Chemistry 11–12 · Year 11

Boyle's law and Charles's law with a sealed syringe, pressure sensor and water bath

Module 2: Introduction to Quantitative Chemistry

Practical, model not builtLow risk

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The idea

For a fixed amount of gas, pressure times volume is constant at fixed temperature, and volume is proportional to absolute temperature at fixed pressure; both are limits of PV = nRT.

What you need

60 mL plastic syringe with Luer cap (or a gas pressure sensor with syringe attachment and data logger)
Bathroom scale or a set of 1 kg masses and a retort stand (if no sensor), with the syringe barrel diameter measured by vernier calliper
Second 30 mL syringe sealed at 20 mL of air with a Luer cap, and a 1 L beaker water bath with thermometer, ice and a kettle
250 mL conical flask sealed with a one-hole bung and short tube to the pressure sensor (Gay-Lussac run)
Ruler, graph paper or spreadsheet

How to do it

Boyle: draw 40.0 mL of air into the syringe and cap it; record atmospheric pressure from the sensor or a weather report.
Press the plunger to 35, 30, 25 and 20 mL, recording pressure at each volume (or the force from the scale, converted to pressure using the piston area and added to atmospheric pressure); wait ten seconds at each step for the gas to return to room temperature.
Plot P against 1/V and P against V; find the gradient of the first plot and compare P x V across the readings.
Charles: place the 20 mL sealed syringe in iced water, then water at 20, 40, 60 and 80 degrees Celsius; wait two minutes at each temperature and read the volume with the plunger free to move.
Plot V against temperature in degrees Celsius, extend the straight line back to V = 0 and read the intercept; replot against kelvin.
Gay-Lussac: immerse the sealed flask in water at 0, 20, 40, 60 and 80 degrees Celsius, wait three minutes at each and record the pressure; plot P against T in kelvin and check that P/T is constant.
Run the simulation to check both plots against PV = nRT for the same amount of gas.

What you should see

Boyle: P x V stays close to the ideal 4052 kPa mL (40.0 mL at 101.3 kPa) at every step; halving the volume from 40.0 mL to 20.0 mL raises the pressure to 202.6 kPa, and P against 1/V is a straight line through the origin. Charles: 20.0 mL at 20 degrees Celsius grows to 22.7 mL at 60 degrees Celsius; the V against temperature line extrapolates to zero volume near minus 273 degrees Celsius, the exact intercept depending on the short temperature range and syringe friction. Gay-Lussac: air sealed at 101.3 kPa and 20 degrees Celsius reads 115.1 kPa at 60 degrees Celsius, and P against T in kelvin is a straight line through the origin.

What changes

What you change: volume (Boyle) or water-bath temperature (Charles, Gay-Lussac)
What you measure: pressure (kPa) or gas volume (mL)
What you keep the same: amount of trapped gas
temperature during the Boyle run
pressure (plunger free) during the Charles run
volume (sealed flask) during the Gay-Lussac run
settling time before each reading

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Doubling the temperature in degrees Celsius doubles the volume (only the kelvin temperature is proportional to volume).
Compressing a gas heats it permanently (it warms briefly and then returns to room temperature; that is why readings wait ten seconds).
Gas pressure comes from particles pushing each other (it comes from collisions with the walls).

Safety card

Low riskLearners carry it out

Hazards

hot water bath at 80 degrees Celsius
a capped syringe forced hard can pop its cap

Controls

do not compress below one third of the starting volume
tongs for the hot syringe
eye protection

Note

NSW Department of Education Chemical Safety in Schools (CSIS) package, 2021 Technical Update: Section 1.7 (risk assessment) and Volume 2 Appendix D (generic assessment advice and DoE chemical categories); record a RiskAssess (riskassess.com.au) risk assessment before the lesson and check the school's hazardous chemical register (CSIS Section 1.9) for local restrictions.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH11-9 CH11/12-2 CH11/12-4 CH11/12-6
Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-11-02 CH-11WS-02 CH-11WS-06
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities