# Question 93e3a

Apr 2, 2017

$M = \text{0.116 mol/L"; ["Fe"^"3+"] = "0.116 mol/L";["Br"^"-"] = "0.349 mol/L}$

#### Explanation:

Molarity

The molarity of a solution is given by the expression

color(blue)(bar(ul(|color(white)(a/a)"Molarity" = "moles"/"litres"color(white)(a/a)|)))" "

or

$M = \frac{n}{V}$

where

$M =$ molarity
$n =$ number of moles
$V =$ volume in litres

The molar mass of ${\text{FeBr}}_{3}$ is 295.56 g/mol.

 n = 12.9 color(red)(cancel(color(black)("g FeBr"_3))) × ("1 mol FeBr"_3)/(295.56 color(red)(cancel(color(black)("g FeBr"_3)))) = "0.043 65 mol FeBr"_3

V = 375 color(red)(cancel(color(black)("mL"))) × "1 L"/(1000 color(red)(cancel(color(black)("mL")))) = "0.375 L"

$M = \text{0.043 65 mol FeBr"_3/"0.375 L" = "0.116 mol/L}$

Concentration of $\text{Fe"^"3+}$

The equation for the solution process is

$\text{FeBr"_3(s) → "Fe"^"3+""(aq)" + "3Br"^"-""(aq)}$

We see that 1 mol of ${\text{FeBr}}_{3}$ gives 1 mol of $\text{Fe"^"3+}$.

["Fe"^"3+"] = (0.116 color(red)(cancel(color(black)("mol FeBr"_3))))/"1 L" × ("1 mol Fe"^"3+")/(1 color(red)(cancel(color(black)("mol FeBr"_3)))) = "0.116 mol/L"

Concentration of $\text{Br"^"-}$

We see from the chemical equation that 1 mol of ${\text{FeBr}}_{3}$ gives 3 mol of $\text{Br"^"-}$.

["Br"^"-"] = (0.116 color(red)(cancel(color(black)("mol FeBr"_3))))/"1 L" × ("3 mol Br"^"-")/(1 color(red)(cancel(color(black)("mol FeBr"_3)))) = "0.349 mol/L"#