TutorForAll

Science and Technology K–6 · Year 5

Acid rain on limestone: chalk dissolving in vinegar

Science understanding: Earth and space sciences

Practical, model not builtLow risk

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

Chemical weathering dissolves some rocks, and calcium carbonate in chalk or limestone reacting with a weak acid loses mass that a balance can track, with the fizz as carbon dioxide.

What you need

  • sticks of blackboard chalk made of calcium carbonate (check the label; some chalk is calcium sulfate and will not react) or small limestone chips
  • white vinegar labelled 4 percent acidity (40 g of acetic acid per litre), 50 mL per cup; a bottle labelled 5 percent holds 50 g per litre and lifts every computed limit by a quarter
  • 3 clear cups and 3 more with tap water as controls
  • kitchen balance reading to 0.1 g
  • timer, paper towel

How to do it

  1. Soak each chalk piece in tap water for 5 minutes, pat it dry and weigh it; chalk is porous, and pre-soaking means later mass changes are chalk lost, not liquid soaked up. Use a piece of about 5 g.
  2. Drop it into 50 mL of vinegar and start the timer. Watch the fizz with a hand lens.
  3. After 5, 10 and 20 minutes lift the chalk out, pat it dry, weigh it and return it.
  4. Run the same chalk mass in tap water as the control.
  5. Graph chalk mass against time for both cups.
  6. Leave the vinegar cup overnight and weigh the chalk in the morning; compare with the computed limit.

What you should see

The chalk fizzes at once and loses mass steadily; the pre-soaked chalk in water stays close to its starting mass. Fifty millilitres of 4 percent vinegar holds 0.0333 mol of acetic acid, enough to dissolve at most 0.0167 mol of calcium carbonate, 1.67 g, releasing 0.41 L of carbon dioxide at 25 degrees Celsius, so a 5 g stick loses about 1.7 g overnight and then stops because the acid is used up, and a fresh 50 mL restarts it. Read the label before comparing: 50 mL of a bottle labelled 5 percent holds 0.0416 mol and lifts the limit to 2.08 g and 0.51 L. Chalk that is calcium sulfate does not fizz, which is itself a test of what the rock is made of.

What changes

What you change
vinegar or water; time
What you measure
mass of chalk remaining
What you keep the same
  • chalk mass
  • liquid volume
  • temperature

Common misconceptions

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

  • Only strong acids react with rock.
  • The chalk melts.
  • The fizz is air that was inside the chalk.

Safety card

Low riskLearners carry it out

Hazards

  • vinegar splash in eyes

Controls

  • safety glasses
  • wipe spills
  • no drinking

Note

Household chemicals only. Risk assessment before the lesson using the NSW Department of Education Chemical Safety in Schools package (CSIS 1.7 Risk Assessment) or Primary RiskAssess.

Curriculum references

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

  • Science and Technology K-6 Syllabus (2017), current, taught until 2026; a Stage 2 outcome, because NSW teaches gradual weathering and erosion in Stage 2 ('investigate why the Earth's surface changes over time as a result of natural processes and human activity'), while the Stage 3 surface-change content under ST3-10ES-S covers sudden geological change and extreme weather events, its other content group being Earth's place in our solar system; code read from the syllabus document on 22 September 2026ST2-10ES-S
  • Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-6MW-SST3-1WS-S
  • Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-DAT-01
  • Australian Curriculum v9AC9S5U02AC9S5I03AC9S5I04

Sources

The pages the author read to write this activity.

  1. www.scootle.edu.au/ec/search?accContentId=AC9S5U02
  2. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
  3. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
  4. primaryconnections.org.au/teaching-sequences/year-5/wear-on-earth
  5. edu.rsc.org/primary/popping-good-chemistry/4020270.article

All Concept Studio activities