Investigating Matter — Chapter Practice, Grade 11

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

Problem 1

A 42.0 g sample occupies 15.0 mL. Find density.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

2.8 g/mL

42.0/15.0 = 2.80.

Problem 2

Three readings are 2.01, 2.02, 2.01 g/mL but the reference is 2.50. Interpret them.
Answer and explanation

Precise, but inaccurate relative to the reference; investigate calibration or consistent method bias.

Response criteria

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

Problem 3

A 18.0 g sample occupies 6.00 mL. Find density.
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

3 g/mL

18.0/6.00=3.00.

Problem 4

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 5

Convert 0.0350 kg to grams and preserve significant figures. Show the reasoning, not just the conclusion.
Hints

Unit conversion and significant figures are different checks.

Answer and explanation

35.0 g; the exact conversion factor 1000 g/kg does not reduce the three significant figures.

Problem 6

Repeated volumes are 9.8, 9.9 and 9.8 mL, but a reference is 10.5 mL. Explain precision versus accuracy.
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

The readings agree closely, indicating precision; their offset from the reference suggests lower accuracy or systematic error.

Problem 7

Reported digits should reflect the measuring processReported digits should reflect the measuring process2.03.0Read between marksInclude one estimate2.40 cm × 1.2 cm = 2.88 cm² → 2.9 cm²The limiting measured input has two significant figures.
Original schematic ruler and independent area calculation. The marker illustrates interpolation rather than supplying the dimensions for that area problem.
Interpret the supplied visual. Why is the area reported as 2.9 cm² rather than 2.8800 cm²?
Answer and explanation

The 1.2 cm input has two significant figures. The additional displayed calculator digits are unsupported measurement precision.

An instrument’s resolution is the smallest change it can distinguish or display; an analog scale usually supports an estimated digit beyond its marked intervals. That does not make every last digit exact. In classroom significant-figure rules, a multiplication result follows the least precise measured factor in significant figures. Addition and subtraction instead follow decimal-place precision. Keep guard digits while calculating and round once at the end; extra calculator digits cannot improve the original measurement.

The 1.2 cm input has two significant figures. The additional displayed calculator digits are unsupported measurement precision.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the chemistry relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

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 9

Why does a coffee filter not remove dissolved sugar?
Answer and explanation

Dissolved molecules pass through its pores with the liquid; filtration removes larger particles.

Response criteria

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

Problem 10

Explain why boiling and electrolysis of water are different kinds of change.
Answer and explanation

Boiling changes phase without changing H₂O; electrolysis is a chemical decomposition into hydrogen and oxygen.

Response criteria

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

Problem 11

A mixture contains 5 g salt and 8 g sand. After complete physical separation, what total dry solid mass should be recovered in a closed no-loss model?
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

13 g

5+8=13; material is redistributed, not created.

Problem 12

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 13

Classify pure copper, distilled water and air as element, compound or mixture. Show the reasoning, not just the conclusion.
Hints

Filtering alone cannot normally remove dissolved salt ions.

Answer and explanation

Copper is an element, water a compound, and air a mixture of gases under ordinary conditions.

Problem 14

Why does a variable composition support calling a material a mixture?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Mixture proportions can vary without a single fixed chemical formula; a pure compound has defined composition.

Problem 15

Choose a separation step because a physical property differsChoose a separation step because a physical property differsSalt + sand mixtureWater dissolves the saltFilter: sand retainedEvaporate filtrate → saltFiltration separates phases, not dissolved ions from water.
Original conceptual sand/salt route; actual material quantities, apparatus and drying conditions require a specified procedure.
Interpret the supplied visual. Why does filtering salty water not normally produce salt-free water?
Answer and explanation

Dissolved ions travel with water through an ordinary filter. A different separation process must exploit volatility, membranes or other relevant properties.

A separation method uses a property difference without requiring a chemical identity change. Filtration retains particles larger than a filter’s effective pores but does not normally remove dissolved ions. Selective dissolution can move salt into water while sand remains as a solid phase. Evaporation recovers a nonvolatile solute, while distillation can also collect condensed solvent vapor. Evaluate solubility, volatility, particle size and stability before choosing a method; a sequence can need several complementary steps.

Dissolved ions travel with water through an ordinary filter. A different separation process must exploit volatility, membranes or other relevant properties.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the chemistry relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 16

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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