Question

A chemist prepares a solution of iron(III) bromide (FeBr3) by measuring out 41.1 mg of FeBr3 into a 50. mL volumetric flask and filling to the mark with
distilled water.

Calculate the molarity of Br- anions in the chemist's solution

Be sure your answer is rounded to 2 significant digits.

Answer 1

Answer: The molarity of $Br^-$ anions in the chemist's solution is 0.0084 M

Explanation:

Molarity of a solution is defined as the number of moles of solute dissolved per liter of the solution.

$Molarity=\frac{n\times 1000}{V_s}$

where,

n = moles of solute

$V_s$ = volume of solution in ml

moles of $FeBr_3$ = $\frac{\text {given mass}}{\text {Molar mass}}=\frac{0.0411g}{295.6g/mol}=0.00014mol$

Now put all the given values in the formula of molality, we get

$Molarity=\frac{0.00014\times 1000}{50}=0.0028$

As 1 mole of $FeBr_3$ gives = 3 moles of $Br^-$

0.0028 moles of $FeBr_3$ gives = $\frac{3}{1}\times 0.0028=0.0084 moles$ of $Br^-$

Thus the molarity of $Br^-$ anions in the chemist's solution is 0.0084 M