Calculate the enthalpy of the reaction 4B(s)+3O2(g)→2B2O3(s) given the following pertinent information: B2O3(s)+3H2O(g)→3O2(g)+B2H6(g), ΔH∘A=+2035 kJ 2B(s)+3H2(g)→B2H6(g), ΔH∘B=+36 kJ H2(g)+12O2(g)→H2O(l), ΔH∘C=−285 kJ H2O(l)→H2O(g), ΔH∘D=+44 kJ

A 100.0 mL sample of 0.20 M HF is titrated with 0.10 M KOH. Determine the pH of the solution after the addition of 200.0 mL of KOH. The Ka of HF is 3.5 × 10-4.

Answer: 8.14 but how do I get this?? I'm so lost!

Consider the following reaction. It is occuring in a closed system and it is currently at equilibrium:

Label each of the following statements with is effect on the reaction
shift towards products or shift towards reactants or no change: Removing oxygen gas.
shift towards products or shift towards reactants or no change:  Cooling the reaction vessel.
shift towards products or shift towards reactants or no change:  Removing water vapor from the vessel.
  shift towards products or shift towards reactants or no change:  Increase the size of the vessel.
  shift towards products or shift towards reactants or no change:  Decrease the pressure on the reaction vessel

The ethyl mercaptan, C2H5SH, concentration in a mixture was determined by shaking a 1.534-g sample with 60.0 mL of 0.01293 M I2 in a tightly stoppered flask:

2C₂H₅SH + I₂ → 2C₂H₅SSC₂H₅ + 2I^- + 2H⁺

The excess I2 was back-titrated with 10.72 mL of 0.01425 M Na₂S₂O₃:

2S₂O₃^2- + I₂ → S₄O₆^2- + 2I^-

Calculate the percentage of C₂H₅SH (FM = 62.13 g/mol) in the mixture.

(a) 5.67% (b) 3.32% (c) 1.24% (d) 4.33%

(please show work)

An air-purification method for enclosed spaces involves the use of "scrubbers" containing aqueous lithium hydroxide, which reacts with carbon dioxide to produce lithium carbonate and water: 2LiOH(aq) + CO2(g) → Li2CO3(s) + H2O(l) Consider the air supply in a submarine with a total volume of 1.6 × 105 L. The pressure is 0.9970 atm, and the temperature is 25°C. By how much would the pressure in the submarine drop if 2.35 kg of LiOH were completely consumed by reaction with CO2?

atm

A 0.120-L sample of an unknown HNO3 solution required 29.1 mL of 0.200 M Ba(OH)2 for complete neutralization. What was the concentration of the HNO3 solution?

Calculate the ph after mixing 100 ml of .075 M ammonium chloride with 76 ml of .1 M LiOH

Using the particle in the 1-D box model, estimate the first 4 energy levels of the π-network in hexatriene, C6H8 (H2C=CH–CH=CH–CH=CH2). To calculate the box length, assume that the molecule is linear and use the values 135 and 154 pm for the C=C and C–C bonds, respectively. Only 2 out of the 6 ‘π-electrons’ of the 6 C-atoms can occupy each energy level (Pauli exclusion principle). Ignore the rest of the electrons (forming the core and the ??-bonding network). Sketch and label an energy level diagram showing the occupied levels and the first unoccupied one. What is the wavelength of the photon required to induce the HOMO-LUMO transition? Derive the expression for the photon’s wavelength symbolically! How does your numeric result compare with the experimental value of 240 nm?

How many moles of sodium hydroxide would have to be added to 250 mL of a 0.436 M acetic acid solution, in order to prepare a buffer with a pH of 4.630?

moles

Coke can be converted into CO in following reaction CO2(g) + C(s) -> 2CO(g). A coke that contains 84% carbon by mass and the balance noncombustible ash is fed to a reactor with a stoichiometric amount of CO2. The coke is fed at 77 oF, and the CO2 enters at 400 oF. Heat is transferred to the reactor in the amount of 5200 btu/lbm coke fed. The gaseous products and the solid reactor effluent (the ash and unburned carbon) leave the reactor at 1830 oF. The heat capacity of the solid is 0.24 btu/(lbm.oF) Calculate the percentage conversion of the carbon in the coke. (Provide your answer in decimal format, NOT percentage format!)

How many milliliters of 1.27 M KOH should be added to 100. mL of solution containing 10.0 g of histidine hydrochloride (His·HCl, FM 191.62) to get a pH of 9.30?

