Question

need help with Concentration solutions

Determine the Cu?molar concentration of each unknown solution. For unknown Cu? solution 1, the absorbance = 0.176 at 675 nm. Unknown Cul solution 1 concentration = _м For unknown Cu? solution 2, the absorbance =0.827 at 675 nm. Unknown Cu? solution 2 concentration - M

Answer 1

• here we will apply beer lambert law : which is:

A = Ɛ C l       i)

where A is the absorbance ( no units)

Ɛ is molar absorptivity coefficient ( units are L mol-1 cm-1)

C is the concentration of sample ( units are mol L-1 )

And l is the path length of the sample in cm

• Now, from the graph we get trendline y = mx + b

Where m ( slope) = 4.089

Intercept b = 0.005748

Therefore , y = 4.089x + 0.005748 ii)

y-0.005748 = 4.089 x                                                                                                        iii)

Comparing with equation i)

We get,

absorbance = y

concentration = x , l = 1 cm

and Ɛ = 4.089

• for unknown Cu+2 solution 1 , absorbance y = 0.176

concentration C= ?

putting values in equation iii)

0.176-0.005748 = 4.089 x concentration

Concentration = 0.0416 M

• for unknown Cu+2 solution 2 , absorbance y = 0.827

concentration C= ?

putting values in equation iii)

0.827-0.005748 = 4.089 x concentration

Concentration = 0.2008 M