Chemistry · Year 11

Active learning ideas

Concentration: Percent by Mass/Volume

Active learning works for percent by mass and volume because students often confuse the two concepts without hands-on practice. Measuring and calculating concentrations themselves helps them distinguish when to use mass versus volume units, turning abstract formulas into concrete understanding.

• ACARA Content Descriptions
• ACSCH064
• ACSCH065

• 25–50 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Collaborative Problem-Solving
• 50 min · Pairs

Lab Pairs: Prepare and Calculate Concentrations

Pairs select a solute: salt for 5% mass or food coloring for 10% volume. Measure solute and solvent accurately, prepare 100 mL solutions, stir to dissolve, then recalculate actual concentrations using final measurements. Record and compare with partner.

Differentiate between percent by mass and percent by volume concentration units.

Facilitation Tip

During Lab Pairs: Prepare and Calculate Concentrations, circulate to ensure students weigh liquids and solids directly rather than measuring by volume when preparing percent by mass solutions.

What to look for

Provide students with a scenario: 'A 500 mL bottle of rubbing alcohol contains 350 mL of pure alcohol.' Ask them to calculate the percent by volume concentration and explain why this unit is appropriate for this liquid-liquid solution.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 02

• Collaborative Problem-Solving
• 40 min · Small Groups

Station Circuit: Unit Selection Scenarios

Set up four stations with scenarios: pharmacy IV drip, soft drink mix, paint thinner, fertilizer spray. Small groups choose mass or volume percent, justify, and solve calculations at each station before rotating. Debrief as class.

Construct calculations to determine the percent concentration of a solution.

Facilitation Tip

At Station Circuit: Unit Selection Scenarios, provide unlabeled containers of solutions so students must decide whether to use mass or volume units before calculating.

What to look for

Give students two cards. On one card, they write a problem calculating percent by mass for a solid solute. On the second card, they write a problem calculating percent by volume for a liquid solute. They must also write the answer to each problem.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 03

• Collaborative Problem-Solving
• 30 min · Individual

Data Analysis: Dilution Challenges

Provide pre-made solutions with measured data. Individuals calculate initial and diluted concentrations using both units, then pairs discuss which unit best tracks changes. Share findings whole class.

Analyze situations where different concentration units are more appropriate.

Facilitation Tip

In Data Analysis: Dilution Challenges, give students volumetric flasks and graduated cylinders to demonstrate how total volume changes upon mixing, reinforcing the need for post-mixing measurement.

What to look for

Pose the question: 'Imagine you are making a saline solution for medical use. Would you use percent by mass or percent by volume? Justify your choice, considering the phases of salt and water.'

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 04

• Collaborative Problem-Solving
• 25 min · Pairs

Label Decoding: Consumer Products

Pairs examine labels from household items like mouthwash or bleach. Extract volumes or masses, compute concentrations, and predict effects of dilution. Present one insight to class.

Differentiate between percent by mass and percent by volume concentration units.

What to look for

Provide students with a scenario: 'A 500 mL bottle of rubbing alcohol contains 350 mL of pure alcohol.' Ask them to calculate the percent by volume concentration and explain why this unit is appropriate for this liquid-liquid solution.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

A few notes on teaching this unit

Teach this topic by starting with simple, relatable examples like saline solutions or household cleaners. Avoid rushing to formulas; instead, let students derive the percent equations from their own measurements. Emphasize that units matter because solutions behave differently depending on whether the solute is solid or liquid. Research shows students grasp concentration best when they connect calculations to real-world contexts like medicine or food science.

Students will prepare solutions accurately, calculate concentrations correctly, and justify their unit choices with evidence. They will also recognize why percent by mass and volume produce different values and explain the role of density in these differences.

---

Watch Out for These Misconceptions

• During Lab Pairs: Prepare and Calculate Concentrations, watch for students measuring liquid solutes by volume when calculating percent by mass.

  Have students measure the mass of the solute directly on a balance and calculate the mass of the solvent by difference, then discuss why volumes are unreliable for mass-based calculations.

• During Station Circuit: Unit Selection Scenarios, watch for students choosing percent by volume for solid solutes like sugar in tea.

  Ask students to weigh the sugar before dissolving and measure the total mass of the solution to reinforce that percent by mass is the correct unit for solids.

• During Data Analysis: Dilution Challenges, watch for students assuming volumes are additive when mixing liquids.

  Have students measure the total volume after mixing to show contraction or expansion, then recalculate percent by volume using the actual final volume.

---

Methods used in this brief

• Collaborative Problem-Solving