ChemLab CARBS

What is the general formula of carbohydrates

Cn(H2O)n

What do you call carbohydrates who are polyhydroxy aldehydes

Aldoses

What do you call carbohydrates who are polyhydroxy ketones

Ketoses

Describe the physical properties of mono- & disaccharides compared to polysaccharides

Mono/di - crystalline, water-soluble, sparingly-soluble in organic solvents; Poly - non-crystalline and water-insoluble.

What is a general test

A test designed to identify a chemical group/compound in a certain substance.

What do you call the general test for carbohydrates

Molisch test

What does the Molisch reagent consist of

Alpha-naphthol in 95% ethanol

What does the Molisch reagent specifically identify

Furfural/hydroxymethylfurfural (in the presence of H2SO4).

What indicates a positive test in a Molisch test

Purple color at the interface

Explain how the Molisch test works

Pentoses and hexoses form oxygen-containing rings known as furfural which reacts with the reagent to form colored compounds.

What is the general test for aldehydes

Schiff’s test

What is a positive result for a Schiff’s test

Violet-purple/wine-purple color

What are the constituents of Schiff’s reagent

Para-rosanilin with sulfurous acid

Why do you heat a compound before performing Schiff’s test

To free up an aldehyde group for it to react with the reagent.

What test do you use for reducing sugars resulting in the formation of yellow crystals

Phenylhydrazine test

What does the oxidation of an aldehyde of glucose result to

Gluconic acid

What does the oxidation of an aldehyde of galactose result to

Galactonic acid

What do you call a carbohydrate that reacts with an oxidizing agent to form an aldonic acid

Reducing sugar

Reducing the carbonyl group to a hydroxyl group using what as the reducing agent

Hydrogen

What is the product of the reduction reaction of monosaccharides

Sugar alcohol (ex. D-glucose -> D-glucitol/D-sorbitol)

What is formed when monosaccharides are reacted with methyl alcohol forming acetals and ketals

Glycosides

What is the other name for the Tollen’s test

Silver mirror test

The formation of what is a positive result of the Tollen’s test

Silver mirror formation

Determine the reagent of Tollen’s test

Silver nitrate in ammonia water (or ammoniacal AgNO3)

What is the equation for the oxidation of glucose by Tollen’s reagent

C6H12O6 + [Ag(NH3)2]NO3 -> C6H11O6COOH + Ag + NH4NO3

What tests the reducing property of sugars by using weak oxidizing agent Cu2+ ion

Fehling’s test

What is the positive result for Fehling’s test

Formation of red precipitate

Fehling’s A is made up of

Hydrated CuSO4 solution

Fehling’s B is made up of

Potassium sodium tartrate tetrahydrate/Rochelle salt in NaOH solution (NaOH + KNaC4H4O6 * 4 H2O)

What is formed instead of solid silver in Fehling’s test

Cu2O

Benedict's test has a positive result identified by what

Orange-brown solution, green, yellow-to-orange to brick red ppt. (Formation of green to brick red ppt.)

What is the negative result of Benedict’s test

Blue solution

The reagent of Benedict’s test consists of

Cu2SO4, NaOH, C6H5Na3O7

Nylander’s test has a positive result of what

Formation of black ppt.

What is the reagent of Nylander’s test

Bi(OH)2NO3 (bismuth subnitrate), KOH

What is the positive result of picric acid test

Mahogany red solution

What is the chemical name of picric acid

2,4,6-trinitrophenol (TNP)

Picric acid reacts with metal to form

Metal picrates

What is the positive result of Moore’s test

Formation of dark brown solution (caramel/resinous)

What is the reagent for Moore’s test

Strong NaOH

What is the most abundant of all disaccharides

Sucrose

The bond formed by the reducing ends of both monosaccharides is called what

Glycosidic linkages/bond

Sucrose can exist in one form only in what state

Solid

What enzyme hydrolyzes sucrose to produce invert sugar (glucose and fructose)

Sucrase

What is the specific composition of sucrose

alpha-D-glucose and beta-D-fructose

State the monosaccharide units for maltose, lactose, and sucrose, respectively

Glucose + glucose; glucose + galactose; glucose + fructose