Pre-lab Questions For Experiment #7 ecb? (1) Which of the following statements i

Question

Pre-lab Questions For Experiment #7 ecb? (1) Which of the following statements is incorrect about Beer's Law, A a) A is the absorption or the reading of absorbance b) s 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: (2) An unknown concentration of NiSO4 solution is to be determined by colorimetric analysis using a spectrophotometer. The standard solutions are prepared as the following: 2.00 mL (the same procedures for 3.00 mL 4.00 mL, 6.00 mL 7.00 mL) of the stock solution of 1.00 M NiSO is transferred into a 25-mL volumetric flask and diluted by adding distilled water to the mark line. The spectrophotometer is calibrated at the wavelength of 635 nm. The absorbance (A) readings and the concentrations of these standard solutions are tabulated Volumes of Concentrations of Absorbance the Stock Solution 173 2.00 3.00 4.00 6.00 the standard solutions (M) 0.132 0.198 0.264 0.390 458 a) Calculate the concentrations of the standard solutions and complete the column 2 in the above table b) On the graph paper provided below, plot the standard concentrations (independent variables) versus the absorbance readings (dependent variables) and draw the best-fit straight-line for all the data points. c) If the unknown absorbance is 0.250, what is the concentration of the unknown? d) If the unknown absorbance is 0.950, suggest a method for obtaining the concentration of the unknown.

Explanation / Answer

Beers Law: The mount of energy absorbed or transmitted by a solution is proportional to te solutions molar absorptivity and the concentrate of solute.

A = bc
where, A = Absorbtion

   = Molar extintion coefficient

c = Concenration of solution

b = Path length

Beers law applicable not only visible light sample,whcih is applicable all liquid samples at low concentrations.

Answer : e

Beers law is capable of describing absorption behavior of solutions containing relatively low amounts of solutes dissolved in it (<10mM). When the concentration of the analyte in the solution is high (>10mM), the analyte begins to behave differently due to interactions with the solvent and other solute molecules and at times even due to hydrogen bonding interactions.

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