How many grams of Sulfur are there in 2.05 x 10^25 molecules of Calcium Sulfate?

1090 grams Sulfur (3 sig-figs)

Explanation:

Given 2.05 x 10²⁵ molecules CaSO₄ => 2.05 x 10²⁵ Sulfur atoms (subscript = 1 mole).

Converting 2.05 x 10²⁵ sulfur atoms to moles, divide by Avogadro's Number

(= 6.023 x 10²³ sulfur atoms / mole sulfur) => 2.05 x 10²⁵ sulfur atoms/6.023 x 10²³ sulfur atoms/mole sulfur atoms = 34.036 moles sulfur atoms.

Converting 34.036 moles sulfur to grams sulfur multiply by formula wt. of sulfur (=32g/mole S)

=> 34.036moles S x 32g/mole S = 1089.158 grams S ≅ 1090 g S (3 sig-figs)

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