What chemical properties does sugar have?

To start with we should an­swer the sec­ond ques­tion. The fact is that sug­ars (car­bo­hy­drates) are an enor­mous class of the most var­ied com­pounds, which in their turn are di­vid­ed into sev­er­al class­es.

Monosac­cha­rides are com­pounds which con­sist of one mol­e­cule. They are monomers. They in­clude glu­cose, fruc­tose, galac­tose, mal­tose, and all kinds of less com­mon com­pounds that con­sist of a greater or small­er num­ber of car­bon atoms (for ex­am­ple, pen­toses, that are part of the nu­cleo­tides of DNA).

Dis­ac­cha­rides are com­pounds which con­sist of two monomer mol­e­cules. For ex­am­ple, su­crose.

Poly­mers con­sist of mil­lions of monomers. For ex­am­ple, starch and cel­lu­lose.

This clas­si­fi­ca­tion is im­por­tant be­cause each sub-group of these com­pounds is char­ac­ter­ized by cer­tain qual­i­ties which are not found in oth­er sub-groups of sug­ars. So we should ex­am­ine sug­ars (their chem­i­cal fea­tures) based on this clas­si­fi­ca­tion, and it is not quite cor­rect to dis­cuss the chem­i­cal prop­er­ties of sug­ar, as glu­cose, for ex­am­ple, may dis­play quite dif­fer­ent prop­er­ties from su­crose or starch.

Chem­i­cal qual­i­ties of monomer car­bo­hy­drates.

We will ex­am­ine them based on the ex­am­ple of glu­cose – the sug­ars present in the me­tab­o­lism of hu­man be­ings, an­i­mals and plants are of the great­est im­por­tance. Ad­di­tion­al­ly, this com­pound is wide­ly used in medicine and in­dus­try.

1. Al­co­hol fer­men­ta­tion is the re­ac­tion that prob­a­bly has the widest prac­ti­cal use. Yeast mi­cro-or­gan­isms cause glu­cose mol­e­cules to trans­form into ethyl al­co­hol. Ad­di­tion­al­ly, if lac­tic or bu­tyric bac­te­ria re­act with glu­cose, lac­tic or bu­tyric acids will be formed.
2. There is a qual­i­ta­tive re­ac­tion known as the sil­ver mir­ror. As the alde­hyde group is present in glu­cose, when it re­acts with an am­mo­nia so­lu­tion of sil­ver ox­ide, a sil­ver residue will form (this will in fact be pure sil­ver).
3. The re­ac­tion of glu­cose with cop­per hy­drox­ide is char­ac­ter­is­tic – the so­lu­tion will change col­or from blue to red (the rea­son is that cuprous cop­per ox­ide forms). It is im­por­tant to note that this re­ac­tion is only pos­si­ble when the sub­stances are heat­ed – at room tem­per­a­ture the al­co­hol groups will cause the so­lu­tion to turn dark blue (sim­i­lar to the qual­i­ta­tive re­ac­tion with glyc­erin, a polyal­co­hol).
4. An­oth­er re­ac­tion with prac­ti­cal sig­nif­i­cance is the hy­dro­gena­tion of glu­cose to sor­bitol, a hex­ahy­dric al­co­hol (again, this is pos­si­ble be­cause of the pres­ence of the alde­hyde group in the glu­cose mol­e­cule).
5. And of course, we can­not for­get the re­ac­tion of poly­mer­iza­tion, when a huge num­ber of mol­e­cules of glu­cose (or an­oth­er monomer car­bon) join to­geth­er and starch is formed (or cel­lu­olose).

Chem­i­cal qual­i­ties of dis­ac­cha­rides

As it is wide­ly be­lieved by the gen­er­al pub­lic that sug­ar is a white, crys­talline sub­stance that is sweet to the taste, we will ex­am­ine the prop­er­ties of su­crose. Es­sen­tial­ly, no re­ac­tions that dif­fer from glu­cose can be not­ed (as the alde­hyde group is “joined”). The only dif­fer­ence is that un­der the in­flu­ence of wa­ter, this sub­stance will break down into glu­cose and fruc­tose mol­e­cules.

Qual­i­ties of poly­mer­ic car­bo­hy­drates

The re­ac­tion of de­poly­mer­iza­tion is the break­down of starch into glu­cose, and ad­di­tion­al­ly there is a qual­i­ta­tive re­ac­tion of starch and io­dine - it turns blue.

Con­clu­sion

Car­bo­hy­drates (sug­ars) are a very wide group of sub­stances, the qual­i­ties of which are de­ter­mined by the num­ber of “build­ing blocks” in the com­pound. Here you'll find in­ter­est­ing ex­per­i­ments with sug­ar.