CHEM 181 Chapter : woc 12- preserving with sulfites and propionates.docx

Sulfuric acid is the chemical produced in the United States with the highest volume of production. In one of the earliest processes used to make it, an ore containing iron pyrites (FeS2) is roasted (burned) with air. The following reactions take place in the roasting furnace: The gas leaving the reactor goes to a catalytic converter in which most of the SO2 produced is further oxidized to SO3: Finally, the gas leaving the converter passes through an absorption tower, in which the SO3 is absorbed in water to produce sulfuric acid (H2SO4).
(a) An ore containing 82 wt% FeS2 and 18% inerts is fed to a roasting furnace. Dry air is fed to the furnace in 40% excess of the amount theoretically required to oxidize all of the sulfur in the ore to SO3, an FeS2 oxidation of 85% is obtained, with 40% of the FeS2 converted forming sulfur dioxide and the rest forming sulfur trioxide. Two streams leave the roaster: a gas stream containing SO2, SO3, 02, and N2, and a solid stream containing unconverted pyrites, ferric oxide, and inert material in the ore. Calculate the required feed rate of air in standard cubic meters per 100 kg of ore roasted and the molar composition and volume (SCMJ100 kg of ore) of the gas leaving the roasting oven.
(b) The gas leaving the roasting oven enters the catalytic converter, which operates at 1 atm. The conversion reaction [3] proceeds to an equilibrium point at which the component partial the gases are first heated to 600°C, at which Kp = 9.53 atm–1/2, and are then cooled to 400°C, where K,, = 397 atm–1/2. The rate of the forward reaction increases sharply with temperature and is several orders of magnitude greater at 600°C than at 400°C. Calculate the equilibrium fractional conversions of sulfur dioxide in the converter when the temperature is 600°C and when it is 400°C. Briefly explain why the converter gases are initially heated and then cooled.
(c) Assuming complete conversion to sulfuric acid of the sulfur trioxide leaving the converter, how many kg of H2SO4 will be produced per kg of sulfur in the ore? What would this ratio have been if all of the sulfur in the ore had been converted? Summarize the factors responsible for the second number being larger than the firstone.

a) The partial pressure of CO2 in air saturated with water vapor at 25C and 1atm is 3.04E-4 atm. Henry's constant for CO2 is 2.3E-2, and for carbonic acid PKa1=6.37. Assuming that all the dissolved CO2 can be thought of as H2CO3, verify the calculation that the pH of "normal" rainwater is about 5.7.

b) Scientists investigating acid rain measured the pH of a water sample from a lake and found it to be 4.8. The total concentration of dissolved carbonates in the lake is 4.5mmol/L. Determine the molar concentrations of the carbonate species CO3(2-), HCO3(-), and H2CO3 in the lake.

c) Suppose that 1 tonne(1t=10^3kg) of coal that is 2.5% sulfur by mass is burned in a coal-fired plant. What mass of SO2 is produced.

d) What is the pH of rainwater when the SO2 generated part c dissolves in a volume of water equivalent to 2 cm of rainfall over 2.6km^2 (the pKa1 of sulfurous acid is 1.81. Consider the water to be initially pure and at a pH of 7)

e)If the So2 in part c is first oxidized to SO3 before the rainfall, what would the pH of the same rainwater be?

f) one process used to clean SO2 from the emissions of coal-fired plants is to pass the stack gases along with air through a wet calcium carbonate slurry, where the following reaction will take place:

CaCO3s+SO2g+O2g--CaSO4s+CO2g

what mass of limestone (CaCO3) is needed to remove 50kg sulfur dioxide from stack gases if the removal process is 90% efficient?

1.Write the equation that represents the reaction of pyruvic acid in water. (You will find the structure of pyruvic acid in the Common Acids in Biochemistry and Medicinetable. Omit states-of-matter from your answer.)

2.Label the conjugate acid-base pairs. (Omit states-of-matter from your answer. Separate substances in a list with a comma.)
Conjugate acid-base pair that includes pyruvic acid:

3.Conjugate acid-base pair that does not include pyruvic acid: