Consider an electrochemical cell involving the overall reaction

2 AgBr(s) + Pb(s) → Pb2+(aq) + 2 Ag(s) + 2 Br–(aq)

Each half-reaction is carried out in a separate compartment. The anion included in the lead half-cell is NO3–. The cation in the silver half-cell is K+. The two half-cells are connected by a KNO3 salt bridge. If [Pb2+] = 1.0 M and [Br-] = 0.14 M, what is the emf of the cell at 298 K?
Given:

AgBr(s) + e– → Ag(s) + Br–(aq)              E° = +0.07 V.

Pb⁺² + 2e– → Pb(s)                                E° = - 0.13 V.

A 16.0 mL sample of a 1.56 M potassium sulfate solution is mixed with 14.3 mL of a 0.890 M barium nitrate solution and this precipitation reaction occurs: K2SO4(aq)+Ba(NO3)2(aq)→BaSO4(s)+2KNO3(aq) The solid BaSO4 is collected, dried, and found to have a mass of 2.51 g . Determine the limiting reactant, the theoretical yield, and the percent yield

If a 0.200 M solution of KOH is added to a solution containing 0.100 M Ni2+, 0.100 M Ce3+, and 0.100 M Cu2+, which metal hydroxide will precipitate first? Calculate the concentration of the first precipitated ion when the second soluble ion begins to precipitate. When the most soluble ion starts to precipitate, what is the concentration for the second soluble ion in the solution?

Ksp Ni(OH)2 = 6.0 X 10-16, Ksp Ce(OH)3 = 6.0 X 10-22, Ksp Cu(OH)2 = 4.8 X 10-20

Heptane and water do not mix, and heptane has a lower density (0.684 g/mL) than water (1.00 g/mL). A 100 mL graduated cylinder with an inside diameter of 3.200 cm contains 39.0 g of heptane and 32.0 g of water. Before we can determine the height of the liquid column, we need to know the total volume of liquid in the cylinder. Which equation expresses the total volume in terms of the volumes of heptane and water?

5) Which of the following statements correctly describe(s) E1 reactions of alkyl halides (RX)?

I.    Rate = k[base]

II. Rate = k[base][RX]

III.       Rate = k[RX]

IV.       The reactions occur in two distinct steps.

V. The reaction involves a carbocation intermediate.

Given the values of ΔH∘rxn , ΔS∘rxn , and T below, determine ΔSuniv .

ΔH∘rxn= 90 kJ , ΔSrxn= 145 J/K , T= 308 K

ΔH∘rxn= 90 kJ , ΔSrxn= 145 J/K , T= 757 K

ΔH∘rxn= 90 kJ , ΔSrxn=− 145 J/K , T= 308 K

ΔH∘rxn=− 90 kJ , ΔSrxn= 145 J/K , T= 403 K

Please show work.

Spontaneous or not?

Approximate the percent increase in waist size that occurs when a 135 lb person gains 35.0 lbs of fat. Assume that the volume of the person can be modeled by a cylinder that is 4.0 feet tall. The average density of a human is about 1.0 g/cm^3 and the density of fat is 0.918 g/cm^3

Express your answer using two significant figures.

50mL of solution in which the analytical concentration of benzoic acid is 0.124 M is titrated with 0.261 M NaOH; if V_e is the volume needed to reach the endpoint, what is the pH at 0 Ve, 1/4 Ve, 1/2 Ve, Ve, and 1.212 Ve?

There are 220 million motored vehicles in the USA, of which about 85% operating on gasoline-fired Otto engines. Gasoline can be assumed 100% octane (C8H18) with a heating value of 48,000 kJ/kg, specific gravity of 0.83, and price of $2.50/gallon. A typical vehicle uses 15% excess air in combustion, and is driven an average of 32 miles per day per vehicle, with an average fuel economy of 18 miles per gallon of gasoline. The averaged unburned Hydrocarbons, CO, and NOx, emissions amount to 0.3%, 0.05%, 0.05% of the exhaust gases respectively.

(a) Balance the combustion equation of C3H18 with 15% excess air, and fine the air-fuel ratio by mass.

(b) Estimate the total combustion air needed, carbon emission, and greenhouse gas CO2 generated from all gasoline engines of USA in Mton/year, and total sale of gasoline in USA in billion$/year.

(c) Estimate total emission of Pollutants: unburned HCs, CO, and NOx from mobile gasoline engines in USA per year.

Explain the following observations: Carbon has two important oxides which are both gases at room temperature. In contrast, silicon dioxide (silica) is a solid with a very high melting point.

Phosphorus pentachloride decomposes according to the chemical equation.

A 0.457 mol sample of PCl5(g) is injected into an empty 4.85 L reaction vessel held at 250

For the diprotic weak acid H2A, Ka1 = 2.6

Calculate the pH for each of the following cases in the titration of 50.0 mL of 0.160 M HClO(aq) with 0.160 M KOH(aq). The ionization constant for HClO is 4.0×10^-8.
(a) before addition of any KOH
pH=
(b) after addition of 25.0 mL of KOH
pH=
(c) after addition of 40.0 mL of KOH
pH=
(d) after addition of 50.0 mL of KOH
pH=
(e) after addition of 60.0 mL of KOH
pH=

One of the main functions of saliva is to buffer against acid from food and plaque, which contributes significantly to the formation of cavities. While there are several buffers in saliva, carbonic acid (H2CO3) has the highest concentration and has the greatest effect on pH.

(a) While the salivary concentration of carbonic acid stays at a fairly constant 1.3 mM, the level of bicarbonate (HCO3-) can vary with the rate that saliva flows from salivary glands. For low flow rates, the bicarbonate concentration is around 2 mM; for medium flow rates, it is 30 mM; and for high flow rates, around 60 mM. The pKa of carbonic acid at body temperature is 6.1. Assuming that the pH of Saliva is determined primarily by carbonic acid and bicarbonate, determine the pH of saliva for each of the three flow rates. The normal pH of saliva is about 6.3.

(b) The most prevalent bacterium in the mouth, streptococcus mutans, breaks down sugar and releases lactic acid (pKa = 3.86). If S. mutans has produced 10^-8 moles of lactic acid since your last swallow, what is the pH of your saliva? What would the pH be without the bicarbonate buffer? Assume that your mouth contains about 1 mL of saliva and that your saliva is flowing at a low rate.

(c) You take a drink of orange juice, and after you swallow, 0.5 mL remains in your mouth. What is the pH of your saliva if your mouth contains 1 mL of pure saliva, and if you model orange juice as 1.0 mM citric acid (pKa = 3.13; assume only one dissociation).

(d) Why do some toothpastes contain baking soda (sodium bicarbonate)?