A student would like to prepare a 0.010 M solution from a 1.0 M stock solution with minimal error. The student can choose to do a one-step dilution that uses a 10-mL transfer pipet and a 1000-mL volumetric flask or a two-step dilution using a 50-mL pipet and a 1000-mL volumetric flask for the first dilution, and a 100-mL pipet and a 500-mL volumetric flask for the second dilution. Which method has the smallest overall relative uncertainty and what is the value

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