A pure sample of a monoprotic acid is dissolved in water. the sample is titrated with sodium hydroxide solution. at the point where 20.0 ml of the naoh solution has been added, the ph is 4.15. the phenolphthalein endpoint of the titration is observed when 50.0 ml of naoh have been added. what is the pka of the acid

i'm wiling to try and you : )

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

d) a person who learns about the world by observing it.

explanation:

scientist are people who discover why and how things are done and made in the world.