calculate the concentration of h plus science using cape febria last convert h plus concentration into ph using this equation calculate the ph of a solution of sodium hydroxide of concentration of 0.05 mole per cubic decimeter since the concentration of hydroxide ion is already given we can use kw to find the concentration of h plus ion then we can put h plus sine concentration to the ph equation to find the final answer ph let's solve saq3 these are the final answers now let's move on to ka as a dissociation constant it is the equilibrium constant for a weak acid we can express it like this the lower the ka value the lower the concentration of h plus ion and an ion so farther left of equilibrium lies in other words the lower decay value the recurrent ionization for weak acids the key is very small so ka values can be converted into pka values using the equation below as pka increases the strength of the acid decreases calculate the ph of 0.1 mol per cubic decimeter ethanoic acid in this question ka is already given first write down the general equation involving the association of ethanoic acid and then write down the acid dissociation constant from this expression you can calculate a hydrogen ion concentration put k value and concentration of acid into the equation and use your calculator to find the h plus ion concentration then put h plus sine concentration into the ph equation and use your calculator to find the final answer let's solve saq456 this are the answers let's move on to indicator indicator is a weak acid that changes color when it donates a proton we can draw a titration curve to show how ph changes during an acid-base titration titration curves are used to select appropriate indicators for acid-base titrations the important point is that the indicator must change color on the vertical section of the graph in other words the indicator must change color within the end point of titration for example if we draw a strong acid strong base titration graph there is a sharp fall in the graph line between page 10.5 and page 3.5 a midpoint of the sleep slope is at ph 7. bromothymol indicator changes color within the end point of titration so it is appropriate indicator beside from strong base strong acid titration graph we can draw titration graphs of strong base weak acid or weak base strong acid or a weak base weak acid how to distinguish different kinds of grafts if you look at this graph as highest ph is at ph 11 and the lowest ph is at page 1 you can find easily that this is weak based strong acid titration graph also by looking at weak acid wick based titration graph we can find out that there is no sharp fall in the graph line therefore no acid base indicator is suitable to determine the endpoint of this fraction now let's solve saq728 these are the answers