How much gas comes off a marble chip?
Marble chips and acid fizz. That is a fact, and the confirmatory test proves the gas is carbon dioxide. Neither says HOW MUCH — and how much is the question a Class 11 paper actually asks. This activity runs the same reaction on the quantitative bench, where every reagent goes in at a stated strength and the notebook shows the working: moles in, the ratio applied, which reagent runs out first, and the volume of gas that follows from it. Then it asks you for those numbers before it shows you the answer.
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8 steps · Mole Concept · Stoichiometry · Acids, Bases & Salts · Chemical Reactions
What you will use
Apparatus
- Reaction beaker
- Lime water
Chemicals
- Marble Chips
- Dilute Hydrochloric Acid
- Limewater
The steps
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Drop three marble chips into the reaction beaker.
Three chips, half a gram each. The bench weighs them so you can count them.
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Pour in dilute hydrochloric acid, and choose 1 M when it asks.
Brisk effervescence, and a line of working under the step. Read it before you go on.
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How many millimoles of hydrochloric acid went in?
Volume in litres times the strength in moles per litre. Ten millilitres of 1 M.
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Which reagent ran out first? Give its formula.
Not the one there is least of — the one with the smallest amount ONCE the equation's ratio is applied. Two HCl are needed per CaCO3.
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What volume of carbon dioxide does that make, in millilitres at RTP?
Moles of gas times 24 litres per mole. The limiting reagent decides it; the chips left over change nothing.
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Pour lime water into the test tube.
Saturated, at 0.02 M — all that will dissolve. The bench does not offer you a choice here, because chemistry does not.
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Right-click the beaker and run a delivery tube into the lime water.
The gas you just counted now has somewhere to go — and it arrives carrying that number with it.
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Watch the lime water, and read its working.
Milky — and the working under it starts from the moles of gas computed next door, not from a fresh guess. The same carbon dioxide, counted once and used twice.
What it shows
The acid ran out first, and everything downstream followed from that one fact: the volume of gas, the chips left sitting in the beaker, and how much calcium carbonate clouded the lime water. A limiting reagent is not an extra step at the end of a calculation — it is the thing the calculation is about.