BENEDICT’S TEST

Benedict’s test (A) Sugar Tests

This is a chemical reagent named after an American chemist, Stanley Rossiter

Benedict.

This is a test to detect reducing sugars in a solution via oxidation reduction

reaction.

A reducing sugar is a carbohydrate possessing either a free aldehyde or free

ketone functional group as part of its molecular structure

Reducing sugars are oxidized by the copper ion in solution to form a carboxylic

acid and reddish precipitate of copper (I) oxide.

Since they reduce the Cu2+ Cu+ - the function of this reagent is to oxidize the

presence of the aldehyde - ketone group in a sugar solution.

Like the Fehling’s test, a positive result is indicated by the formation of brick

red precipitate.

The composition of this reagent is copper sulfate in alkaline citrate.

Here’s the chemical equation that would be present in the reaction:

Would be responsible for the brick red precipitate.

Specific objective: To detect the presence of reducing sugars through a visible positive

result of formation of brick red precipitate from each samples.

* Color of reagent: Blue

Samples Observations

Glucose Red- Orange precipitate

Sucrose Blue solution

Lactose Red – orange precipitate

a. Glucose

Benedict solution is light blue because it contains copper sulfate. When it is mixed

and heated with a sugar, such as glucose, which has electrons available to donate, the

copper will accept the electrons and become reduced, which turns it to brick red. During

this process, the blue copper (II) ion is reduced to a red copper (I) ion. While the copper

is being reduced, the glucose gives up an electron and is oxidized. Because glucose is

able to reduce the copper in Benedict solution, we call it a reducing sugar.

b. Sucrose

Sucrose is a disaccharide derived from glucose and fructose. It has a molecular

formula of

C12H22O11.

Because of glycosidic linkage, there is no presence of free aldehyde, which is a

property of a reducing sugar. This makes sucrose a non-reducing sugar, thus having no

reaction with the

Benedict’s reagent. However, a non-reducing sugar can be hydrolyzed using

dilute hydrochloric acid to convert the acetal or ketal into a hemiacetal or hemiketal.

After hydrolysis and neutralization of the acid, the product may be a reducing sugar that

gives normal reactions with the test solutions.

c. Fructose

Fructose is a 6-carbon polyhydroxy ketone. It is an isomer of glucose, therefore

they both have the same molecular formula (C6H12O6) but they differ structurally.

Glycosidic linkage

between C1 of glucose and C2 of fructose

These Disaccharide sugar contains two sugars that contain both aldehyde and a ketone

as their first carbon.

The ketone here undergoes Tautomerism which means that the ketone functional

group hydrolyzes first into an aldehyde and formed aldose. This makes the possibility

to react the sugar in the Benedict’s reagent. And this property only happens to an alpha

– hydroxy ketone.

Benedicts Test (B) – Test for urine samples

To test in the urine samples on their glucose concentration.

The reagent would oxidize the reducing sugars and determine their glucose

concentration as the table shows:

  0  *Blue  None  <0.1% or <100 mg/dL

  +  Green  Some  0.5% or 150 mg/dL

  ++  Yellow  More  1.0% or 1000 mg/dL

  +++  Orange  Much  2.0% or 200 mg/dL

. . . . . . . ++++  Red  Most >2.0% or >2000

mg/dL

Color Symbol Description Amount of Amylase Activity  Glucose

Concentration

  * blue = 0 (no precipitate; no color change) 

The different color would be observed as how much the concentration of the

urine sample tested.

Would form a white precipitate, indication that sugars are present in the urine

tested.

It is determined by their amount of Amylase activity containing AMYLOSE - a

glucose polymer which have “Up to 1000 glucose unit; no branching”

Specific objective: To test the glucose concentration of the different urine samples

relying to the given table of glucose concentration. Reaction of the Benedict’s

reagent to a reducing sugar.

* Color of reagent: Blue

Samples Observations

Fasting Sample Yellow Solution with WHITE ppt. (++)

Random Sample Green Solution with WHITE ppt. (+)

a. Fasting Sample

- The concentration of this urine ranges to 1.0% or 1000 mg/dL which has

more amount of Amylase Activity.

- This fasting urine is the most suitable because it is the most natural urine that

we excrete and it is not yet mix with the chemicals etc. that we ingest.

b. Random Sample

- The concentration of this urine ranges to 0.5% or 150 mg/dL which has some

amount of Amylase Activity.

