Portland uses sodium hydroxide (NaOH) to increase the pH of its drinking water to 8.0 as a method of lead corrosion control in their water distribution pipes. At high pH values, lead will form lead hydroxides (Pb(OH)2(s)). What concentration of Pb2 is expected to be found in the drinking water supply if lead pipes/fixtures are present (assume equilibrium conditions)

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