Concise Physical Chemistry

c13 JWBS043-Rogers September 13, 2010 11:27 Printer Name: Yet to Come

218 COULOMETRY AND CONDUCTIVITY

Problem 13.2

What is the charge on the silver ions in 1.000 dm^3 of dissolved Ag+in aqueous

solution equilibrium with Cl−and solid AgCl(s) at 298 K? The solubility product

constant of AgCl isKsp= 1. 77 × 10 −^5. There is no outside source of Cl−ion.

Problem 13.3

l-Dopa (l-(dihydroxyphenyl)alanine) is used to treat the symptoms of Parkinson’s

disease. It is quantitatively and exhaustively reduced in an electrolysis cell, requir-

ing two electrons per molecule. Its molar mass isM= 0 .1972 kg mol−^1. Suppose

a sample requires 57.5μC (microcoulombs) for complete reduction. How much

l-dopa was in the sample?

Problem 13.4

The resistivity of copper at 298 K isρ= 1. 71 × 10 −^8 ohm m. A potential of 1.00 mV

was placed across a copper wire 1.00 mm in diameter and 1.00 m long. What was the

current?

Problem 13.5

(a) The resistivity of copper at 298 K isρ= 1. 71 × 10 −^8 ohm m. Find the

conductance and the conductivity of a copper wire 1.00 mm in diameter

and 1.00 m long.

(b) Find the conductance and the conductivity of a copper wire 2.00 mm in

diameter and .500 m long.

Problem 13.6

A conductivity cell is constructed using two platinum electrodes, precisely machined

to be a square 2 cm on an edge and 1 cm apart. A 0.1000 mol dm−^3 HCl solution was

poured into the cell, and the resistance was measured and found to be 6.3882 ohms.

What is the molar conductivity of HCl at this concentration? In solving this problem,

be careful to express the units clearly at each step.

Problem 13.7

We can write the ionization of water in a somewhat simplified form as

H 2 O→H++OH−

The conductivity of deionized water isκ= 5. 50 × 10 −^6 ohm−^1 m^2 mol−^1.

(a) Find the concentrationcof pure water in mol dm−^3.

(b) Find the degree of ionizationα.