Answer:
The relative atomic mass of the metal is 207.2 u
Explanation:
Metal chromate
Given that;
1) The mass of fluorine is 14.96% of the metal fluoride
2) 2 Chromium are connected to the metal when the metal chromate, CrO²⁻, is formed
We have;
Number of ions available in the metal = Cr₂O₇²⁻ = +2 ionic
Molar mass of fluorine = 18.998 g/mole
Ionization of fluorine = -1
Number of moles of fluorine required per metal +2 ion= 2 moles
3) Number of moles of fluorine per mole of compound of the metal fluoride = 2 × moles
Mass of fluorine per mole of compound = 2 × 18.998 = 37.996 grams
Percentage by mass of fluorine = 14.96%
Fluoride
Let the mass of the compound = X
Therefore;
14.96% of X = 37.996 grams
X = 37.996/(0.1496) = 253.984 grams
Therefore the mass of the metal in the compound = 253.984 - 37.996 = Molar mass 215.99 grams
Given that the metal forms a chromate with 2 chromium atoms and a mass of 215.99 grams, the likely candidate is lead, Pb with a molar mass of 207.2 grams and a chromate of Pb(CrO₄)₂.
The fluoride, lead fluoride, F₂
The relative atomic mass of lead is 207.2 u
