H3 Chemistry: Plan quantitative analysis using UV/visible spectroscopy

Your success criteria

• Plan quantitative analysis using UV/visible spectroscopy
• Use named chemical evidence.
• Transfer the governing reason to an unfamiliar case.

Orientation and prerequisite retrieval

A calibration uses standards of known concentration measured under matched conditions.

A reagent blank establishes the baseline absorbance.

Explore this H3 topic and lesson sequence.

Definitions and exact language

The unknown should be measured at the same wavelength as the standards.

An unknown is interpolated within the linear calibration range rather than extrapolated far beyond it.

Detailed molecular explanation

Replicate standards and unknown readings help assess random variation.

A linear calibration has absorbance on one axis and concentration on the other with units stated.

Worked leaf-specific case

Any dilution factor applied before measurement must be reversed for the original concentration.

A volumetric pipette and volumetric flask support accurate standard preparation.

• A candidate writes, “A calibration can be built from unknown concentrations only.” Which correction should replace it?

Guided evidence check

The selected wavelength should give analyte response and minimise overlap from other species.

A cuvette should be oriented consistently and kept clean of fingerprints and bubbles.

• Which labelled diagram, spectrum or calculation would most directly disprove “An unknown far outside the standard range should be read by unlimited extrapolation.”?

Start the diagnostic and follow its feedback

Independent transfer

An anomalous standard should be investigated rather than silently forcing the line through it.

A report states calibration equation, measured absorbance, diluted result, dilution correction and final units.

• Design a specific chemical check that would expose the error in “Dilution before measurement does not affect the reported original concentration.”

Misconception repair

Misconception: Every anomalous standard should be retained without investigation.

Repair: An anomalous standard should be investigated rather than silently forcing the line through it.

• Write leaf-specific feedback for the misconception “Every anomalous standard should be retained without investigation.”

Practice, unseen assessment, re-test and next step

Complete the diagnostic questions, review the feedback, then attempt the final check.

After delayed re-test, continue to Distinguish atomic and molecular orbitals at /learning/h3-molecular-orbitals-atomic-and-molecular-lesson.html.

• Review the feedback for each diagnostic question, then attempt the final check.