Acid Attack
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
A piece of chalk. A cup of vinegar. Normal rain has a pH of around 5.6. Some rainwater measured in industrial areas tests at pH 3 — the same as vinegar. Watch what happens over 24 hours.
5-12 yrs
Easy
20
min
Stage 2, Stage 3
>
Acid Attack
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NESA Accredited Teacher
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High school chemistry & physics specialist 30+ years
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The Crazy Scientist in primary schools — 15 years
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International conference presenter on science education
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Creator of the LAB™ Learning System
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Curriculum aligned: NSW Science & Technology K–6 (2024)
A picture is worth a thousand words — check this out and see if you can spot the science hiding in plain sight.
What you will need
• 3–4 pieces of chalk — all roughly the same size
• White vinegar
• Water
• Small cups or containers — one per test sample
• Kitchen scales
• A ruler
• A notebook for recording
• Optional: pH paper or strips x
Who’s Leading This Mission?
Let’s Investigate
1
Weigh & Measure
Weigh each piece of chalk on the kitchen scales and record the mass in grams. Also measure the length with a ruler.
This is your starting data — you will compare it to measurements taken after 24 hours to calculate how much material was lost.
3
Observe 1
After one hour, look at both cups without disturbing them.
Record: is there any visible change to the surface of either piece of chalk? Any bubbles? Any sediment at the bottom? Any change in the liquid's colour or clarity?
5
Test real rain water
If you can collect rainwater in a clean cup, test its pH using pH paper and compare it to vinegar and tap water. Is your local rainwater acidic?
Where on the pH scale does it sit — and is it close to vinegar, or much milder?
2
Set up the tests
Place one piece of chalk in vinegar and another in plain water. Label each cup. If you have extra chalk, set up a control with no liquid at all.
Observe the chalk in vinegar immediately — what do you notice on the surface? Record your observations at time zero.
4
Observe 2
After 24 hours, carefully remove the chalk pieces and place them on paper towels to dry slightly.
Weigh and measure them again.
Calculate the mass lost (first reading take away second reading) and length lost for each. Compare vinegar vs water results.
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The Grand Canyon was carved over millions of years by the Colorado River. Water alone did not do it — slightly acidic water reacted with the limestone rock, dissolving it particle by particle.
Most rocks are stable in neutral water. But add acid — even a tiny amount — and the chemistry changes. The molecules in the rock react with the acid and break apart, releasing gases and leaving the rock softer, pitted, and lighter.
Predict: if you left a piece of chalk in vinegar for 24 hours, how much mass do you think it would lose? Write a specific prediction in grams or as a percentage — then weigh it before and after to find out.
Compare the starting and final mass of the chalk in vinegar vs the chalk in water. Was the difference larger than you predicted?
Describe the surface of the chalk after 24 hours in vinegar. What happened to the texture — and what does the sediment at the bottom of the cup consist of?
You saw bubbles forming on the chalk the moment it went into the vinegar. What gas was being produced — and where did it come from? (Hint: chalk is calcium carbonate.)
Chemical weathering dissolves rock through acid reactions. It is responsible for cave formation, limestone karst landscapes, and the pitting of historical monuments. It also releases minerals from rock into soil and water — which can help plant growth but can also harm aquatic ecosystems.
Acid rain has a pH below 5. Normal rain is about 5.6. The difference seems tiny — but pH is a logarithmic scale: pH 4 is ten times more acidic than pH 5. What does this mean for the difference in weathering rate between normal rain and acid rain?
Snails, clams, oysters, and coral reefs are all made of calcium carbonate. As ocean CO₂ levels rise, the ocean becomes more acidic — a process called ocean acidification. Based on your chalk experiment, predict what is happening to these organisms' shells and structures.
"Want the full teacher guide? The Crazy Scientist Lab includes classroom delivery tips, how to manage the WOW moment, differentiation for Stage 2 & 3, — ready to teach tomorrow."
Think Like a Scientist
Scientists don't just do ONE experiment; they change one part of the experiment (independent variable) and then see how it affects another part of the experiment
(dependent variable)
Change ONE variable and test again.
Does the concentration of acid change the erosion rate — does a more dilute vinegar solution (half vinegar, half water) dissolve chalk at half the rate of full vinegar, or is the relationship non-linear?
Does the surface area of the chalk affect how fast it erodes — does crushed chalk dissolve faster than whole chalk of the same mass in the same volume of vinegar?
🧪 Try it! Change ONE thing and test again. What did you discover?
Want to go deeper? Tap a section below to explore. ▼
The Science Behind It
What's really happening?
Chalk and limestone are both made of a mineral called calcium carbonate. When calcium carbonate meets acid, a chemical reaction happens: the mineral reacts and starts to break apart.
