Earth and Environmental Science 11–12 · Year 11

Chemical weathering of limestone: reaction of calcium carbonate with dilute acid

Module 1: Earth’s Resources

Practical, model not builtMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Carbonate rock dissolves in acid at a rate set by surface area, concentration and temperature, the same chemistry that forms caves and soil from limestone.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

1 mol/L hydrochloric acid splashes
pressure build-up if the delivery tube is obstructed
hot water bath

Controls

safety glasses
stopper loosely and never seal without a gas outlet
small volumes
rinse spills with water

Note

Chemicals are used: follow the NSW Department of Education Chemical Safety in Schools (CSIS) package, Section 1 (general information for all staff, including the CSIS 1.7 risk assessment requirement), read the Safety Data Sheet for each chemical and complete a RiskAssess risk assessment before the lesson.

What you need

marble chips (calcium carbonate) in two size grades, in 0.30 g portions weighed to 0.01 g
1 mol/L hydrochloric acid, 25 mL per run (or white vinegar for a slower run)
conical flask with a side arm or bung and delivery tube, gas syringe 100 mL or inverted measuring cylinder over water
stopwatch, balance to 0.01 g, thermometer, water bath

How to do it

Put 0.30 g of large chips in the flask, add 25 mL of acid, stopper at once and record the gas volume every 15 s until it stops rising.
Repeat with 0.30 g of small chips at the same temperature, then with large chips and acid warmed 10 °C above room temperature in the water bath.
Plot gas volume against time for each run and read the initial rate from the gradient of the first 30 s.
Compare the final volume with the volume calculated from the mass of calcium carbonate.
Relate the surface-area result to the cracks and joints in a limestone outcrop and the temperature result to cave chemistry.

What you should see

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. 0.30 g of calcium carbonate is 0.00300 mol and gives 72.1 mL of carbon dioxide at 20 °C and 101.3 kPa (73.3 mL at 25 °C), so the 100 mL syringe holds the whole run; 25 mL of 1 mol/L acid (0.025 mol) is more than four times the 0.0060 mol needed, so the acid is in excess and the plateau marks the end of the carbonate. Some carbon dioxide dissolves in the solution, so the collected volume can fall a little short. Small chips give a steeper initial gradient than large chips and the warmer run is faster; if the activation energy is taken as 50 kJ/mol, an assumed value the model lets the learner change, the rate rises by a factor of 1.97 from 20 to 30 °C.

What changes

What you change: chip size (surface area) or temperature
What you measure: volume of carbon dioxide against time; initial rate in mL/s
What you keep the same: mass of calcium carbonate 0.30 g
acid volume and concentration
temperature when surface area is tested
same apparatus and reading interval

Common misconceptions

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

Weathering is only physical breaking.
A rock that fizzes is dissolving in water alone (it is the acid).

Curriculum references

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

Earth and Environmental Science Stage 6 Syllabus (2017), NESA; current, replaced by the 11–12 Syllabus (2025) from 2028EES11-8 EES11/12-3 EES11/12-4 EES11/12-5
Earth and Environmental Science 11–12 Syllabus (2025), NESA; to be implemented from 2028, not yet taughtEES-11-02
Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-9
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities