Answer:
0.05 mM
Explanation:
NiCl_2(aq) + 2AgNO_3 (aq) -------> 2 AgCl (s) + Ni(NO_3)_2 (aq)
Molar mass of NiCl_2 = 129.5994 g/mol
Molar mass of AgNO_3 = 169.87 g/mol
Molar mass of AgCl = 143.32 g/mol
The chemist added 58mM of silver nitrate = 58 / 1000 = 0.058 M
mass of silver nitrate present =0.058 × 169.87 = 9.85246 g
according to the equation of reaction
2 mole of silver nitrate is needed to produce 2 mole of silver chloride
2 mole of silver nitrate = 339.74 g
2 mole of silver chloride = 286.64 g
339.74 g silver nitrate produces 286.64 g silver chloride
unknown mass of silver nitrate produce 0.0036 g
unknown mass of silver nitrate = 339.74 × 0.0036 / 286.64 = 0.00427 g
then
1 mole of NiCl_2 reacts 2 mole of AgNO_3
129.5994 g of NiCl_2 react with 339.74 g AgNO_3
unknown mass of NiCl_2 react with 0.00427 g AgNO_3
mass of NiCl_2 = 0.00163 g
mole of NiCl_2 present = 0.00163 / 129.5994 = 0.0000126 mole
Molarity = 0.0000126 mole / 0.25 L = 0.0000504 M = 0.05 mM