Answer
Mass percentage of nitrate = 67.74%
Explanation
Number of moles of cobalt nitrate = 1.56 moles
Mass of the cobalt nitrate = 2.85 x 10⁵ mg
First, convert 2.85 x 10⁵ mg cobalt nitrate to gram
1 mg = 10⁻³ g
Therefore, 2.85 x 10⁵ mg cobalt nitrate = 2.85 x 10⁵ x 10⁻³ = 2.85 x 10² grams
This implies;
1.56 moles of cobalt nitrate → 2.85 x 10² grams cobalt nitrate
1 mole will contains;
[tex]\frac{2.85}{1.56}\times10^2=1.8269\times10^2\text{ grams cobalt nitrate}[/tex]Note: Irrespective of oxidation number of cobalt, its molar mass is the same.
Molar mass of cobalt = 58.933193 g/mol
Therefore, the mass of nitrate in the content = (182.69 - 58.933193) = 123.756807 g
[tex]\begin{gathered} Mass\text{ percentage of nitrate }=\frac{\text{mass of nitrate}}{\text{mass of cobalt nitrate}}\times100 \\ Mass\text{ percentage of nitrate }=\frac{123.756807}{182.69}\times100 \\ Mass\text{ percentage of nitrate }=67.74\% \end{gathered}[/tex]