Infer particle attractions from bulk properties

What can a controlled evaporation investigation suggest about particle attractions?

Submit: An evidence record, explanation and revision.

Related lesson: Chemical Bonding

This is a teacher-led extension beyond the short lesson. The task supplies a performance opportunity; completion alone does not certify mastery, full NGSS coverage or state alignment.

Build the idea

Bulk properties depend on interactions among particles as well as particle structure and mass. Electrical attractions among charged parts of molecules help explain why liquids hold together. Evaporation requires some particles to overcome attractions. One evaporation comparison alone cannot uniquely identify every force or establish a universal ranking.

Evidence and model inputs

Investigation uses water and teacher-approved 70% isopropyl rubbing alcohol on separate identical inert surfaces. The alcohol product is a mixture, so its behavior is not a pure-substance constant. No example results are supplied. The teacher may instead supply measured mass-loss records from this exact protocol with product concentration, timing and room conditions documented.

Keep actual observations, published findings and invented model cases labeled separately. If a source or required equipment is unavailable, pause that part with a teacher; do not invent results.

Materials and preparation

Teacher-managed approved liquids, goggles, ventilation, identical inert surfaces, timer or suitable balance; no flames or hot equipment.

Grade-level scope

No hazardous heating or student solvent handling without teacher approval. Do not infer exact force strengths from a single bulk property.

Do the work

1. Teacher assesses ventilation, fire risk and school chemical rules; use only a few drops, goggles, no heat or ignition sources and no skin application. A teacher conducts dispensing.
2. Plan equal starting volumes, equal exposed areas, matching surfaces and simultaneous timing. Record room conditions and repeat three paired trials.
3. Measure evaporation time or mass change with a suitable balance. Record uncertainty and avoid mixing the liquids.
4. Use a particle model to connect observed bulk differences with electrical attractions while accounting for composition and molecular differences.
5. Propose a second bulk property, such as published boiling-point data for pure substances, that would strengthen or challenge the inference.

Learner worksheet

Write on paper or type here and print. Entries stay in this page’s memory and are lost when you leave or reload; they are not saved or submitted.

Check your reasoning

1. Does faster evaporation prove there are no attractions?
2. Why record concentration?
3. Can different drop areas confound the comparison?
4. What conclusion is defensible?

Teacher review guide

Review the actual deliverable and discuss the reasoning. For each criterion, use 0 when evidence is absent or fundamentally incorrect, 1 when partly supported with a material error or omission, and 2 when accurate, supported and complete for the stated task. Maximum 8 points is a task score, not a proficiency certification. Give feedback and allow revision.

1. Plans and conducts a controlled bulk-property investigation.
2. Records repeated measurements and relevant uncertainty.
3. Connects observations to electrical interactions among particles.
4. Evaluates composition and alternative explanations.

Sources and standard reference

• Official NGSS HS-PS1-3 performance expectation — inspect the practice, core idea, crosscutting concept and assessment boundary.

Instructional text and hypothetical cases are original. Linked source readings supply published evidence where specified. Teachers should judge fit with their course and state requirements.