Respuesta :
The molarity is 0.018M and the percentage is 8.46%.
Net ionic reaction is
[tex]$\mathrm{Cr} 2 \mathrm{O}^{2-}+6 \mathrm{Fe}^{2+}+14 \mathrm{H}^{+} \rightarrow 6 \mathrm{Fe}^{3+}+2 \mathrm{Cr}^{3+}+7 \mathrm{H} 2 \mathrm{O}$[/tex]
[tex]$1 \mathrm{~mol}$[/tex] of [tex]$\mathrm{Cr} 2 \mathrm{O} 7(-2)$[/tex] reacts with [tex]$6 \mathrm{~mol}$[/tex]of [tex]$\mathrm{Fe}(2+)$[/tex] to form [tex]$6 \mathrm{~mol}$[/tex]of [tex]$\mathrm{Fe}(3+)$[/tex] and [tex]$2 \mathrm{~mol}$[/tex] of [tex]$\mathrm{Cr}(3+)$[/tex]
Find molarity of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7$[/tex]
Molarity = moles of[tex]$\mathrm{K} 2 \mathrm{Cr} 207 /$[/tex] Volume of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7(\mathrm{~L}$[/tex] )
Moles of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7$[/tex] = grams of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7 /$[/tex] molar mass of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7$[/tex]
[tex]$=1.2275 \mathrm{~g} / 294.19 \mathrm{~mol}=0.0042 \mathrm{~g} / \mathrm{mol}$[/tex]
Molarity of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7=$[/tex] moles of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7$[/tex]/ Volume of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7$[/tex](L)
[tex]$=0.0042 \mathrm{~g} / \mathrm{mol} / 0.250 \mathrm{~L}=0.017 \mathrm{M}$[/tex]
Find molarity of [tex]$\mathrm{Fe}$[/tex] (II)
Molarity of [tex]$\mathrm{Fe}(\mathrm{II})=6 \times$[/tex]molarity of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7 \times$[/tex]volume of [tex]$\mathrm{K} 2 \mathrm{Cr} 2 \mathrm{O} 7 /$[/tex]volume of [tex]$\mathrm{Fe}$[/tex] (II)
[tex]$=6 \times 0.017 \mathrm{M} \times 0.03598 \mathrm{~L} / 0.200 \mathrm{~L}$[/tex]
[tex]$=0.018 \mathrm{M}$[/tex]
Find moles of [tex]$\mathrm{Fe}(\mathrm{II})$[/tex]
Moles of [tex]\mathrm{Fe}($ II) =[/tex]molarity of [tex]$\mathrm{Fe}$[/tex] (II) [tex]$\times$[/tex] volume of [tex]$\mathrm{Fe}$[/tex] (II)
[tex]=0.018 \mathrm{M} \times 0.200 \mathrm{~L}=0.004 \mathrm{~mol}[/tex]
Find mass of Fe(II)
Mass of [tex]\mathrm{Fe}( II )=[/tex] moles of [tex]\mathrm{Fe}( II[/tex]) [tex]\times[/tex] molar mass of [tex]$\mathrm{Fe}(\mathrm{II})$[/tex]
[tex]$=0.004 \mathrm{~mol} \times 55.85 \mathrm{~g} / \mathrm{mol}$[/tex]
[tex]$=0.205 \mathrm{~g}$[/tex]
Find [tex]$\% \mathrm{Fe}(\mathrm{II})$[/tex] in unknown sample
[tex]$\begin{aligned}\% \mathrm{Fe} &=(\text { mass of } \mathrm{Fe} / \text { weight of unknown sample }) \times 100 \\&=(0.205 \mathrm{~g} / 2.4234 \mathrm{~g}) \times 100 \\&=8.46 \%\end{aligned}$[/tex]
- Molarity is the concentration of a solution expressed as the number of moles of solute dissolved in each liter of solution.
- concentration is the amount of a substance per defined space. Concentration usually is expressed in terms of mass per unit volume.
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