This subtopic builds upon the concept of repeating units introduced in Stage 1 subtopic 3.4.

Carbohydrates are naturally occurring sugars and their polymers. They are defined as either polyhydroxy aldehydes or polyhydroxy ketones, or substances that form these compounds on hydrolysis.

• Given its structural formula, determine whether a molecule is a carbohydrate.

Definition of carbohydrates

Video

Disaccharides and polysaccharides are produced by the condensation of monosaccharide units linked in chains by covalent bonds.

• Write molecular formulae for glucose, and for disaccharides and polysaccharides, based on glucose monomers.
• Draw the structural formulae of the monosaccharide(s), given the structural formula of a disaccharide.
• Identify the repeating unit and draw the structural formula of the monomer, given the structural formula of a section of a polysaccharide.

Examples of carbohydrates

In aqueous solution there is an equilibrium between a ring form and a chain form of glucose.

• Explain the ability of glucose to react as an aldehyde when in chain form but not when in ring form.

Video: Structure of glucose

Video: Silver mirror test (glucose reacts in this way due the aldehyde form present)