During the % By Mass of Sugar in Soda Lab a group found the mass of soda used was 40.0 grams.
After all the water was evaporated, what was left in the evaporating dish weighed 5.0 grams. The
mass of the water would be
A.. unable to be calculated
B... 40.0 grams
C... 35.0 grams
D... 45.0 grams

the answer is na (sodium)

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