RockLicker · Grade 7 · Lesson 1 of 5

Density Is One Clue

Calculate density from supplied measurements and avoid treating a matching value as a unique ID.

  • Grade 7
  • 50 minutes
  • Worksheet + teacher guidance
Back to Grade 7

What you will learn

Density is mass divided by volume. A volume measured by water displacement is the change in level, not the final reading. Several materials can share similar densities.

Words to use

  • density: mass per unit volume
  • displacement: change in water volume
  • precision: detail of a measurement

Evidence for this lesson

Illustrative measurements: A—mass 27.0 g, cylinder 50.0 to 60.0 mL. B—mass 40.5 g, cylinder 50.0 to 65.0 mL. Assume no trapped air, dissolution or absorption for the calculation.

Use the supplied record as written; do not invent missing results.

Work through the activity

  1. 10 min · Find volumeSubtract initial from final cylinder readings for samples A and B. Recall that 1 mL of displaced volume equals 1 cubic centimeter.
  2. 15 min · CalculateDivide each mass by its displacement volume. Include units and keep rounding consistent with the supplied readings.
  3. 15 min · InterpretCompare the densities. Explain why different masses do not automatically mean different materials and why similar density does not prove identical composition.
  4. 10 min · Evaluate errorsDiscuss trapped air, water absorption and reading error as possible issues in real tests. Propose another independent property to compare.
RockLicker
GRADE 7 · LESSON 1

Density Is One Clue

Draw on the printed sheet or write, type or dictate your response.
Draw on the printed sheet or write, type or dictate your response.
Draw on the printed sheet or write, type or dictate your response.
Draw on the printed sheet or write, type or dictate your response.

Responses stay in this open page only. Print before closing or changing pages; no student record is stored online.

Check your understanding

For A, which volume belongs in the density calculation?

Teacher & family guide · answers and assessment

Grade 7 · Density Is One Clue

Learning goal: Calculate density from supplied measurements and avoid treating a matching value as a unique ID.

Expected responses

  1. A: 60−50 = 10 mL; B: 65−50 = 15 mL.
  2. A: 27/10 = 2.7 g/cm³; B: 40.5/15 = 2.7 g/cm³.
  3. No. Equal density alone does not uniquely determine composition.
  4. Trapped air, absorption or reading error can affect volume; luster, hardness or cleavage adds evidence.

Understanding check: 10 mL. The sample changes the water reading by 10 mL; the entire final volume is not its volume.

Watch for this misconception

Use displaced volume rather than the final cylinder reading; density is one property, not a unique name.

Assess the evidence

Look for the observations, calculation or explanation named in the learning goal. Accept accurate drawings and dictated responses. Use the expected responses to discuss reasoning; a correct guess without explanation is a starting point for another conversation.

Adapt and extend

Read prompts aloud, enlarge print or let a partner record the learner’s explanation. Recalculate A if volume were misread as 9 mL and explain the effect.