Investigating Matter — Problem set, Grade 11

Build the measurement, classification, and evidence skills used throughout chemistry.

Review the key ideas

Measurement, Units & Experimental Evidence

Units, precision, and a stated method make numerical evidence interpretable.

Classifying Matter & Separating Mixtures

Identify particle composition first, then choose separation methods using physical differences.

Problem 1

A reference mass is 50.0 g; the measurement is 49.0 g. Find percent error.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

2 %

|49−50|/50 ×100 = 2%.

Problem 2

Design a repeatable density measurement for a small waterproof object.
Answer and explanation

Measure mass on a calibrated balance; record initial and final water volumes, subtract for displaced volume, repeat, and note trapped-air or scale-reading uncertainty.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

Chapter review: An unknown has mass 37.5 g at volume 15.0 mL. Three repeat densities cluster near 2.50 g/mL, but the independently certified reference is 2.80 g/mL. Calculate density and explain the evidence limits.
Answer and explanation

Density is 37.5/15.0 = 2.50 g/mL. Repetition supports precision, but the difference from 2.80 suggests a method/reference comparison issue; check calibration, conditions and uncertainties rather than claim identity from one property.

Density is 37.5/15.0 = 2.50 g/mL. Repetition supports precision, but the difference from 2.80 suggests a method/reference comparison issue; check calibration, conditions and uncertainties rather than claim identity from one property.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

A drink label lists dissolved sugar and flavoring. Is the drink one compound?
Answer and explanation

No. Multiple substances occur in variable proportions; a uniform drink is a homogeneous mixture.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

A wet towel loses 30 g while drying. Explain conservation.
Answer and explanation

Water crosses the towel-system boundary into air; include that vapor to conserve the total mass.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Chapter review: A mixture contains 6.00 g salt and 4.00 g sand. You recover 5.10 g of dry salt-containing material. Calculate apparent salt recovery and explain why its purity remains uncertain.
Answer and explanation

Apparent recovery is 5.10/6.00 ×100 = 85.0%. The calculation treats the recovered mass as salt, but residual sand or other substances require a separate purity test. Distinguish mass loss from composition evidence.

Apparent recovery is 5.10/6.00 ×100 = 85.0%. The calculation treats the recovered mass as salt, but residual sand or other substances require a separate purity test. Distinguish mass loss from composition evidence.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.
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