You can see it happening — bubbles form on the surface the moment the chalk goes into the vinegar. Those bubbles are carbon dioxide gas being released as the chalk dissolves.
The acid isn't just washing the chalk; it's chemically changing it into completely different substances. Solid material is being lost.
That's a chemical reaction — not just dissolving like sugar in water, but a permanent change where new substances are created.
Why vinegar models acid rain?
Normal rain is already slightly acidic — as rain falls through the air, it picks up a little carbon dioxide which makes it mildly acidic. This is natural and has been happening since long before humans existed.
Acid rain is different. It forms when gases from burning coal and petrol dissolve in rain clouds. Those gases react with water in the clouds to form real acids, and when that acid rain falls on buildings, statues, and rock faces, the same calcium carbonate reaction you're watching in your cup starts happening to the stone.
Slowly. Over years. Until the surface is pitted and crumbling.
How much difference does pH make?
The pH scale measures how acidic something is — 7 is neutral (pure water), lower numbers are more acidic, higher numbers are more alkaline. Vinegar sits around pH 3. \
Normal rain is about pH 5.6. That might not sound like much of a difference, but the pH scale is not like a ruler — each step is ten times more acidic than the last.
So vinegar is not just a bit more acidic than normal rain; it is roughly 1,000 times more acidic. This is why your chalk changed dramatically in 24 hours, but real limestone buildings change over centuries.
The chemistry is identical — only the concentration of acid is different.
Real-world connection
The Taj Mahal in India is made of white marble. It stood for 350 years without significant damage. Then industrialisation brought acid rain to northern India — from factories burning coal nearby. The marble began pitting and turning yellow.
A monument that had survived three and a half centuries started dissolving.
The same chemical reaction you ran in a cup has been happening to one of the most famous buildings in the world, just 1,000 times more slowly.
Try next
• See the same calcium carbonate reaction in a much more dramatic explosion → [The Volcanic Eruption]
• Find out what acid does to the calcium inside an actual bone → [The Bone Bender]
Extension: G&T Years 5 & 6
What the pH scale actually means.
pH is a measure of how acidic or alkaline a substance is, running from 0 (extremely acidic) to 14 (extremely alkaline).
What makes pH scientifically interesting is that it's a logarithmic scale — each step of 1 represents a tenfold change in acidity, not an equal change. So pH 4 is not just a little more acidic than pH 5 — it is ten times more acidic. pH 3 is one hundred times more acidic than pH 5.
Normal rain has a pH of about 5.6. Heavy acid rain can reach pH 4.0 or lower. That difference of 1.6 pH units represents roughly 40 times more acid — which explains why acid rain causes more damage than natural rain dramatically, even though the numbers look similar on the scale.
Your local water authority publishes the pH of tap water (usually around 7.0–7.5). If acid rain in your area has a pH of 5.0, how many times more acidic is the rain than the tap water? Show your reasoning using the logarithmic rule. Now calculate: how much more acidic is pH 4.0 acid rain compared to pH 5.6 normal rain?
Chemical weathering vs physical weathering
Weathering is the process of rock being broken down at the Earth's surface.
Physical weathering breaks rock into smaller pieces without changing its chemical composition — like water freezing inside cracks and splitting rock apart, or waves grinding boulders into sand.
Chemical weathering is fundamentally different: the rock reacts chemically with water, acids, or oxygen and is transformed into new substances. The calcium carbonate in chalk reacts with acid to form calcium ions, water, and carbon dioxide.
The mineral is gone — not just broken into smaller pieces, but permanently changed into different compounds. This difference matters because chemically weathered rock cannot be reassembled — the reaction is irreversible.
The Grand Canyon was carved partly by the Colorado River, cutting through limestone rock over millions of years. Slightly acidic river water was the tool. Based on what you know about chemical weathering, describe what was happening at a chemical level as the canyon slowly formed. Is the same process still happening today?
Vocabulary
Calcium carbonate
The mineral that makes up chalk, limestone, and marble. It reacts with acid to form new substances and releases carbon dioxide gas as bubbles.
Acid
A substance with a pH below 7. Acids react with certain minerals and materials, breaking them down chemically. Vinegar and lemon juice are weak acids.
pH
A measure of how acidic or alkaline something is, on a scale from 0 (very acidic) to 14 (very alkaline). 7 is neutral. Each step represents ten times more or less acid.
Chemical reaction
A process where substances combine or break apart to form completely new substances. The chalk dissolving in vinegar is a chemical reaction — carbon dioxide gas is produced.
Carbon dioxide
A gas is produced when calcium carbonate reacts with acid. The bubbles on the chalk surface are carbon dioxide escaping as the chalk dissolves.
Chemical weathering
The breakdown of rock through chemical reactions with water, acids, or other substances — permanently changing the mineral into new compounds.
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TOMORROW?
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