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A long chain carboxylic acid can be represented by the general formula RCOOH where R represents a hydrocarbon group - VCE - SSCE Chemistry - Question 9 - 2006 - Paper 1
Question 9
A long chain carboxylic acid can be represented by the general formula RCOOH where R represents a hydrocarbon group. In the space below, show the structure of a fat ... show full transcript
Worked Solution & Example Answer:A long chain carboxylic acid can be represented by the general formula RCOOH where R represents a hydrocarbon group - VCE - SSCE Chemistry - Question 9 - 2006 - Paper 1
Step 1
Show the structure of a fat formed by the reaction between glycerol and three molecules of RCOOH.
Answer
To depict the structure of a fat, we start with glycerol, which has the formula C₃H₈O₃. Each molecule of glycerol reacts with three fatty acids (RCOOH) to form a triglyceride. The structure should show the glycerol backbone connected to three ester groups formed from the reaction of glycerol with the carboxylic acids. The ester linkage will be represented as follows:
O O O
|| || ||
C - O - C - O - C
| | |
R1 R2 R3
Where R1, R2, and R3 represent hydrocarbon chains from palmitic acid or oleic acid.
Step 2
Which one of them is classified as an unsaturated carboxylic acid?
Answer
Oleic acid (C₁₈H₃₄O₂) is classified as an unsaturated carboxylic acid because it contains one or more carbon-carbon double bonds in its structure, in contrast to palmitic acid (C₁₆H₃₂O₂), which is saturated and contains no double bonds.
Step 3
Calculate the number of carbon to carbon double bonds present in a molecule of the unsaturated fat.
Answer
-
Molar Mass of H₂: Molar mass of Hydrogen gas = 2 g/mol.
-
Moles of H₂: Given, 15.0 g of H₂:
g/mol, thus:
15.0 g ÷ 2 g/mol = 7.5
- Carbon Double Bonds: Each mole of H₂ reduces one double bond. Therefore, with 2.50 mol of fat, it would require 7.5 moles of H₂: each mole can remove one double bond, which means there were 7.5 double bonds in total. Hence, the number of double bonds present in a molecule of the unsaturated fat is 7.5.
Step 4
Write a balanced equation for the complete combustion (burning) of palmitic acid in the presence of excess oxygen.
Answer
The balanced equation for the combustion of palmitic acid (C₁₆H₃₂O₂) in the presence of excess oxygen is:
C₁₆H₃₂O₂ + 23 O₂ → 16 CO₂ + 16 H₂O
This equation depicts the complete combustion resulting in carbon dioxide and water as the products.
Step 5
Explain how vitamin C acts as an antioxidant.
Answer
Vitamin C, also known as ascorbic acid, acts as an antioxidant by donating electrons to free radicals, thus neutralizing them. This process helps to prevent cellular damage caused by oxidative stress. The ability of vitamin C to stabilize free radicals by donating electrons makes it effective in protecting lipids and other cellular components from oxidation.