A solution contains 0.0280 m pb2 (aq and 0.0280 m sr2 (aq. if we add so42–(aq, what will be the concentration of pb2 (aq when srso4(s begins to precipitate?

well in order to answer this question you have to provide more information < 3

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