Which of the following statements is incorrect about Beer\'s Law. A = epsilon cb

Question

Which of the following statements is incorrect about Beer's Law. A = epsilon cb? a) A is the absorption or the reading of absorbance; b) t is called the molar extinction coefficient (epsilon); c) c is the molarity of the absorbing species; d) b is the path length of light through the sample; e) Beer's Law is applicable only to visible lights. Answer How many grams of CuSO_4 5H_2O are needed to prepare 50.0 mL of a 0.300 M CuSO_4 solution? (Molar mass of CuSO_4 5H_2O = 249.7 g/mol) (iii) If 2.00 mL of the 0.30 M CuSO4 solution is diluted to 5.00 mL with water, what is the resulting CuSO_4 concentration? (IV) At a wavelength of 270 nm. a 0.040 M solution of acetone in water has an absorption of 0.64 in a 1.00 cm cell The absorption of a solution of unknown concentration of acetone in water was 0.48 at the same wavelength and in the same cell. What is the concentration of acetone in the unknown? (Assume that there is zero absorption of light by water at 270 nm.)

Explanation / Answer

i) e) Beer's law is applicable only to visible light ( This is incorrect for beer lambert's law).

ii) Molarity = moles / Ltr of solution.

0.3 M = moles / 0.050 Ltr

moles = 0.3 mol/Ltr x 0.050 Ltr = 0.015 moles.

0.015 moles = 249.7 g/mol x 0.015 moles = 3.75 g of CuSO4 . 5H2O are needed to be dissolved in 50 mL

iii) V1M1 = V2M2

M2 = 2 mL x 0.3 M / 5 mL = 0.12 M

iv) step 1 : find E value in A = ECl , A = 0.64, C = 0.04 M, l = 1 cm

E = 0.64/(0.04 x 1) = 16.

step 2 : find the C value by using E = 16

0.48 = 16 x C x 1

C = 0.03 M

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