# Beer Lambert Law: Solving Qs for Pharmacy Students

• UKstudent
In summary, the pharmacy student has forgotten how to answer questions on Beer Lambert's law. He would be grateful if anyone could show him how to answer these questions.
UKstudent
Hi, I'm an pharmacy student and I've forgotten how to answer questions on the beer lambert law. I would be grateful if anyone could show me how to answer these questions below.

(a)In pharmaceutics it is usual to use the specific absorption coefficient A (1%, 1 cm). What is this term?
(2 marks)

(b)The A(1%, 1cm) value for paracetamol in 0.1M sodium hydroxide is 715 at a wavelength of 257 nm. Calculate the concentration in μg/ml of a solution of paracetamol in 0.1M sodium hydroxide which gives an absorbance of 0.9 in a cell of pathlength 1 mm.
(6 marks)

(c)The concentration calculated in part (b) was as a result of a sample taken at 45 minutes from a dissolution test of a conventional release 500 mg paracetamol tablet. The volume of the dissolution medium was 900 ml. Calculate the amount of paracetamol (in mg) dissolved in the vessel and the percentage released from the 500 mg paracetamol tablet.
(4 marks)

Many thanks!

Beer-Lambert's law, if I remember correctly, is A=$$\epsilon$$lc, where A is absorbance, $$\epsilon$$ is absorption cross-section, l is path length, and c is concentration.

Yep, you're correct. Any ideas on which numbers to plug in into that equation?

Those given in the questions.

LOL. so tell me then, what would be my A, L,E and concentration values.

Have you actually read the question, or are you just hoping someone will do it for you? Some parameters are given explicit values and are called identical in both your post and kldickson's post. Other may require a little bit of tinkering, but they are all there.

--

See that’s the thing. I’ve forgotten completely how to answer questions like this. My book doesn’t explain it and neither is it in the lecture notes. So I would plug these values into the equ:
A= lc

0.9=0.1c

so 9=c….at which point I doubt my answer.

Moles=mass/conc

So 0.1= 151/c
So c=1510
And at this point I know I’ve missed out a step or am making stuff up. Just really confused.

What are you plugging in for equations B and C?

## 1. What is the Beer Lambert Law?

The Beer Lambert Law, also known as the Beer-Lambert-Bouguer Law, is a mathematical relationship that describes the absorption of light by a sample. It states that the absorbance of a solution is directly proportional to the concentration of the absorbing species and the length of the light path through the solution.

## 2. Why is the Beer Lambert Law important for pharmacy students?

The Beer Lambert Law is important for pharmacy students because it helps them understand the relationship between the concentration of a drug and its absorbance. This is crucial for determining the amount of drug present in a solution, which is necessary for accurate dosing and drug effectiveness.

## 3. How is the Beer Lambert Law used in pharmacy practice?

The Beer Lambert Law is used in pharmacy practice for various purposes, such as determining the concentration of a drug in a solution, monitoring drug levels in the body, and evaluating the purity of a drug sample. It is also used in spectrophotometry, a common technique used in pharmaceutical analysis.

## 4. What are the limitations of the Beer Lambert Law?

The Beer Lambert Law assumes that the solution being measured is dilute and has a uniform composition. It also assumes that the absorption of light is only caused by the target species and not by other factors. These assumptions may not hold true in all cases, leading to inaccurate results.

## 5. How can pharmacy students apply the Beer Lambert Law in real-world scenarios?

Pharmacy students can apply the Beer Lambert Law in real-world scenarios by using spectrophotometric techniques to determine the concentration of a drug in a solution, verifying the purity of drug samples, and monitoring drug levels in the body. They can also use the law to understand the factors that affect drug absorption and develop more effective drug delivery methods.

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