Carboxylic acids are organic acids characterized by the presence of a carboxyl group, -COOH. This acid acts as a weak acid, which can react with a strong base. Carboxylic acids form hydrogen bonds with many water molecules and are more soluble with one to four carbon atoms. Also, it may have an R group that consist of hydrogen or an alkyl group that changes its water solubility. Carboxylic acids with low molecular weight have odor at room temperature and higher molecular weight are solid and have low vapor pressure which have less molecules that allow us to smell it (Staudt 80).
When H in the carboxyl group is replaced with an alkyl group, it becomes an ester group. “The reaction typically gives 60-70% of the maximum yield” (Staudt, 80). The reaction of an ester could also be reversible to make carboxylic acid and alcohol; this process is called hydrolysis. But when, “the base-promoted decomposition of esters yield an alcohol and a salt of the carboxylic acids; this process is called saponification”; In other words, it is the process of making soap (Staudt 80). Moreover, Esters are liquid at room temperature no matter how low or high their molecular weight is; therefore, they have high vapor pressure and provide stronger odor that is distinguishable (Staudt 80).
It is easy to distinguished between carboxylic acids and esters through their distinctive odors. Carboxylic acids usually have a sour odor that is not distinguishable with any specific scent. Meanwhile, “esters have sweet and pleasant odors often associated with fruits” (Staudt 80).
In this lab, solubility in water, acidity, and odors of carboxylic acids will be observed. Also, esters will be produce and odors will be detected from the product. Finally, saponification will be learned.
Carboxylic Acids and Their Salts: Characteristics of acetic acid:
2mL of water and 10 drops of glacial acetic acid was placed into a clean, dry test tube. Before continuing on to the next step, the smell was noted by waving the hand slightly above the open end of the test tube. Next, wetting the glass rod of the solution and dipping it onto the indicator paper determined pH of the solution. After that, 2mL of 2M NaOH was added to the previous mixed solution to prepare a basic solution and its pH was tested to determine if it is basic or not. Again, the smell was noted after it was basic. Once it was basic, dropwise addition of 3M HCl was added to the solution until it became an acid again, pH was tested to determine it acidity, and the smell was noted.
Carboxylic Acids and Their Salts: Characteristics of benzoic acid:
0.103g of benzoic acid along with 2mL of water were added to a clean, dry test tube. Then, tapping the test tube with my finger mixed it and smell was noted. Then, 1mL of 2M NaOH was added to the solution and mixed by tapping. The odor was examined and what happened to the solid benzoic acid. Afterwards, 3M HCl was added dropwise to acidify the solution and pH was tested with pH paper to determine its acidity. The solution was observed when it returned acidic.
Table 1 Acids and Alcohols
Test Tube No.| Carboxylic Acid| Alcohol|
1| Formic | Isobutyl|
2| Acetic| Benzyl|
3| Acetic| Isopentyl|
4| Acetic| Ethyl|
5| Salicylic| Methyl|
10 drops of liquid carboxylic acid and 10 drops of alcohol according to the order of Table 1 were carried out. The odor was noted from each test tube. Then 5 drops of sulfuric acid was added to each test tube and mixed thoroughly. All of the test tubes were placed in a water bath with the temperature of 6O degree Celsius for 15 minutes. After the time was up, all of the test tubes were placed in an ice bath until cool and 2mL of water was added. Then a Pasteur piper was used to transfer some of the layer from the solution onto a watch glass to note the odor.
10 drops of methyl salicylate and 5...