experiment help (1 Viewer)

[starbuckscoffee]

In an experiment to examine the breakdown of starch by dilute hydrochloric acid and by an enzyme; we added iodine to the starch and HCl solution, then sodium hydroxide, before we added the benedict reagent.

Why did the solution of starch and HCl have to be neutralised with sodium hydroxide before we added the benedict reagent to test for gucose and maltose?

 

[Undermyskin]

This is BIOLOGY! or it's not in Production of Materials!

 

[Forbidden.]

This is BIOLOGY! or it's not in Production of Materials!

Because the thread starter maybe is trying to find better opportunity in another branch of science.
It's like Chemists consulting Physicists.

 

[brenton1987]

Why did the solution of starch and HCl have to be neutralised with sodium hydroxide before we added the benedict reagent to test for gucose and maltose?

Benedict's Solution contains copper (II) sulfate which is reduced to copper (I) oxide by the reducing sugars.

Cu(I) oxide dissolves in HCl to form HCuCl₂. This would result in a negative test.
In alkaline solution the Cu(I) oxide forms a red precipitate which indicates a positive test.

 

[cameron0110]

Based on the ever reliable Wikipedia I'm guessing its a combination of the solubility/reactivity of Cu2O (which will react with HCl to give soluble CuCl if HCl is still around) and the fact that base is actually required for the reduction of Cu(II) to Cu(I) by the sugar. So if HCl was still in solution then Benedict's reagent will just neutralise the HCl rather than creating basic conditions.