Silver chemistry is dominated by Ag (I) compounds. Compounds of silver in higher... Note: Use Ulat(A — Physical Chemistry Chemistry Question
High-valent silver compounds
Silver chemistry is dominated by Ag (I) compounds. Compounds of silver in higher...
Note: Use Ulat(AgIIO) = 3180.0 kJ·mol-1 and Ulat (AgIAgIIIO2) = 8310.0 kJ·mol-1 if you cannot calculate Ulat(AgIIO) in Part 3.8).
Choose the appropriate magnetic behavior of A if it exists as AgIIO.
Model Answer
Diamagnetic Paramagnetic
Assign the oxidation number of Ag1 and Ag2.
Model Answer
Oxidation number of Ag1 : ……….+1
Oxidation number of Ag2 : ……… +3
What is the coordination number of O atoms in the lattice of A?
Model Answer
The coordination number of O atoms = 3
How many AgI and AgIII bond to one O atom in the lattice of A?
Model Answer
Number of AgI = 1
Number of AgIII = 2
Predict the magnetic behavior of A. Check the appropriate box below.
Model Answer
Diamagnetic Paramagnetic
The AgI is d10 hence diamagnetic; the AgIII is square planar d8 also diamagnetic
The compound A can also be formed on warming a solution of Ag+ with peroxydisulfate. Write down the equation for the formation of A.
Model Answer
S2O82-(aq) + 2 Ag+(aq) + 2 H2O(l) → 2 SO42-(aq) + AgIAgIIIO2(s) + 4 H+(aq)
Calculate Ulat at 298 K of AgIAgIIIO2 and CuIIO. Assume that they are ionic compounds.
Model Answer
Ulat of AgIAgIIIO2:
ΔHlat(AgIAgIIIO2) = 2 ΔHf°(O2-) + ΔHf°(Ag+) + ΔHf°(Ag3+) – ΔHf°(AgIAgIIIO2)
= (2×249 – 2×141 + 2×844) + (284.9 + 737.2) + (284.9 + 737.2 + 2080.2 + 3367.2) – (–24.3) = +9419.9 kJ mol–1
Ulat(AgIAgIIIO2) = ΔHlat(AgIAgIIIO2) – 4 RT = +9419.9 – 10.0 = +9409.9 kJ mol–1
Ulat of CuIIO:
ΔHlat(CuIIO) = ΔHf°(O2–) + ΔHf°(Cu2+) – ΔHf°(CuIIO)
= (249 – 141 + 844) + (337.4 + 751.7 + 1964.1) – (–157.3) = 4162.5 kJ·mol–1
Ulat(CuIIO) = ΔHlat(CuIIO) – 2 RT = 4162.5 – 5.0 = 4157.5 kJ mol–1
Calculate Ulat for the hypothetical compound AgIIO. Assume that AgIIO and CuIIO have the same type of lattice, and Vm(AgIIO) = Vm(AgIIAgIII2O4) – Vm(AgIII2O3).
Model Answer
Vm(AgIIO) = Vm(AgIIAgIII2O4) – Vm(AgIII2O3) = 0.08985 – 0.06182 = 0.02803 nm3
From the relationship Ulat = C×(Vm)–1/3, Ulat(AgIIO) = 3733.6 kJ mol–1 [or 3232.9 kJ mol–1 if using Ulat CuIIO = 3600 kJ mol-1]
By constructing an appropriate thermodynamic cycle or otherwise, estimate the enthalpy change for the solid-state transformation from AgIIO to 1 mole of AgIAgIIIO2.
Model Answer
ΔHrxn = 2 Ulat(AgIIO) + 4RT + IE3 – IE2 – Ulat(AgIAgIIIO2) – 4RT
= 2 × 3733.6 + 3367.2 – 2080.2 – 9409.9
= – 655.7 kJ/mol (or -663.0 kJ/mol using given Ulat values)
Indicate which compound (AgIIO or AgIAgIIIO2) is thermodynamically more stable.
(Check the corresponding box.)
When AgIAgIIIO2 is dissolved in aqueous HClO4 solution, a paramagnetic compound (B) is first formed then slowly decomposes to form a diamagnetic compound (C). Given that B and C are the only compounds containing silver formed in these reactions, write down the equations for the formation of B and C.
Oxidation of Ag+ with powerful oxidizing agents in the presence of appropriate ligands can result in the formation of high-valent silver complexes. A complex Z is synthesized and analyzed by the following procedures:
An aqueous solution containing 0.500 g of AgNO3 and 2 cm3 of pyridine (d = 0.982 g cm-3) is added to a stirred, ice-cold aqueous solution of 5.000 g of K2S2O8. The reaction mixture becomes yellow, then an orange solid (Z) is formed which has a mass of 1.719 g when dried.
Elemental analysis of Z shows the mass percentages of C, H, N elements are 38.96%, 3.28%, 9.09%, respectively.
A 0.6164 g Z is added to aqueous NH3. The suspension is boiled to form a clear solution during which stage the complex is destroyed completely. The solution is acidified with excess aqueous HCl and the resulting suspension is filtered, washed and dried (in darkness) to obtain 0.1433 g of white solid (D). The filtrate is collected and treated with excess BaCl2 solution to obtain 0.4668 g (when dry) of white precipitate (E).
Model Answer
For C: 4 Ag(ClO4)2 (aq) + 2 H2O (l) 4 AgClO4 (aq) + 4 HClO4 (aq) + O2 (g)
Determine the empirical formula of Z and calculate the percentage yield in the preparation.
Model Answer
mol Ag in 0.6164 g of Z = mol of AgCl = 0.001 mol
mol SO4 2- from 0.6160 g of Z = mol BaSO4 = 0.002 mol
Mass percentage of Ag = 0.001×107.87/0.6164 = 17.50 %
Mass percentage of SO4 2- = 0.002×96.06/0.6164 = 31.17 %
From EA:
Ratio Ag2+ : SO42- : C : H : N = 1 : 2 : 20 : 20 : 4
Yield = 94.7 %
Ag (IV) and Ag (V) compounds are extremely unstable and found only in few fluorides. Thus, the formation of their complexes with organic ligands in water can...