Question

A compound with molecular mass 292.16g/molwas dissolved in a 5 - mLvolumetric flask. A1.00 - mLaliquot was withdrawn, placed in a 10 - mLvolumetric flask, and diluted to the mark. The absorbance atwas in 0.427 i acuvet. The molar absorptivity at 340nm is${\mathbf{\epsilon }}_{\mathbf{340}}\mathbf{=}\mathbf{6130}{\mathbf{M}}^{\mathbf{-}\mathbf{1}}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$

(a) Calculate the concentration of compound in the cuvet.

(b) What was the concentration of compound in the 5 - mL flask?

(c) How many milligrams of compound were used to make the 5 - mLsolution?

Short answer

a) The concentration of compound in the cuvet$\mathrm{c}=6.97.{10}^{-5}\mathrm{M}$

b) The concentration of compound in the 5 - mL flask$\mathrm{c}=6.97.{10}^{-4}\mathrm{Mc}$

c) The milligrams of compound used to make the 5 - mL solution m = 1.02mg

Step-by-step solution

Define concentration

The concentration of a substance is the quantity of solute presentin a given quantity ofsolution. Concentrations are usually expressed in terms of molarity, defined as the number of moles of solute in 1 L of solution.

Concentration of compound

Diluted 10 times

$\mathrm{c}=6.97.{10}^{-4}\mathrm{M}$

Concentration in Milligrams

$$\begin{gathered} \mathrm{n}=3.48.{10}^{-6}\mathrm{mol} \\ \mathrm{Mass} \\ \mathrm{m}=\mathrm{n}.\mathrm{M}=3.48.{10}^{-6}\mathrm{mol}.292.16\mathrm{g}/\mathrm{mol} \\ \mathrm{m}=1.02\mathrm{mg} \end{gathered}$$