Determine the molecular formula for table sugar (sucrose)
Draw a Lewis Structure for sucrose
Classify the molecule fully fex, Primary amine, aliphatic)
From your Lewis Structure and knowledge of linkages, identify the structures (names are NOT Important) of the parent molecules that formed sucrose.
Describe the 3 dimensional shape of the central atoms of sugar using VSEPR. Include the bond angles on your Lewis structure
Show the hybridization filling diagram for the bonds around one of the carbon atoms and one of the oxygen atoms in the molecule
Determine the reaction for the complete combustion of sugar
Assign oxidation numbers to determine if this process is redox make a conclusion and justify it
The Correct Answer and Explanation is :
Molecular Formula for Sucrose (Table Sugar)
Sucrose is composed of carbon (C), hydrogen (H), and oxygen (O). Its molecular formula is:
C₁₂H₂₂O₁₁
This means sucrose contains 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms.
Lewis Structure for Sucrose
The Lewis structure of sucrose is quite complex because it contains multiple atoms and bonds. The molecule consists of two monosaccharides: glucose and fructose, linked by a glycosidic bond. The structure looks like this:
- Two carbon rings (one in glucose and one in fructose), with oxygen atoms between them. The glycosidic bond is between the oxygen atoms of the two sugars.
- Hydroxyl groups (OH) are attached to the carbons in the sugar rings.
Classification of the Molecule
Sucrose is classified as:
- Aliphatic: It is a compound made from carbon atoms that are linked in open chains (with no aromatic rings).
- Not a primary amine: It does not contain a nitrogen atom.
Parent Molecules That Formed Sucrose
Sucrose is formed by the condensation of two monosaccharides:
- Glucose (C₆H₁₂O₆), an aldose sugar.
- Fructose (C₆H₁₂O₆), a ketose sugar.
These two monosaccharides are linked by a 1,2-glycosidic bond between the oxygen of the glucose and fructose molecules.
3D Shape of the Central Atoms Using VSEPR
The central atoms in sucrose are mostly carbon and oxygen. Here’s the VSEPR analysis for some of the central atoms:
- Carbon (C): Most carbons in sucrose are bonded to four other atoms (hydrogens, other carbons, or oxygen), and they will have a tetrahedral shape with bond angles of approximately 109.5°.
- Oxygen (O): The oxygen atoms typically form two bonds (either with carbon or hydrogen) and have a bent shape with bond angles of approximately 104.5° due to the lone pairs.
Hybridization and Bonding
The hybridization of the carbon and oxygen atoms involved in the bonds is as follows:
- Carbon atoms in sucrose are typically sp³ hybridized (tetrahedral geometry), as they form single bonds with other atoms.
- Oxygen atoms are typically sp³ hybridized as well because they form two single bonds with carbon and hydrogen.
Reaction for the Complete Combustion of Sugar
The complete combustion of sucrose (C₁₂H₂₂O₁₁) involves reacting it with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O):
[
C_{12}H_{22}O_{11} + 12 O_2 → 12 CO_2 + 11 H_2O
]
Oxidation Numbers and Redox Reaction
To determine if the combustion of sucrose is a redox reaction, we assign oxidation numbers:
- In sucrose, the carbon atoms generally have oxidation numbers between 0 and +4, oxygen atoms are usually -2, and hydrogen atoms are +1.
- In carbon dioxide (CO₂), the carbon is oxidized to +4, while in water (H₂O), hydrogen is oxidized to +1 and oxygen is reduced to -2.
Since there is a change in oxidation states (carbon going from 0 to +4, oxygen going from -2 to 0), this is a redox reaction.
Conclusion
The combustion of sucrose is a redox reaction, as oxidation and reduction occur. The carbon in sucrose is oxidized to carbon dioxide, and oxygen is reduced from O₂ to H₂O. This illustrates how the combustion of organic compounds typically involves both oxidation and reduction processes.