STEM MODEL AND EVIDENCE WORKBENCH
Calculate two-isotope weighted means and audit abundance totals and reported average-mass claims with visible contributions.
Review output
Load the worked example to inspect realistic inputs, or enter anonymous classroom or laboratory evidence. Results remain in this browser tab until you copy or download them.
Transparent method
Weighted mean equals mass A times abundance A divided by one hundred plus mass B times abundance B divided by one hundred. Abundances must total 100 percent within 0.05 percentage points. Claim agreement uses an absolute 0.01 u tolerance after calculation at full precision. A supported row has a complete abundance total and a reported value close to the weighted mean. The average should lie between included isotope masses and nearer the more abundant isotope. An invalid total means the composition must be corrected or completed before the average can represent the sample.
Confirm the task, approved source, units, notation, signs, model assumptions, and review threshold. Keep an unchanged copy of measurements or learner responses.
Run the worked example, inspect every intermediate row, and compare the result with a hand calculation, diagram, physical model, periodic table, or approved laboratory method.
Record the method, assumptions, uncertainty, units, classifications, and flagged rows. Verify the editable report independently before instruction, assessment, or laboratory use.
How to interpret the result
Use for a bounded two-isotope weighted-average exercise or data review. It does not handle a third isotope, solve an unknown abundance, identify a sample, distinguish natural from enriched material, model instrument peaks, or propagate mass-spectrometry uncertainty. Real elements require all relevant isotope evidence.
The chlorine and copper rows reproduce familiar weighted averages within 0.01 u. An equal fictional mixture produces exactly 11.0 u. The final row has abundances totaling only ninety percent; even though a number can be calculated, the claim is not supported because ten percent of the composition is missing.
Weighted mean equals mass A times abundance A divided by one hundred plus mass B times abundance B divided by one hundred. Abundances must total 100 percent within 0.05 percentage points. Claim agreement uses an absolute 0.01 u tolerance after calculation at full precision.
A supported row has a complete abundance total and a reported value close to the weighted mean. The average should lie between included isotope masses and nearer the more abundant isotope. An invalid total means the composition must be corrected or completed before the average can represent the sample.
Do not average isotope masses without weights, use mass numbers in place of measured isotopic masses, enter percentages as whole multipliers, round each contribution early, or force an incomplete total to one hundred without evidence. Record the source, sample basis, precision, and all relevant isotopes.
Learning boundary
This browser-local workbench applies only the disclosed rules. It cannot diagnose learning, certify an experiment, identify a substance, establish a structure, or replace teacher, laboratory, and safety judgment.
Review checklist
Practical questions
No. Processing occurs in the current browser tab. Avoid personal information and retain authoritative records only in the school-approved system.
No. It describes entered evidence under one disclosed rule. Compare several evidence sources and ask for reasoning before drawing a conclusion.
Treat it as an editable calculation aid. Show your own reasoning, cite required sources, and follow the course method and academic-integrity rules.
YOUR NIRMION
