The Tollen's test is the reaction of aldehydes with silver(l) ions in basic solution to form silver metal and a carboxylate. 2 Ag+ + + 3 OH- - HR 2 Ag +_ W + 2 H2O ÃR Which species is being oxidized in the reaction? Choose... Which species is being reduced in the reaction? Choose... Which species is the visual indicator of a positive test? v Choose... Carboxylate ion Aldehyde Silver metal Water Silver(1) ion Hydroxide ion

Explanation:

When Tollen's test is done by aldehyde , silver ion is converted into silver which forms a layer which looks like a mirror.

Ag⁺ + e = Ag

It is a reduction process where silver(1) ion is reduced to metallic silver.

Aldehyde is oxidized to carboxylate ion.

CH₃CHO + 2 OH⁻ = CH₃COO⁻ + H₂O + H⁺ + 2e

Visual indicator is silver metal which forms silver mirror at the bottom of test tube .

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