A. Carboxylic Acids and Their Salts Materials: Test tubes, glacial acetic acid,
ID: 918629 • Letter: A
Question
A. Carboxylic Acids and Their Salts
Materials: Test tubes, glacial acetic acid, benzoic acid(s), dropper, spatula, pH paper, red and
blue litmus paper, stirring rod, 400-mL beaker, hot plate or Bunsen burner, 10%
NaOH, 10% HCJ
A.1 Write the structural formulas for acetic acid and benzoic acid.
A.2 Place about 2 mL of water in two test tubes. Add 5 drops of acetic acid to one test tube and a small
amount of benzoic solid (enough to cover the tip of a spatula) to the other. Tap the sides of the test
tubes to mix or stir with a stirring rod. Identify the acid that dissolves.
A.3 Test the pH of each carboxylic acid by dipping a stir1ing rod into the solution, then touching it to a
piece of pH paper. Compare the color on the paper with the color chart on the container and report
the pH.
A.4 Place the test tube of benzoic acid (solid should be present) in a hot water bath and heat for 5 minutes.
Describe the effect of heating on the solubility of acid. Allow the test tube to cool. Record
your observations.
A.5 Add about 10 drops of NaOH to each test tube until a drop of the solution turns red litmus paper
blue. Record your observations. Write the equations for the reactions with NaOH including the
structures of the sodium salts formed.
A.6 Add about 10 drops of HCl to each sample until it is neutralized (blue litmus paper turns red).
Record your observations. Write equations for the reactions of the sodium salts that formed.
Write equations for the reactions of the carboxylic acids with NaOH (A.5).
Write equations for the reactions of the salts of the carboxylic acids with HCl (A.6).
A. Carboxylic Acids and Their Salts Acetic Acid Benzoie Acid A.1 Condensed structural formulas A.2 Solubility in cold water A3 pH A.4 Solubility in hot water A.5 NaOH A.6 HCIExplanation / Answer
Completed table below :
acetic acid benzoic acid
A.1 condensed formula CH3COOH C6H5COOH
A.2 solubility in cold water soluble partially soluble
A.3 pH 2.4 (1M) low pH
A.4 solubility in hot water soluble soluble
A.5 NaOH salt formed salt formed ................both are exothermic reactions
A.6 HCl acid(soluble) reprecipitation ................reformation of acids
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after adding HCl acetic acid is formed which remains soluble in water, whereas, benzoic acid formed is insoluble and can be seen as insoluble precipitate in solution.
Chemical equations:
Acetic acid,
with NaOH : CH3COOH(aq) + NaOH(aq) ----> CH3COONa(aq) + H2O(l)
with HCl : CH3COONa(aq) + HCl(aq) ----> CH3COOH(aq) + NaCl(aq)
Benzoic acid,
with NaOH : C6H5COOH(aq) + NaOH(aq) ----> C6H5COONa(aq) + H2O(l)
with HCl : C6H5COONa(aq) + HCl(aq) ----> C6H5COOH(aq) + NaCl(aq)
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