In recent years, the generation of chemical waste in educational institutions is being much discussed. For example, solid silver chloride residues can be reused in
teaching laboratory using them to oxidize formaldehyde thus recovering silver. The method
recovery of silver from the AgCl residue consists of the reaction of the AgCl(s) with
aqueous sodium hydroxide and formaldehyde under agitation for 10 minutes at 60°C.
Data: The amounts of reagents placed to react are:
1 g solid AgCl
25 mL NaOH 0.82 mol/L solution
0.6 mL formaldehyde 37% (m/m, percentage by mass)
The balanced chemical equation of the process of obtaining silver granules is:
2AgCl(s) + 3NaOH(aq) + CH2O(l) • 2 Ag(s) + HCO2Na(aq) + 2NaCl(aq) + 2H2O
Substances NaOH and CH2O are in excess. The amount of silver atoms recovered in the
process is:
data:
Molar masses (g/mol); Ag = 108; Cl = 35.5
Avogadro Constant: 6.00 × 1023
a) 376 × 1019 atoms.
b) 418 × 1019 atoms.
c) 627 × 1019 atoms.
d) 752 × 1019 atoms.
e) 836 × 1019 atoms.