- This is not that accurate because at this moment that this urine is tested we

ingested already many kinds of food whether it is a rich in glucose content or

a solvent (water).

SPECIFIC TESTS:

BARFOED’S TEST

A specific chemical test used for detecting the presence of monosaccharides.

. It is based on the reduction of copper(II) acetate to copper(I) oxide (Cu2O),

which forms a brick-red precipitate

The function of the reagent is just like in the Benedict’s test that oxidize the

reducing sugar especially monosaccharide

Barfoed’s test uses copper(II) ions in a slightly acidic medium. (an acid

media) which delays the reaction of disaccharide.

. Reducing monosaccharides forms the copper(I) oxide within 2-3 minutes.

. Reducing disaccharides cause the formation of copper(I) oxide after

approximately 10 minutes.

Here’s the equation that would be observe in this reaction:

Would be responsible for the brick red ppt.

The aldehyde group of the monosaccharide which normally forms a

cyclic hemiacetal is oxidized to the carboxylate

It was invented by Danish chemist Christen Thomsen Barfoed [1]  and is

primarily used in botany.

Specific objective: To detect the presence of reducing sugars through a visible positive

result of formation of brick red precipitate from each samples.

* Color of reagent: Blue

Samples Observations

Glucose Brick red precipitate in blue solution

Sucrose Blue solution

Lactose Blue solution

Glucose: We all know that glucose is a monosaccharide and in this specific test.

Barfoed’s test reacts faster in monosaccharide.

Study Question

d.) Differentiate between the 3 kinds of normal urine samples: fasting, post-prandial

and random. Which sample is the most suitable for use? Explain your answer.

Fasting sample– 12hour urine without any food/drink ingestion.

Random – just simple urine. Without any done actions.

Post-prandial - The patient is given glucose water in a much diluted quantity and

a blood test is conducted after two to two and a half hours.

The fasting urine is the most suitable because it is the most natural urine that we

excrete and it is not yet mix with the chemicals etc. that we ingest.

e.) What is Diabetes Mellitus? Differentiate between Type 1 and Type 2 diabetes. Is it

possible to have sugar diabetes even if no member in the family has it? Explain.

Diabetes mellitus is a kind of metabolic disease that is brought about by either the

insufficient production of insulin or the inability of the body to respond to the insulin

formed within the system.

What is diabetes mellitus type 1?

Diabetes mellitus type 1 is caused by the loss of beta cells found in the islets of

Langerhans in the pancreas.

Beta cells primarily produce insulin and hence, their loss will lead to huge insulin

deficiencies in the body.

In most cases, the loss of the beta cells is caused by an autoimmune attack mediated

by the body’s own T-cells.

Type 1 diabetes mellitus makes up 10% of all the diabetes mellitus cases in Europe

and in North America.

Up until today, there have been no preventive measures found for disease. Most of

the patients who acquire this type of diabetes are found in the younger populations.

Because of this, Type 1 diabetes mellitus is also now known as the juvenile diabetes.

What is diabetes mellitus type 2?

Another type of diabetes mellitus is the type 2 diabetes. Type 2 diabetes is generally

characterized by the body’s resistance to insulin. This is primarily attributed to the loss

of certain insulin receptors in the tissues that are supposed to mediate the entrance of

insulin into the body’s cells.

This particular kind of diabetes is the most common kind that afflicts most of the

reported cases of the disease. Type 2 diabetes usually leads to hyperglycemia which

can be treated by a series of medications that can either improve the body’s insulin

sensitivity or improve the liver’s production of insulin in the system.

The last major category of diabetes mellitus is the gestational diabetes. This type of

diabetes commonly occurs in pregnant women and may disappear or even progress

right after delivery. Gestational diabetes generally manifests the same kind of

complication found in type 2 diabetes.

Just like in type 2 diabetes, the body also exhibits a resistance to insulin and can

sometimes produce insufficient amounts of the substance as well. This kind of

diabetes is fully treatable but may require very close monitoring.

And it is still possible to have a sugar diabetes even is not inherited. DM is also

acquired when we’re engaging in a poor lifestyle and abandoned our self in eating too

much sweets.

f.) Is one considered a diabetic if one obtains a positive result for sugar in a fasting

urine sample? Explain.

No.. Because only the amylase activity is the one that is tested on the urine sample.

The test is not that accurate. Maybe the test only reacts with the reducing sugar. And

nit with the other sugar.