Q.On adding conc. $H_2SO_4$ to sugar a black mass is obtained. Identify the black mass.

Chitin is built from repeating N-acetyl-D-glucosamine monomers joined by beta-1,4 glycosidic linkages.

Chitin is a structural homopolysaccharide, chemically very similar in architecture to cellulose (which is a beta-1,4-linked chain of plain D-glucose units), but chitin's repeating monomer is instead N-acetyl-D-glucosamine — a glucose derivative in which the hydroxyl group at carbon-2 is replaced by an acetylated amino group (-NHCOCH3). This substitution allows chitin to form very strong hydrogen-bonded microfibrils, which is why it makes such a tough structural material (fungal cell walls, insect and crustacean exoskeletons). The other options are the monomers/hydrolytic components of different molecul …

Cellulose is a homopolysaccharide of β-D-glucose units, and the glucose monomers are linked together specifically by β-(1→4) glycosidic bonds, giving it a straight, unbranched, highly hydrogen-bonded chain.

Cellulose is the chief structural polysaccharide of plant cell walls. It is built entirely of D-glucose units in the β-anomeric configuration, joined by glycosidic bonds between carbon-1 of one glucose unit and carbon-4 of the next — hence a β-(1→4) linkage.

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Lactose = galactose + glucose joined by a $\beta$-1,4-glycosidic bond.

Lactose is a disaccharide made of one unit of $\beta$-D-galactose and one unit of $\beta$-D-glucose. The two monosaccharides are joined through their C-1 (of galactose, $\beta$-configuration) and C-4 (of glucose) carbons, i.e. a $\beta$-1,4-g …

Maltose is two $\alpha$-D-glucose units joined between C1 of one and C4 of the other.

Maltose is a disaccharide made of two $\alpha$-D-glucopyranose units linked through an $\alpha$-1,4-glycosidic bond — the anomeric (C1, $\alpha$-configured) carbon of one glucose unit is joined via an oxygen bridge to the C …

Concentrated sulphuric acid removes the elements of water from sucrose, charring it to carbon.

Concentrated sulphuric acid is a powerful dehydrating agent. On sugar (sucrose, $C_{12}H_{22}O_{11}$), it removes water (in the ratio corresponding to the empirical formula, effectively $H_2O$ units) from the sugar molecule, leaving behind a black, porous mass of elemental carbon and releasing heat and steam/gases …

Ribose's open-chain form has OH on C2/C3/C4 (secondary) and C5 (primary).

The open-chain structure of ribose (an aldopentose) is $CHO-CHOH-CHOH-CHOH-CH_2OH$ (C1 to C5).

• C1 bears the aldehyde group ($-CHO$), no $-OH$ here.
• C2, C3, C4 each bear a hydroxyl on a carbon attached to two other carbons — these are secondary hydroxyls (3 in total). …