10. Benedict’s Test & Lactase-Catalyzed Lactose Hydrolysis

all answers r A rn, redo placement later, or remove MQ idk.

What does a positive Benedict's test indicate?

Reducing substances capable of reducing Cu(II) under the test conditions

What is reduced during a positive Benedict's reaction?

Cu(II) to Cu(I)

What visible change is associated with a positive Benedict's test?

Blue solution changes toward green/yellow/orange/red with precipitate

Why can glucose give a positive Benedict's test?

Its open-chain form has a reactive aldehyde that can reduce copper(II)

Why is sucrose normally negative in Benedict's test?

Both anomeric carbons are involved in the glycosidic linkage, leaving no free reducing end

Why can fructose, a ketose, still test positive?

Under alkaline conditions it can isomerize through an enediol intermediate to aldose forms

What is the overall reaction catalyzed by lactase on lactose?

Lactose + water → glucose + galactose

Why should lactose treated with lactase produce a positive Benedict's result?

Hydrolysis produces glucose and galactose, both reducing sugars

In the report, which tested carbohydrate remained blue with no precipitate?

Sucrose

Which set of samples gave positive precipitate results in the report?

Glucose, galactose, fructose, lactose, maltose, and lactose + lactase

Why did the report's Benedict's results not quantify how much lactose was hydrolyzed?

Both untreated lactose and lactose-plus-lactase tested positive

What is the role of heating in Benedict's test?

It promotes the redox reaction between reducing sugars and copper(II)

Which protocol sequence matches the report's carbohydrate test?

Prepare sugar solution; add lactase to the lactose treatment; wait 5 min; add Benedict's reagent; heat 10–15 min

How would you teach the copper-redox chemistry with a simple electron-transfer explanation?

The sugar donates electrons; Cu(II) accepts electrons and is reduced to Cu(I)

Why is the color shade not a precise measure of sugar concentration in this report?

Heating time and reaction conditions differed, and the test was used qualitatively

If a student forgets to add Benedict's reagent but heats the sugar solution, what is the main problem?

The copper reagent needed for the characteristic redox/precipitate reaction is absent

What is a useful negative comparison for Benedict's testing in this experiment?

Sucrose, which remained blue

Which is the best way to test whether lactase caused an increase in reducing sugars?

Compare matched lactose samples with and without active lactase under the same timing and conditions

What is the enzyme's role in the reaction mechanism?

It lowers activation energy and facilitates glycosidic bond hydrolysis without being consumed overall