Question

iron(iii) thiocyanate spectroscopy
iron in solution
the unknown sample of fescn²⁺ has a
concentration of 0.0362 m. the percent
composition of iron in the complex ion is
49.0%.
how many iron atoms are in 100.0 ml of
0.0362 m fescn²⁺?
1.07 x 10²¹ atoms
0.00362 atoms
2.18 x 10²¹ atoms
3.62 atoms

Explanation:

Step1: Convert volume to liters

$100.0\ \text{mL} = \frac{100.0}{1000} = 0.1000\ \text{L}$

Step2: Calculate moles of $[FeSCN]^{2+}$

$\text{Moles} = \text{Molarity} \times \text{Volume} = 0.0362\ \text{mol/L} \times 0.1000\ \text{L} = 0.00362\ \text{mol}$

Step3: Relate moles of Fe to complex

1 mole $[FeSCN]^{2+}$ contains 1 mole Fe, so moles of Fe = $0.00362\ \text{mol}$

Step4: Calculate Fe atoms using Avogadro's number

$\text{Atoms} = 0.00362\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol} \approx 2.18 \times 10^{21}\ \text{atoms}$

Answer:

2.18 x 10²¹ atoms