Adapted in part from Wikipedia.
Aqueous Solutions: Acetic Acid in Vinegar
http://www.epicurious.com/expert-advice/how-to-turn-wine-into-vinegar-article
Vinegar has been made and used for thousands of years. Artifacts with traces of it dating from ~3000 BC have been found in Egypt. It has many uses, but now it is mainly used in cooking for pickling, salad dressings, sauces, mustard, ketchup, mayonnaise, chutneys, and marinades. It is often used as a condiment. Its shelf life allows it to last indefinitely without refrigeration, and it is also used in industrial, medicinal, and domestic applications, such as a general household cleaner.
Vinegar is an aqueous solution consisting of about 5-20% acetic acid, CH3COOH, a weak acid and weak electrolyte, which does not ionize completely. It is produced from enzymatic reactions of bacteria with ethanol, which is commonly produced from the fermentation of sugars from a wide variety of natural plant sources. Acetic acid’s taste has historically been regarded as something not very pleasant, although it should more correctly be classified as “sour”, as all acids are generally regarded.
The allegorical Chinese composition above, The Vinegar Tasters, Three Sours, The Vinegar Tasting Old Men, is a traditional theme in ancient Chinese painting. It depicts the three founders of China's major religious / philosophical schools of thought: Confucianism, Buddhism, and Taoism. The three men are dipping their fingers in a vat of vinegar and tasting it; one man reacts with a sour expression, one reacts with a bitter expression, and one reacts with a sweet expression. The three men are Confucius, Buddha, and Lao Tzu, respectively. Confucianism was regarded to view life as sour, in need of rules to correct the degeneration of the people; Buddhism was regarded to view life as bitter, dominated by pain and suffering; and Taoism was regarded to view life’s force as all-encompassing and having an unquestionable goodness when in harmony with nature. Another interpretation of the painting is that, since the three men are gathered around one vat, the "three teachings" are actually embodied in one overarching philosophy.
How Much Acetic Acid Is There in Vinegar?
Experimental Titration Procedure:
https://www.youtube.com/watch?v=9DkB82xLvNE
A standardized sodium hydroxide solution of known concentration will be quantitatively reacted with the acetic acid in vinegar using phenolphthalein as a color indicator to determine the amount of acid in an unknown commercial vinegar sample. This type of experiment is referred to as titration. Titrating the vinegar will provide experimental data to calculate the molarity, and the mass percent of the acetic acid content.
As instructed, pipet a fixed volume of sample into an Erlenmeyer flask, add an approximately equal amount of de-ionized water and 2 drops of phenolphthalein solution. Fill a buret with a standard solution of sodium hydroxide. Add the sodium hydroxide solution slowly to the flask while swirling it until a faint pink color remains and does not disappear with swirling. Record all of your amounts in the table on the reverse side of the handout. Repeat the titration. (Trial #2) Average the volumes of sodium hydroxide used and complete the calculations.
Answer the Post Lab Questions.
Calculating % Acetic Acid in vinegar by titration:
Mass of Acetic Acid (AA) in 10.00 mL of Vinegar from titration [EXAMPLE]
Molar Mass (AA) = MW (AA) in grams/ mole (AA) = 60.056g (AA)/mole (AA)
[Molarity NaOH is provided on the dispensing container.]
In this case, Molarity NaOH = 0.9273 M = 0.9273 mol/L
(Molarity NaOH) x (volume NaOH mL) x (1 L/1000mL) x (1 mole (AA)/1 mole
NaOH) x (60.056 g (AA)/mole AA) = mass (AA)
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Average experimental volume NaOH from titrations: 11.60 mL NaOH
(Molarity NaOH) x (volume NaOH mL) = (Molarity AA) x (volume AA mL)
or
(Molarity NaOH) x (volume NaOH L) = (Molarity AA) x (volume AA L)
(Molarity NaOH) x (volume NaOH mL) / (volume AA mL) = Molarity AA
(0.9273 M NaOH) x (11.60 mL NaOH) / 10.00 mL vinegar sample = 1.076M vinegar
(0.9273 M NaOH) x (11.60 mL NaOH) x (1L/1000mL) = 0.01076
mol NaOH
0.01076 mol NaOH x (1mole AA/1mole NaOH) = 0.01076 mol AA
0.01076 mol AA x (60.056g AA/mole AA) = 0.6462
g (AA)
% of Acetic Acid in Vinegar
[(mass of Acetic Acid)
/ (volume of vinegar) ] * 100% = % Acetic Acid (AA)
[(0.6462 g (AA))
/ (10.00 mL vinegar sample)] * 100 % = 6.462% AA
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Aqueous Solutions: Salt Farming & Lead in Drinking Water
San Francisco Bay & Cuzco, Peru; Flint, Michigan |
Salt's ability to preserve food was a foundation of civilization. It eliminated
the dependence on the seasonal availability of food and it allowed travel
over long distances. It was also a desirable food seasoning. However, salt
was difficult to obtain, and so it was a highly valued trade item. During some ancient periods of time, salt was valued higher than silver and gold. Until
the 1900s, salt was one of the prime movers of national economies and wars.
Salt was taxed from as far back as the 20th century BC in China.
Aside from being a contributing factor in the development of civilization, salt
was also used in the military practice of salting the earth by various peoples,
beginning with the Assyrians.
It is believed that Roman soldiers were at certain times paid with salt,
and this is still evident in the English language as the word "salary" derives
from the Latin word salarium that means payment in salt (Latin sal). The
Roman Republic and Empire controlled the price of salt, increasing it to
raise money for wars, or lowering it to be sure that the poorest citizens
could easily afford this important part of the diet. It was also of high value to the Hebrews, Greeks and other peoples of antiquity. During the late Roman Empire and throughout the Middle Ages salt was a precious
commodity carried along the salt roads into the heartland of the Germanic
tribes. Caravans consisting of as many as forty thousand camels traversed
four hundred miles of the Sahara bearing salt, sometimes trading it for slaves.
It is possible to use solar evaporation of sea water to produce salt. Brine
is evaporated in a linked set of ponds until the solution is sufficiently
concentrated by the final pond that the salt crystalises on the pond's floor.
Salt evaporation ponds are shallow man-made ponds designed to produce salt
from sea water. The seawater is fed into large ponds and water is drawn out
through natural evaporation which allows the salt to be subsequently harvested.
The ponds also provide a productive resting and feeding ground for more than
70 species of waterbirds, including several endangered species. The ponds
are commonly separated by levees.
- Notable salt ponds include the San Francisco Bay salt ponds in the United
States, and the Dead Sea salt ponds in Israel and Jordan. Abandoned
salt pans are a major feature of the southwest coast of Taiwan.
-
San Francisco Bay Salt Ponds:
Due to variable algal concentrations, vivid colors, from pale
green to bright red, are created in the evaporation ponds. The color indicates
the salinity of the ponds. Micro-organisms change their hues as the salinity
of the pond increases. In low to mid-salinity ponds, green algae are predominant.
In middle to high salinity ponds, an algae called Dunaliella salina shifts
the color to red. Millions of tiny brine shrimp create an orange cast in mid-salinity
ponds. Other bacteria such as Stichococcus also contribute tints. These colors
are especially interesting to airplane passengers or astronauts passing above
due to their somewhat artistic formations of shape and color.
Images below: Coffee
colored river high in Peru's Andes with white colored salt covering its
banks; Salt Terraces; 50 kilogram bags of finished salt for market:
worth about US $0.50 per bag.
(To view better quality images click on the image.)
Photos: Diane Goldsmith, SquareMoon Productions
© Copyright 1998 Diane Goldsmith, SquareMoon Productions
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