This particular experiment explores the infrared spectroscopy technique used to

Question

This particular experiment explores the infrared spectroscopy technique used to isolate benzoic acid and caffeine in soda and lemonade. The following methodology was followed:

For the cola sample, the mass of caffeine was found to be 0.112 g and the mass of benzoic acid was found to be 0.07 g. On the other hand, for the lemonade sample, the mass of caffeine was found to be 0.11 g and the mass of benzoic acid was found to be 0.06 g.

1. Calculate the concentrations of benzoic acid and caffeine in both samples (cola and lemonade) in grams per liter (g/L). Show full working and comment on the relative amounts of benzoic acid and caffeine present in the lemonade and cola samples.

2. Suggest why benzoic acid is more water soluble in basic solution, while caffeine is more water soluble in acidic solution.

3. Can you tell from this experimental method whether the Food Additive 210 was originally present as sodium, potassium benzoate or benzoic acid? Give a detailed explanation.

Collect samples (150 mL) of soft drinks (you need one sample of lemonade and one of cola) in 500 mL conical flasks. Record the brand name (if provided). A. Isolation of caffeine: (i) Add 2 g of Na2COs to each sample and dissolve. This makes the solution basic test a drop of the solution with pH paper (not litmus paper) it should be about 8 or 9; add more NazCOs if necessary.

Explanation / Answer

1) We have 150 mL of both cola and lemonade. Tabulate the amounts of benzoic acid and caffeine in cola and lemonade as below.

Caffeine

Benzoic Acid

Mass in grams in cola

0.112

0.07

Mass in grams in lemonade

0.110

0.06

Volume of cola/lemonade in mL

150

150

Volume in L

(150 mL)*(1 L/1000 mL) = 0.15 L

(150 mL)*(1 L/1000 mL) = 0.15 L

Concentration in cola in g/L

(0.112/0.15) = 0.747 ? 0.75

(0.07/0.15) = 0.467 ? 0.47

Concentration in lemonade in g/L

(0.110/0.15) =

(0.06/0.15) = 0.400

2) Benzoic acid contains the acidic carboxylic (-COOH) group. The acid group participates in acid-base reaction with a base (say NaOH) to form an ionic salt (carboxylate salt, contains the -COO- ion). Since an ionic salt is formed, the solubility of benzoic acid increases in aqueous solution when a base is added, i.e, benzoic acid is soluble in aqueous base.

Caffeine contains an imidazole group (cyclic ring containing C=C and C=N moieties). The imdidazole N atom is basic in nature and picks up a proton from a mineral acid (like HCl). Hence, caffeine is soluble in an aqueous acid.

Caffeine

Benzoic Acid

Mass in grams in cola

0.112

0.07

Mass in grams in lemonade

0.110

0.06

Volume of cola/lemonade in mL

150

150

Volume in L

(150 mL)*(1 L/1000 mL) = 0.15 L

(150 mL)*(1 L/1000 mL) = 0.15 L

Concentration in cola in g/L

(0.112/0.15) = 0.747 ? 0.75

(0.07/0.15) = 0.467 ? 0.47

Concentration in lemonade in g/L

(0.110/0.15) =

(0.06/0.15) = 0.400

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