Question

PLEASE explain Spectrophotometry and what is soo important about 400nm

PLEASE explain how absorbance and beer's law relate

Relate Beer’s law to the equation of a line on a standard curve.

Why is the line forced through zero on the standard curve?

What does the R2 value for the graph says about the experiment?

Answer 1

Spectrophotomtery: Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution. The basic principle is that each compound absorbs or transmits light over a certain range of wavelength. This measurement can also be used to measure the amount of a known chemical substance. A spectrophotometer is an instrument that measures the amount of photons (the intensity of light) absorbed after it passes through sample solution. With the spectrophotometer, the amount of a known chemical substance (concentrations) can also be determined by measuring the intensity of light detected.

400nm is important: 400nm is at the verge of both ultraviolet range (185 - 400 nm) and visible range (400 - 700 nm) of electromagnetic radiation spectrum.This helps in analyzing a great number of samples.

Relation of absorbance and Beer's Law: Beer-Lambert Law (also known as Beer's Law) states that there is a linear relationship between the absorbance and the concentration of a sample. For this reason, Beer's Law can only be applied when there is a linear relationship. Beer's Law is written as:

A=?lc

where A is the measure of absorbance (no units), ? is the molar extinction coefficient or molar absorptivity (or absorption coefficient), l is the path length, and c is the concentration. The molar extinction coefficient is given as a constant and varies for each molecule. Since absorbance does not carry any units, the units for ? must cancel out the units of length and concentration. As a result, ? has the units: L