An unknown gas contains 85.63% carbon and 14.37% hydrogen by mass. if 2.00 L of the gas at 298 K and 0.420 atm and weights 1.926 g

A) What is the molar mass of the unknown gas?

B) What is the empirical formula of the gas?

C) What is the molecular formula of the gas?

what is the molarity of a KOH solution if 24.6 ml neutralizes 44.0 mL of a 0.211 M HCI?

In the lab manual you are required to keep a 2 – 3 mm layer of acetone and then add water. A student vaporized the acetone absolutely and state that he can use the residue for the later measurement. What is the biggest defect of doing this comparing to the correct procedure? How the calculated yield and measured boiling range will be affected?

Experiment 4: Extraction of an Antibiotic Introduction The extraction of compounds from plant and animal sources is vital direction used by the pharmaceutical industry in search of new medications. Often the natural products uncovered have undesirable side-effects or lower than desired efficacy. The modification of the structures of natural products can lead to improved pharmokinetics or improved specificity. Extractions are performed by many of us on a daily basis as we brew coffees and teas. Essentially we are using hot water to extract the tasty water soluble esters and flavors from the solids (and some caffeine). Lichens are a symbiotic relationship between a fungus and an algae. The fungi were originally considered be only useful in the absorption of water, to the point they were considered almost parasitic. However, it has become clear that the fungus is responsible for the generation of a very important chemical defense agent, usnic acid. Several lichens native to New England have been shown to have antibiotic properties and usnic acid has been shown to be the agent responsible for this biological activity. Lichens have been used medicinally for thousands of years. There is evidence the Egyptians viewed lichens as medicines. Usnic acid has been found to useful as an antibiotic with activity against several Gram-positive bacteria including skin infections and tuberculosis. There have been reports that usnic acid can cause liver problems.

Experimental Procedure 1. Weigh 4 grams of lichen and place in a 150 ml beaker. 2. Add 50ml of acetone to the 150ml beaker. 3. Stir and crush the lichen in the acetone with a stir-rod or spatula for 30 minutes. 4. Remove the pieces of lichen from the acetone by filtering through a glass funnel with a folded filter paper (15cm) into a 125ml Erlenmeyer flask. 5. Clean the 125ml beaker and transfer the contents of the Erlenmeyer flask. 6. Add two boiling sticks and place the beaker on a hotplate (in the hood) and warm to boiling (setting #4 is usually sufficient). 6. Evaporate almost all the acetone. A layer approximately 2-3mm deep at the bottom of the beaker is all that is required. Some solid may be noted at the meniscus. 22 7. Remove the beaker from the heat and remove the boiling sticks. Return to your bench area. 8. Add 2-4 drops of water until a slightly cloudiness is noted. 9. After the flask has cooled on the bench-top for approximately 3 minutes, filter the small yellow crystals using a Buchner funnel, a vacuum flask (125ml) and an aspirator to apply a vacuum. Use the illustration on page 24 as a guide. 10. Weigh the crystals and calculate a percentage of the lichens that is usnic acid. Note the melting point of the crystals. Results and Calculations. 1. Yield should be noted by weighing the crystals formed and comparing to the initial weight of the lichens. 2. Melting range of the usnic acid should be noted. Waste Management The usnic acid generated in this experiment is not regulated as hazardous waste. Acetone is regulated by the EPA as hazardous wastes because they are ignitable below 140 deg F. 1. The filter paper with ground lichens, from Step 4 of the experiment, is non-hazardous and can be disposed of in the trashcan. 2. The filtrate from step 9 of the experiment contains acetone and is flammable. Dispose of as hazardous waste in the waste container labeled with the respective chemical contents. 4. The usnic acid crystals are non-hazardous so can discarded into normal trash. 5. The vacuum flask used for filtration can be washed with soap and water to remove residue. Any acetone used to rinse should be discarded of as hazardous waste.

In a particular solution, acetic acid is 11% ionized at 25°C. Calculate the pH of the solution and the mass of acetic acid (Ka=1.8x10^-5) dissolved to yield 1.00 L of solution.

pH = __

Mass = __ g

From the standard reduction potentials in Table 11.1 in the Appendix, calculate the standard cell potential and the equilibrium constant at 298.15 K for the following reactions:

(a) 4 NiOOH(s) + 2 H2O(l) ↔ 4 Ni(OH)2(s) + O2(g)

(b) 4 NO3 - (aq) + 4 H+ (aq) ↔ 4 NO(g) + 2 H2O (l) + 3 O2(g)

You are preparing triphenyl carbinol by a grginard synthesis. First you prepare methyl benzoate, and set aside 4.40 grams of the purified ester for later use. You then prepare the grignard reagent ( phenylmagnesium bromide ) by reacting 1.78 grams of magnesium with 12.01 ml of bromobenzene. You add the 4.40 grams of methyl benzoate to the freshly prepared grignard reagent to form an addition product. Finally, after hydrolyzing the grignard addition product, you obtain 5.27 grams of the final product, triphenyl carbinol. What is the percent yield of triphenyl carbinol ? ( The density of bromobenzene is 1.495 g/ml ) (molecular weights: bromobenzene = 157, methyl benzoate=136, magnesium =24.3, triphenyl carbinol =260)

1. The coordination number of a metal atom in a close-packed structure is?

2. The coordination number of a metal atom in a BCC structure is?

3. The coordination number of an atom in the diamond or zinc blende structure is?

4. Metallic hydrogen is a proposed high pressure state of hydrogen with exciting electrical properties. Calculations have been used to propose that this material will have a low coordination number. Of the three cubic structures we have discussed, body centered cubic is the most reasonable.

True or False?

Explain the relationship between light absorbance and solution concentration for a solution which obeys the Beer-Lambert law.

What is the pH of the solution made by mixing 0.2 mol NaH2PO4 and 0.5 mol NaOH with water to make 1.00 L of solution? The pKa values for H3PO4 are 2.12 7.20 and 12.

4) Formic acid (

What is the pH p H change of a 0.200 M M solution of citric acid (pKa=4.77 p K a = 4.77 ) if citrate is added to a concentration of 0.140 M M with no change in volume?

Calculate the enthalpy of oxidation per mole for N₂ and for C₂H₂ (the enthalpy of formation of N₂O₅(g) is 11.30 kJ/mol).

Two proteins with totally different primary structures are capable of binding calcium ions with very high affinity and selectivity. Give an explanation as to why two such proteins, with very different primary structures, would have this capability in common.

(a) Let us consider CH4 combustion in air with an equivalence ratio of 0.9, where we have air flow rate of 400 kg/s. (1) calculate the required flow rate of CH4 (in kg/s), the air-to-fuel ratio on mole basis, and the mole and mass fractions of CO2, H2O, O2, N2 in the product stream. (2) If reactants enter the combustion chamber at 790K, and the products are found to leave the chamber at 1900K, calculate the net heat loss from the combustion chamber. Use constant properties. For all product constituents, use properties near the average temperature of 1345K. (b) Through web search, write down the adiabatic flame temperatures for combustion in air with all reactants at STP, for methane, and hydrogen.