Using Standard Curve to solve for Unknown Concentration

Once you create a standard curve from our lab data, you will use the equation to solve problems. In this example, once solved, the unknown concentration would work out to 0.395 M

[@soniasaini1388]

y axis= abs and x axis= conc.

[@NicholeRojas-r8i]

Thank you very much! I was complicated everything by using the axis in the opposite way 😅

[@muhammadshahnawazkhan5440]

Not me fascinated by hus board lol

[@rawanmhawe4145]

Concentration is the independent variable and should be on the x-axis; absorbance is the dependent variable and should be on the y-axis. That's what I have been taught in university.

[@floralscraft]

Sir,I didn't see u calculating for x , so how did u get it?

[@danielaochoa5706]

X is given. It is the absorbance value for the unknown.

[@TheJoshtheboss]

Why does every single other video have the axes other way round?...

[@realizedthinkit-makeit6136]

They have the axis switched because when you set up a Regression Analysis the dependent and independent variables have assigned axis. We are not trying to determine if there is a relationship between absorbance and concentration. Beer’s Law establishes this to be true. We are trying to use absorbance to find concentration of an unknown from its absorbance. If your use the equation I set up, or spend the time to graph with reversed axis and then rewrite the equation to solve for concentration (x in that case), you will end up with the exact same answer.

[@TheJoshtheboss]

@@realizedthinkit-makeit6136 Yes but for the law to be applied you need constants/coefficients against standards of known concentration first, before you can work out the concentration of unknowns.

[@TheJoshtheboss]

@@realizedthinkit-makeit6136 I have tried both approaches. The values are not the exact same.
Well, in my results they are up to 2 decimals. After that they start to differ, particularly with higher numbers or 2nd degree polynomials.
I am not sure if this approach would be accurate enough for GMP work, where traditional regression is used, with flipping the equation when solving for X

[@biologybrainery]

@@TheJoshtheboss Hi Josh. Thanks for the comments. It may lead to variance when extreme accuracy is necessary but in our case it is used in a 100-level BIO course where many students struggle to calculate mean and standard deviation. So, to find concentration of a unknown protein in a lab to introduce spectrophotometry and to get the basics of the concept, this works well. If it were for a 400-graduate level course, they would need to do the extra math.

[@TheJoshtheboss]

@@biologybrainery thanks for the clarification.

[@shahnazsarwon7825]

Can you please explain to us instead of explaining to yourself