← Young Researchers ScienceRate of reaction40 minutesStd 9–12

How Fast Does It Fizz

✨ The kitchen scale reading falls in real time, and the steepness of that fall is the speed of the reaction.

A glass of vinegar and baking soda on a kitchen scale losing carbon dioxide, beside a graph of mass lost in grams against time in seconds with four curves for full, three quarter, half and quarter strength vinegar, the strongest having the steepest start. — How it works

🧰 You need

baking soda
white vinegar and water for dilution
a kitchen scale reading to 1 gram
a tall glass or jar
a measuring cup and spoon
a phone timer

⚠️ Keep vinegar away from your eyes, wipe spills at once and keep the scale dry.

👀 What you will see

The mass falls fastest in the first few seconds and then levels off. Stronger vinegar gives a steeper start and reaches its final mass loss sooner. All four runs with the same 2 grams of baking soda end at a similar total loss, provided enough acid was present.

🧪 Do it

Make four vinegar solutions of 50 millilitres each: full strength, three quarters, half and one quarter, topping up with water.
Weigh 2 grams of baking soda for every run so that this variable stays fixed.
Stand the glass of one solution on the scale, note the total mass, then tip in the baking soda and start the timer.
Read the mass every fifteen seconds for two minutes and write every reading down.
Repeat for the other three concentrations, using the same glass, room and volumes.
Plot mass lost against time for all four runs on one set of axes.
Measure the gradient of each curve over the first thirty seconds and compare the four initial rates.

💡 Why it happens

Acetic acid in the vinegar reacts with sodium hydrogen carbonate to produce carbon dioxide, which escapes into the room, so the falling mass measures how much gas has been made. Rate of reaction is the change in that mass divided by the time taken, which is the gradient of your graph. A more concentrated acid has more acid particles in each cubic centimetre, so there are more successful collisions per second and a steeper initial gradient. The final mass loss is set by whichever reactant runs out first, called the limiting reactant, which is why runs with enough acid all end in the same place.

🔁 Now try this

Repeat the half-strength run with cold fridge vinegar and with room-temperature vinegar, and compare the two initial rates.

🤔 Think about it

Why does the mass stop falling even though there is still liquid acid in the glass?

🧘 Ask the Acharya

“Why does the mass stop falling even though there is still liquid acid in the glass?” — ask him and he will explain it from your own chapters.

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