Q3. What is the molar mass of hexanedioic acid, HOOC(CH2)4COOH? (C = 12, H = 1, O = 16.)
Its formula is C6H10O4: 72 + 10 + 64 = 146 g mol−1 (reasoned).
Q4. Palmitic acid has 16 carbon atoms, counting the carboxyl carbon (NCERT Class 11 Biology, Chapter 9, page 106). Write the formula of its sodium soap and find its molar mass. (C = 12, H = 1, O = 16, Na = 23.)
Palmitic acid is C15H31COOH, so the soap is sodium palmitate, C15H31COONa, that is C16H31NaO2: 192 + 31 + 23 + 32 = 278 g mol−1 (reasoned).
Q5. How would you show that vinegar contains a carboxylic acid?
Add sodium hydrogencarbonate: carbon dioxide is given off with effervescence, the reaction NCERT says “is used to detect the presence of carboxyl group in an organic compound” (NCERT page 249), and the answer to give in an exam. Strictly, the fizz shows an acid strong enough to react with a hydrogencarbonate, so it alone does not uniquely identify a carboxyl group (reasoned): 2,4,6-trinitrophenol, which NCERT calls “a strong acid” (Unit 7, page 211), dissolves even in sodium hydrogencarbonate solution (NCERT Laboratory Manual, Unit 8, page 91).
Q6. Benzoic acid is used through two of its derivatives. Name them, give the use of each, and say how each is made from the acid.
Its esters, used in perfumery, are made by treating the acid with an alcohol and a mineral acid catalyst such as concentrated H2SO4 (esterification); sodium benzoate, a food preservative, is the salt it gives with NaOH or NaHCO3 (NCERT pages 249, 251 and 254).