Lab 7 – Spectrophotometry Notes (BIOL-1406)

These flashcards cover key concepts related to spectrophotometry, including terminology, procedures, and key outcomes from the lab.

What does a spectrophotometer measure?

It measures how much light a solution absorbs.

What is Beer’s Law?

Absorbance goes up as concentration goes up (direct relationship).

What is absorbance (A)?

It is the amount of light that a solution absorbs.

What does transmittance (%T) represent?

It is the percent of light that passes through a solution.

How is transmittance calculated?

%T = (light through ÷ total light) × 100.

What is a standard curve?

A graph of absorbance vs known concentrations used to find unknown concentrations.

What is the purpose of blanking a spectrophotometer?

To set the machine to ignore the solvent so it only measures the chemical.

What is a cuvette?

A small clear container for holding the solution while measuring.

What does Amax (λmax) indicate?

It shows the color (wavelength) that the solution absorbs the most.

What is dilution?

Making a solution weaker by adding more solvent, usually water.

How are food dyes identified using a spectrophotometer?

By checking their Amax (wavelength) against known dye values.

What is the λmax for Yellow #5 (Tartrazine)?

428 nm.

What happens if a dilution is incorrect?

The standard curve will be off, leading to wrong results for unknowns.

What should be avoided when handling cuvettes?

Handling cuvettes by the sides and avoiding fingerprints that block light.

What is measured in part 2 of the lab with methylene blue?

The absorbance at approximately 635 nm.

Why is it important to create a standard curve?

To link absorbance values to concentrations for unknown solutions.

What color absorbs UV light between 240-300 nm?

Proteins & DNA.

What is the purpose of measuring absorbance from 340–1000 nm?

To identify the maximum absorbance wavelength (Amax) for dyes.

What happens if the spectrophotometer is not blanked properly?

It could lead to inaccurate measurements of the absorbance.

Which color (wavelength) absorbs the least in the provided example?

Yellow (Amax = 427 nm).