Lactic acid C3H6O3 is found in sour milk where it is produced by the action of lactobacilli in lactose or the sugar in milk. The pH of a 0.045 M solution of lactic acid was determined using a pH probe and found to be 2.63. a. Calculate the equilibrium constant for this acid. b. Had you not been given the pH of the acid and you had to measure it yourself, how would the method in part 2 be applied to the determination of Ka? Would you expect an improvement in the accuracy of your result with the application of the method of this experiment? Explain why or why not.

see explanation below

Explanation:

In this case, we need to write the overall reaction:

HC₃H₅O₃ + H₂O <> C₃H₅O₃⁻ + H₃O⁺

The lactic acid is a weak acid, so, when it dissociates in it's ions, part of the acid is dissociated. This depends of it's Ka to know which quantity was dissociated.

To calculate Ka, let's write an ICE chart first:

     HC₃H₅O₃ + H₂O <> C₃H₅O₃⁻ + H₃O⁺      Ka = ?

i)       0.045                                  0            0

c)          -y                                     +y           +y

e)   0.045 - y                                 y              y

Writting the Ka expression we have:

Ka = [C₃H₅O₃⁻] [H₃O⁺] / [HC₃H₅O₃]

Now, to calculate Ka we need the values of [C₃H₅O₃⁻] and [H₃O⁺] in equilibrium. Fortunately, we have the value of the pH, which is 2.63 and with this we can get the value of [H₃O⁺] and then, the value of y. With that value, we replace it in the Ka expression to calculate Ka:

[H₃O⁺] = 10^(-pH)

[H₃O⁺] = 10^(-2.63)

[H₃O⁺] = [C₃H₅O₃⁻] = x = 2.34x10⁻³ M

Now, let's replace this value in the Ka expression:

Ka = (2.34x10⁻³)² / (0.045 - 2.34x10⁻³)

Ka = 1.28x10⁻⁴

b) Now, let's calculate the pH with the obtained value of Ka. We will use the same expression of Ka so:

1.28x10⁻⁴ = y² / (0.045-y)    

1.28x10⁻⁴ (0.045 - y) = y²

5.76x10⁻⁶ - 1.28*10⁻⁴y = y²

y² + 1.28x10⁻⁴y - 5.76x10⁻⁶ = 0

From here, we'll use the quadratic equation general formula, for solving y:

y = -1.28x10⁻⁴ ±√(1.28x10⁻⁴)² + 4 * 1 * 5.76x10⁻⁶ / 2

y =  -1.28x10⁻⁴ ±√2.31x10⁻⁵ / 2

y = -1.28x10⁻⁴ ± 4.8x10⁻³ / 2

y₁ = 2.34x10⁻³ M

y₂ = -2.464x10⁻³ M

Now, as y₁ is positive this is the value that we will take.

This value would be the [H₃O⁺] in equilibrium.

The value of pH would be:

pH = -log[H₃O⁺]

pH = -log(2.34x10⁻³)

pH = 2.631

According to this value of pH we can actually expect an inprovement in the accuracy, basically because we obtain a value with more significant figures, and this are relationed with accuracy.

quartz

explanation:

according to the u.s. department of agriculture, the label of "certified organic" comes with a set of highly regulated standards for environmental stewardship and resource conservation. some of these include maintenance and improvement of soil quality, prevention of ground and surface water contamination, greenhouse gas regulation, encouragement of biodiversity and conservation of water and energy (see references 1). organic practices integrate natural methods such as mulching, plant diversity, native and adapted plants, crop rotation and the introduction of beneficial insects to control pests without synthetic pesticides.

environmental implications of pesticides

synthetic pesticides ensure high crop yields. while effective in achieving this goal, pesticides contaminate soil, air, ground and surface water, as well as the plants and animals that come into contact with these contaminated sources. freshwater and marine organisms are particularly susceptible to pesticides through agricultural runoff. pesticides also reduce soil fertility (necessitating the use of synthetic fertilizers) and can travel far from the original source, contaminating water and air hundreds of miles from the location of application (see references 2).

health implications of organics

although a subject of particular debate, many recent findings show that organic food is healthier than conventionally grown food. according to the usda, an extensive european union-funded study found that organically grown foods contain more beneficial compounds, such as the vitamins and antioxidants needed to combat many diseases (see references 5). organic milk, meat and eggs are regulated to ensure they are free of hormones administered to conventional livestock and poultry.

health implications of pesticides

pesticides affect human health in three ways: through skin contact, inhalation and ingestion. acute and long-term exposure to pesticides can cause serious health problems for farmers who apply them. the majority of other people are affected by drinking contaminated water and eating contaminated marine life (see references 3). pesticides have been linked to neurological disorders, endocrine and reproductive disorders, immune system deficiencies and cancer. according to the world health organization, acute pesticide poisoning (app) is responsible for significant annual mortality, especially in developing nations (see references 4).

other important considerations

not every small farm or business owner can afford the costly certification process required to be considered "certified organic," even if the farm is not using chemicals. "transitional" farms include those that once used chemicals and are now transitioning to organic-only production. in addition, though organic farming methods offer obvious environmental benefit, an organic apple shipped from around the world creates a different set of environmental problems. locally grown food (particularly locally grown, organic food) is key in sustainable food production.