4. The pH of an aqueous solution is determined to be 1.50. Calculate the hydronium ion concentration.
b. Calculate the hydroxide ion concentration.

-lg[H+]=1.5

which means that [H+]=0.03M

pOH=14-pH=14-1.5=12.5

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