Question

An experiment was performed under identical conditions as yours. The absorbance of the penny solution was recorded as 0.219 absorbance units. A calibration plot of absorbance vs. concentration of Cu(II) (M) yielded the following trendline equation:

y= 11.589x - 0.0002

Required:
What is the concentration (mol/L) of the penny solution?

Answer 1

Answer:

Concentration C = 0.0189 mol/L

Explanation:

From the given information:

Let consider the formula used in calculating the concentration according to Beer's law:

$\mathtt{A =\varepsilon \times L \times C}$ --- (1)

here;

A = absorbance

ε = coefficient of molar absorptivity

L = path length

C = concentration (mol/L)

Also, from Beer law plot:

y = mx+b

where,

y represent absorbance A

b represents intercept

m represents the coefficient of molar absorptivity ε

and x represents the concentration(C).

replacing the substituted entities

A = ε × C + b ---- (2)

Making the concentration the subject of the above formula:

$C = \dfrac{A-b}{\varepsilon}$----(3)

From y = 11.589x - 0.0002

A = 11.589 *C - 0.0002

Given that:

A = 0.219

∴

0.219 = 11.589 *C - 0.0002

0.219 + 0.0002 =  11.589 *C

C = 0.2192/11.589

C = 0.0189 mol/L