In an experiment where you standardize EDTA with calcium carbonate and then have EDTA as the titrant and zinc as the analyte to determine the amount of zinc, which of the following are potential sources of error in the determination of the mean and relative standard deviation for the amount of zinc in your unknown?

Select all answers that apply.

1) Lack of homogeneity in the indicator solution

2) Not dissolving calcium carbonate completely

3) Inconsistencies in pipetting the zinc unknown

4) Systematic error in the buret calibrations

5) Failing to quantitatively transfer calcium carbonate

6) Sharing the indicator bottle

7) Over-titrating

Calcium Oxide (CaO) is widely used in the production of cement, steel, medicines and many other familiar materials. It is usually produced by heating and decomposing limestone (CaCO3), a cheap and abundant material, in a calcination process:

CaCO3(s) -> CaO(s) + CO2(g)

CaCO3 at 298 K is fed to a continuous reactor. The calcination is complete, and the products leave at 1000 K. Taking 800 gmol of limestone as a basis and elemental species [Ca(s), C(s), O2(g)] at 298 K as reference for enthalpy calculations.

Ccalculate the required heat transfer to the reactor in MJ.

Malonic acid (H2M) is a diprotic acid. You wish to prepare a buffer of malonic acid (pKa1 = 2.847, pKa2= 5.696) with a final pH of 2.90 but you only have disodium malonate (M2-) in your laboratory shelf. You dissolve 100 mmol of this salt in 1 L of water. Assume both dissociation processes are decoupled.

What is the initial pH of the solution? State any assumptions you make.

How many equivalents of strong acid must you add to your solution to end with only HM- ?

What is the approximate pH of this solution of HM- ? Use an adequate mathematical approximation.

How many additional equivalents must you add to reach the desired pH of 2.90?

Oliver likes to go fishing in the river by his house. One day he noticed that there was a white substance on some rocks at the bottom of the river. When he looked closely, it appeared as though someone had sprinkled a powder or crystals in the water. Moreover, the substance was found mainly where a small creek joined the larger river.

Curious, Oliver followed the creek through the forest toward an industrial area. Eventually, he reached a fence and found the source of the creek water — a large drainage pipe. Oliver noticed that there was steam coming off the water as it flowed out of the metal pipe.

The temperature reading (in ^oC) of the water that flowed out of the drainage pipe: 88.35

The temperature reading (in ^oC) of the water in the river: 7.14

Analysis at four differnt points along the creek and river revealed that the chemical potassium nitrate was found in the water.

1. Explain what is happening, in general terms, by applying your understanding of solutions and solubility.
2. Use the information provided to calculate the concentration of the solution in parts per million (ppm).
   • Point A: 14.7 g of KNO_3(aq) in 1.00 x 10³ L of H₂O_(l)
   • Point B: 1.12 g of KNO_3(aq) in 1.00 x 10² L of H₂O_(l)
   • Point C: 200 mg of KNO_3(aq) in 1.00 x 10² L of H₂O_(l)
   • Point D: 0.061 g of KNO_3(aq) in 1.00 x 10¹ L of H₂O_(l)

   Note that 1 ml of water has a mass of 1 g.

   In addition to potassium nitrate, analysis revealed there was four other chemicals found in the water at Point A.

3. Use the information provided to calculate both the molar mass and molarity for each chemical found in the water.
   • Sodium sulfate: 25.8 g of Na₂SO_4(aq) in 1.00 x 10¹ L of H₂O_(l)
   • Sodium carbonate: 582.2 mg of Na₂CO_3(aq) in 1.00 x 10² L of H₂O_(l)
   • Barium chloride: 6.8 mg of BaCl_2(aq) in 1.00 x 10³ L of H₂O_(l)
   • Magnesium phosphate: 212 g of Mg₃(PO₄)_2(aq) in 1.00 x 10¹ L of H₂O_(l)
   Potassium nitrate: 14.7 g of KNO_3(aq) in 1.00 x 10³ L of H₂O_(l)
4. The pipe used by the factory was made of an alloy of steel (Iron (Fe) = 90%, Carbon (C) = 8.5%, Manganese (Mn) = 1.5%). What amount (in kilograms) of each element was found in the pipe if it has a mass of 24.9 kg?
5. An alloy of gold contains 65% gold (Au), 16.5% silver (Ag), and some copper (Cu). What amount of copper would you expect in 59.8 g of this gold alloy?