Spectrophotometry and Beer's Law
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- Опубліковано 4 вер 2019
- We've learned about kinetics already, but how do we gather kinetic data? One clever method is by analyzing how the color of a solution changes over time, which is an indication of the concentration of certain compounds that interact with light in a specific way. This technique is called spectrophotometry, and this type of analysis will involve calculations using Beer's Law. Let's take a closer look!
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Yes 😀
Beer's law?
Aye, I'll drink to that.
*Beer Lambert Law*
Me too
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Hi Scoot Beer. My name is not Scott Beer.
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Hi Dave, since A is log (I/I0) and A is e*b*c, then I = I0 * 10^(-ebc), not I0*exp(-ebc) because it is not a natural logarithm but a base 10 logarithm.
Wow I was just lectured about this in chem and now studying for the midterm in 2 days what’re the odds hell yes professor dave
Very well explanation. Now I get the idea what this is all about🙏🏻
Thank you for this well-explained video !
thanks professor dave! This helped reiterate what my online course just blew through rather quickly
Hi professor.
I always learn something from your channel.
Very clear explanation. thanks prof Dave
Thanks a lot... you make the topic easy to understand.
Thank you so much for the explanation!
My professor used the example as an activity for the class but she asked which compound the measurement belongs to and I have no idea how to determine that.
Just shared the video with a friend who didn't understand wery well what they did just today at chemistry class😉
One of the best channels in the field
Could you give me a name of software where I can plot my graph in better way?
Thank you professor Dave I have got relevant notes
Thanks for your video, Professor Dave! one thing to mention, it might better to tell log used here is actually base with e, not 10. In context it explained greatly, but itself I got bit confused for secs.
Why is the number of moles a concentration? Isnt the concentration moles/volume? How can i get the total number of moles in the cuvet?
Nice first like and Comment! Loving your channel Bro, I always learn something from you 👌🏻👍🏻😁😎
On the example why is the initial intensity 1, where did that 1 came from??
I love being able to understand something!
thanks professor dave really helpful
Is the value of incident light always taken as 1?
Thank you professor David for this video.
Please professor Dave, why do you use Iø as 1?
You are easily better than my chem lab ta. Thank you.
Ps. I like the new haircut.
Thanks for your helpful videos
Very useful. Thank you.
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Hi professor
Could you do a video about asanning electron microscop plz
Sir can u pls give a lecture about calorimeter principles and its application..
Can you do one for thin layer chromatography? Would be greatly helpful!
how 0.35 came for molar absorptivity?
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Thanks a lot professor...
For a part of my project, I was thinking about making a standard curve type thing, like make a range of dilutions and then plot the absorbance against the dilution concentration and then have the computer put a line of best fit. Then any sample I run with that substance I can just plug it into the graph. Would that give me a fairly accurate concentration? Would the concentration vs absorbance be linear? Thanks
It depends on several factors, but perhaps most importantly whether you are below, I believe, 1 ABS. Around ABS>1, the correlation becomes nonlinear. You may also have to account for variables such as temperature change and material properties. The spectrometer i use has water cooling and a temperature controller, but I doubt most have that 🤔
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Is “log” log base ten? Because i usually see people use “Log” or “ln” for natural log.
yep if the base is not specified it's implied to be 10
@@ProfessorDaveExplains Also, in our experiments, we took the logarithmic as 10 instead of e.
Do you think sir, it's a good idea to create a spectrophotometer using specific wavelength only? For water analysis?
seems like an arbitrarily limitation to me
@@ProfessorDaveExplains can you explain further?
By the way sir, I conducted some experiment using pasco spectrometer, i see that at 650nm wavelength the water absorbance of a distilled water is 0 , that's why i'm thinking to use 650nm as a standard source of light to determine the impurity of water
@@vicentesayson2990 anything would do right? light absorved same?
easy understand. tq sir
Hi professor Dave, I realized that you convert the log with a base of 10 to a exponential with a base of e, shouldn't it be in the base of 10? or else a natural log should be used instead of log in the base of 10
I also thought the same
It's unfortunate and rather annoying but some textbooks and professors use log to mean "log base e", while others use it to mean "log base 10". It makes sense to just call log base e "log" if you know where the logarithm operation originally came from, but it's confusing nonetheless
@@GameHero531 so basically he meant log base e (ln) not log base 10?
