Dolomite, [CaMg(CO3)2] is found in a soil sample. A geochemist titrates 24.65 g of soil with 57.85 mL of 0.3315M HCl. What is the mass % of dolomite in the soil? ( Write answer to two decimal places, ex. 15.77) Following is the acid/base reaction which occurs during the titration: CO3-2(aq) + HCl(aq) --> HCO3-(aq) + Cl-(aq)

A buffer with a pH of 4.06 contains 0.13 M of sodium benzoate and 0.18 M of benzoic acid. What is the concentration of [H ] in the solution after the addition of 0.052 mol of HCl to a final volume of 1.3 L? Assume that any contribution of HCl to the volume is negligible.

mass of empty beaker-----------132.862 g

mass of beaker with unknown sample--------133.343g

ass of crucible------------41.962g

mass of crucible with BaSO4---------------42.631g

A) calculate the number of moles of BaSO4 that were collected

B) calulate the number of moles of SO4^2- ion that were in the unknown

C) calulate the mass of the sulfate ion in the unknown

D) calculate the mass percentage of the sulfate ion in the unknown sample.

In the laboratory, a general chemistry student measured the pH of a 0.550 M aqueous solution of formic acid, HCOOH to be 1.987.

Use the information she obtained to determine the K_a for this acid.

K_a(experiment) =

4. An ideal gas in a moveable piston is allowed to reversibly expand by slowly heating at constant pressure.

a. (10 pts) Derive the equation for the work done (w reversible) as a function of the initial and final temperatures.

b. (10 pts) Derive the equation for the change in heat in the system (q).

c. (10 pts) Derive the equation for the change in entropy.

2. A 1.00L piston with 1.00mole of an ideal gas at 298.0K and 1.00bar is isothermally and reversibly compressed to a final volume of 0.100L, then irreversibly expanded in 1 step to its original volume with an applied pressure of 1.00bar.

a. (6 pts) Calculate the change in heat for the system (q sys) for the compression and expansion steps.

b. (6 pts) Calculate the change in entropy for the compression and expansion steps.

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c. (6 pts) Calculate the net change in entropy for the compression and expansion steps together.

d. (6 pts) Is there a net change in entropy for the system? If so, why; if not, why not?

e. (6 pts) Is there a net change in the entropy for the surrounding? If so, why; if not, why not?

Sketch a graph for a titration of a weak acid (burette) against 25cm^3 of a strong base (conical flask). Assume that both have concentrations of 0.5M. Label Axes.

What is the pH of a 2:1 mixture of H2PO4– to HPO42– at 0.050 M ionic strength? (See the table for the activity coefficients.)

What is the percent dissociation of a 0.0217 M solution of chloroacetic acid, (HC2H2ClO2 )? (Ka = 1.35 × 10−3 )

What is the concentration of ammonia in a solution if 20.90ml of a 0.1110 M solution of HCl are needed to titrate a 100.0ml sample of a solution?

A materials scientist has created an alloy containing aluminum, copper, and zinc, and wants to determine the percent composition of the alloy. The scientist takes a 11.470 g sample of the alloy and reacts it with concentrated HCl. The reaction converts all of the aluminum and zinc in the alloy to aluminum chloride and zinc chloride in addition to producing hydrogen gas. The copper does not react with the HCl. Upon completion of the reaction, a total of 9.77 L of hydrogen gas was collected at a pressure of 724 torr and a temperature of 27.0 °C. Additionally, 2.169 g of unreacted copper is recovered. Calculate the mass of hydrogen gas formed from the reaction.

- Calculate the mass of aluminum in the alloy sample

- what is the mass percent composition of the alloy (percentage of the Cu, Al and Zn)

A materials scientist has created an alloy containing aluminum, copper, and zinc, and wants to determine the percent composition of the alloy. The scientist takes a 11.470 g sample of the alloy and reacts it with concentrated HCl. The reaction converts all of the aluminum and zinc in the alloy to aluminum chloride and zinc chloride in addition to producing hydrogen gas. The copper does not react with the HCl. Upon completion of the reaction, a total of 9.77 L of hydrogen gas was collected at a pressure of 724 torr and a temperature of 27.0 °C. Additionally, 2.169 g of unreacted copper is recovered. Calculate the mass of hydrogen gas formed from the reaction.

- Calculate the mass of aluminum in the alloy sample

- what is the mass percent composition of the alloy (percentage of the Cu, Al and Zn)

Calculate the concentrations of all species present (H2CO3, HCO−3, CO2−3, H3O+ and OH−) in 0.017 M H2CO3. I already found the pH to be 4.07. H2CO3 (Ka1=4.3×10−7; Ka2=5.6×10−11).

Determine the theoretical oxygen demand for the following solutions:

(a) 200 mg/L of acetic acid, CH₃COOH

(b) 40 mg/L of ethanol. C₂H₅OH

(c) 64 mg/L of sucrose, C₂H₁₂O₆.

All reactions are of the form: CH₃COOH + O₂ >> CO₂ + H₂O

You are given 1 liter of each of the following solutions: 1M HCl, 1M NaOH, 1M NH₃ , 1M HC₂H₃O₂ , 1MNH₄Cl, 1MNaC₂H₃O₂

a) Describe 4 different methods for preparing a buffer solution

b) Describe how you would prepare 400 ml a buffer with a pH= 4.74 and a buffer with pH= 9.25

c) Draw titration curves for : strong acid-strong base, strong acid-weak base, strong base-weak acid. Label the graph axes, indicate initial pH and pH at equivalence.