• Congratulations to the Class of 2024 on your results!
    Let us know how you went here
    Got a question about your uni preferences? Ask us here

experiment help (1 Viewer)

Joined
Nov 25, 2007
Messages
30
Gender
Female
HSC
2009
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

Self-delusive
Joined
Dec 9, 2007
Messages
587
Gender
Male
HSC
2008
This is BIOLOGY! or it's not in Production of Materials!
 
Last edited:

brenton1987

Member
Joined
Jun 9, 2004
Messages
249
Gender
Undisclosed
HSC
N/A
starbuckscoffee said:
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

Member
Joined
Mar 23, 2004
Messages
113
Gender
Male
HSC
2004
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.
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top