(the terminology is a bit new so just clarifying :))
@@CMThota correct
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What was it about bonding? It wasn’t explained
Hearing all these numbers made me anxi😢us about my homework so maybe I'll watch the rest another time
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Can you teach us how to make beer from a chemist's perspective?
This relate with physics or biology???
Can someone point out the following:
If Transmittance is defined as I/I0, then why isn't Absorbance defined as A=1-T , but rather as A=-log(T)?
What does then 1-T signify? The percentage of light that doesn't get transmitted which is not the absorbance?
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How is the path length selected?
it's the length of the cuvet
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Should that not be Ln and not Log(10) ? If A = Ln (1/0.12) = 2.12, that gives c=3.03M If you put c=3.03M into the exponential function, then the absorption is 0.12 as given in the example.
It doesn't matter which logarithm base one uses (natural logarithm of base e or logarithm of base 10, the latter of which is most common for absorbance), the result will still be consistent with the formulae.
Here's the logarithm of base 10 calculation step by step:
1. .9208/(.35*2)=1.3154285714285714
2. 1.3154285714285714*2*.35=0.9208
This is what's shown in the video at 4:58.
From 'en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law', uppercasing the important parts: '''It correlates the absorbance, MOST OFTEN EXPRESSED as the negative DECADIC logarithm of the transmittance'''.
I'll look at that again, thanks! I also noticed that there are only 2 significant figures given in the example...
If you go to 3:41 there are two expressions one using Log (base 10) and the other is an exponential function i.e. Ln or log to base e. If you put the values for e, b and c into the exponential function you get I/Iº = 0.3897, not 0.12 as shown later. It looks like two types of logs have been mixed up.
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Um, yes, I am Professor Dave. The channel is called Professor Dave Explains. See?
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Thank you
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I'm confused how did we go from log I/i0, to e to the power of
stuff?? Should it have been ln I/i0?????
I think he made a mistake he mistook log(I/i0) with ln(I/i0).
it should have been
I = i0* 10^-(epsilon*b*c)
Hello, thank you for your videos - I show them to my undergraduate chemistry classes on occasion. However, there is an error in this video - the opposite of log is 10^x not e^x
e^x is a notation for 10 to a power
@@kamilewais-orozco9971 Mathematically, that makes absolutely no sense. But so be it.
John Cavanaugh it doesn’t, but it’s helped me sort it out in my head
log(x) is ambiguous and can be used to represent both base e and base 10. It is exceedingly common to use it as base e in physics.
@@kamilewais-orozco9971 e is a special constant appearing in nature
Thanks 🌸
Dave, are you considering making computer science lectures?
yes definitely one day!
Anyone else have a broken Spec 20 for lab?
Hey professor can you explain on how to calculate percentage transmittance. please😊
Absorbance = 2 - log_10(%T)
Example:
1 = 2-log_10(T)
T = 10%
Good vedio ♥️
Verification of beer lambert law through colorimetric
Beer's law? Drink it.
Help with a question ????? A compound absorb light in 227 nm. The standard curve calibration for the compound is Abs = 372x + 0,6432 which the concentration is g/100mL. The technique was analytical standard adding from fluoxetine hydrochloride (C17H18F3NO.HCl - molar mass = 345,79 g/mol). So determine the concentration in mol/L from the analysed solution. Show all calcs progression.
Thanks
Thanks..
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nice cut
Please how did our I become 1?
Good
2:50
PROF. DAVE LANG MALAKAS (in filipino-only prof.dave is strong)
I like the look
can please someone do a remix of the intro. I am talking 24h version
I'm August beer and i approve this video
3:18 I got lost here
ua-cam.com/video/wxrAELeXlek/v-deo.html at around 2:35 he visualizes that and it made sense
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👍
Beer Lambert's Law
When it says log, I guess that's the natural log, ln.
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It is tough 🙁
This would have been useful 3 months ago, when i was actually seeing this shit in college
Plotting in real time with a computer? That’s just code for “undergrads”.