A student is trying to determine the identity of some pieces of an unknown substance by finding their density. He finds the mass of a weighing boat to
be 2.69 g and the mass of the unknown pieces, including the weighing
boat, to be 18.01 g. To find the volume of the pieces, he measured out 25.7
mL of water in a graduated cylinder and then added the pieces to find a
new volume of 32.3 ml. What is the identity of the substance?
Density
2.16
Mineral
Halite
2.32
Gypsum
Quartz
2.65
2.72
Calcite
3.18
Fluorite
O halite
O quartz
O
O gypsum
fluorite

it is the most commonly accepted one

the answer is c

tell me if wrong

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