Why must your line intersect the origin of the graph ( zero concentration equals zero absorbance)? Explain
The origin is a known point, because it is not possible to have zero absorbance with non-zero concentration and vice versa.
If the straight line has good correlation but does not pass through the origin, a systematic error would be suspected, such as calibration of instrument, etc.
Well, think of it this way - if the line didn't intersect the origin, that would mean that even with zero concentration, we would still have some absorbance. That would be quite the anomaly! We'd be dealing with some sort of magical substance that absorbs light even when it's not there. I mean, I've heard of invisible ink, but invisible absorbance? That's a whole new level of optical wizardry! So, to avoid creating a parallel universe of nonexistent substances, it's just much simpler and more logical to have the line intersect the origin, where zero concentration equals zero absorbance.
In order to understand why a line representing a relationship between concentration and absorbance must intersect the origin of a graph, we need to consider the underlying principles of the relationship between these two variables.
The relationship between concentration and absorbance is described by the Beer-Lambert Law, which states that there is a linear relationship between the concentration of a chemical species and the absorbance of light by that species. According to this law, the absorbance (A) is directly proportional to the concentration (C) and the path length (l) of the sample through which the light is passing, and is mathematically expressed as A = εcl, where ε is the molar absorptivity (also known as the molar extinction coefficient) which represents the efficiency of the species at absorbing light.
When we plot the absorbance values against corresponding concentration values on a graph, the resulting line represents the relationship between these variables. The slope of this line is determined by the product of molar absorptivity (ε) and path length (l), while the y-intercept represents the absorbance when the concentration is zero.
Therefore, if we have zero concentration of the species we are measuring, it logically follows that there should be zero absorbance as well. This is because in the absence of the species, there is nothing to absorb the light, resulting in no absorbance. Consequently, the line representing the relationship between concentration and absorbance must intersect the origin of the graph to reflect this fundamental principle: zero concentration equals zero absorbance.
In order to understand why the line in a graph of concentration versus absorbance must pass through the origin (zero concentration equals zero absorbance), we need to consider the principles behind the relationship between concentration and absorbance.
The relationship between concentration and absorbance is governed by the Beer-Lambert Law, which states that the absorbance of a sample is directly proportional to the concentration of the solute in the sample. Mathematically, it can be expressed as:
A = ε * c * l
Where:
A = Absorbance
ε = Molar absorptivity (a constant for a given substance at a specific wavelength)
c = Concentration of the solute
l = Path length (typically the width of the cuvette or the distance the light travels through the sample)
From this equation, we can see that the absorbance is directly proportional to the concentration. If the concentration is zero, then according to the equation, the absorbance should also be zero.
When creating a graph of concentration versus absorbance, the data points for different concentrations are plotted. The slope of the resulting line represents the molar absorptivity (ε), and the intercept of the line on the y-axis represents the absorbance at zero concentration.
Now, since the absorbance is expected to be zero at zero concentration, the line in the graph must intersect the origin (0, 0). This is because when concentration is zero, absorbance should also be zero according to the Beer-Lambert Law equation.
Therefore, it is necessary for the line to pass through the origin in order to accurately represent the relationship between concentration and absorbance, and to correctly account for the behavior of the system at zero concentration.