experiment 15. reactions of carboxylic acids
TRANSCRIPT
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Experiment 15Reactions of Carboxylic Acids
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Pre-laboratory Questions:
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DRAW THE STRUCTURAL FORMULA OF THE FOLLOWING COMPOUNDS:
Acetic acid, monochloroacetic acid, trichloroacetic acid, benzoic acid, oxalic acid, succinic acid, lactic acid, tartaric acid, citric acid and propionic acid.
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Acetic acid
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Monochloroacetic acid
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Trichloroacetic acid
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Benzoic acid
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Oxalic acid
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Succinic acid
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Lactic acid
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Tartaric acid
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Citric acid
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Propionic acid
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WRITE THE EQUATION THAT SHOWS THE IONIZATION OF VALERIC ACID IN WATER.
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+ H2O H3O +
+
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WRITE EQUATIONS SHOWING THE REACTIONS OF VALERIC ACID WITH NAOH AND NAHCO3.
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+ NaOH
+ NaHCO3 + CO2 + H2O
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RESULTS & DISCUSSIONS
A. ACIDITY AND STRUCTURE
Acetic acid Monochloroacetic acid
Trichloroacetic acid
pH 3.0 2.0 1.0
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Trichloroacetic acid is more acidic because of the presence of the 3 chlorine atoms which tend to pull the electrons closer leaving the
Hydrogen more prone to leave
DISCUSSION:
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B. SOLUBILITY
Water NaHCO3
Acetic Acid - 0.5 mL
Benzoic Acid Did not dissolve 0.5 mL
Oxalic Acid 0.5 mL 0.5 mL
Lactic Acid 0.5 mL 1 mL
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EFFECT OF OXIDIZING AGENTSKMnO4 Tollens’ Reagent
Formic acid Purple to green (w/o heating)Green to brown (after heating)
Silver mirror formed
Acetic acid No change in color No silver mirror formed
Lactic acid Purple to green (w/o heating)Green to brown (after heating)
No silver mirror formed
Tartaric acid Purple to bloody red (w/o heating)Bloody red to clear sol’n (after
heating)
No silver mirror formed
Citric acid Purple to clear sol’n No silver mirror formed
Oxalic acid No change in color No silver mirror formed
Benzoic acid No change in color No silver mirror formed
Propionic acid Purple to reddish brown (after heating)
White precipitate
Water No change in color No silver mirror formed
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FORMIC PROPIONIC TARTARIC CITRIC ACETIC
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OXALIC LACTIC BENZOIC
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DISCUSSION for KMnO4
•Carboxylic acids are relatively resistant to oxidation. However, some acids, like alpha-hydroxy acids may be oxidized.
Acetic acid Lactic acid
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DISCUSSION for Tollen’s Reagent
• Mild oxidizing agents like Tollen’s reagent are easily reduced by aldehydes to silver mirror.
O
CH OH
Formic acid
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ESTERIFICATION
• Smells like Guava ; • Did not dissolve in water
DISCUSSION:
There are two evidences of esterification reactions:
1. The change in solubility – the product ester is not water soluble, so two layers were formed
2. A distinctive change in odor – they are usually sharp and extremely pleasant
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CARBOXYLIC ACID AND ITS SALTS
Cold water: salicylic acid did not dissolve
Hot water: salicylic acid dissolved
When cooled to room temperature: crystals were formed
Addition of 3M NaOH in erlenmeyer flask: crystals were dissolved
Addition of 3M HCl in erlenmeyer flask: crystals were reformed
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QUESTIONS
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1. What is the effect of Cl on the acidity of carboxylic acids?
Cl is electronegative which tends to pulls electrons closer to them leaving the hydrogen more readily to leave making it highly acidic
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2. Explain the effect of the structure of the
samples used on solubility behavior.
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Acetic acid
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Monochloroacetic acid
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Trichloroacetic acid
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Benzoic acid
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Oxalic acid
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Succinic acid
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Lactic acid
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Tartaric acid
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Citric acid
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Propionic acid
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3. Write the equation showing the ester
formation.
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Conclusion
• In conclusion, the structure of the compounds plays an important role in its solubility.
• Electronegativity plays a big role on the carboxylic acid’s acidity.
• Carboxylic acids are usually resistant to oxidization but there are some cases that they can be oxidized.