Answer:
percentage mass of platinum in the alloy ≈ 90.60 %
Explanation:
The alloy is 8.528 g sample of an alloy containing platinum and cobalt . The alloy react with excess nitric acid to form cobalt(ii) nitrate . Platinum is resistant to acid so it will definitely not react with the acid only the cobalt metal in the alloy will react with the acid.
The chemical reaction can be represented as follows:
Co (s) + HNO₃ (aq) → Co(NO₃)₂ (aq) + NO₂ (l) + H₂O (l)
The balanced equation
Co (s) + 4HNO₃ (aq) → Co(NO₃)₂(aq) + 2NO₂ (l) + 2H₂O (l)
Cobalt is the limiting reactant
atomic mass of cobalt = 58.933 g/mol
Molar mass of Co(NO₃)₂ = 58.933 + 14 × 2 + 16 × 6 = 58.933 + 28 + 96 = 182.933 g
58.933 g of cobalt produce 182.933 g of Co(NO₃)₂
? gram of cobalt will produce 2.49 g of Co(NO₃)₂
cross multiply
grams of cobalt that will react = (58.933 × 2.49)/182.933
grams of cobalt that will react = 146.74317000/182.933
grams of cobalt that will react= 0.8021689362 g
grams of cobalt that will react = 0.802 g
mass of platinum in the alloy = 8.528 g - 0.802 g = 7.726 g
percentage mass of platinum in the alloy = 7.726/8.528 × 100 = 772.600/8.528 = 90 .595 %
percentage mass of platinum in the alloy ≈ 90.60 %
