Releasing Dinosaur Breath
In this activity, carbon dioxide is released from chalk (calcium carbonate) by reacting it with vinegar (a weak acid). Millions of years ago the carbon (from atmospheric carbon dioxide) was used by the fossil marine organisms that make their hard parts such as the shells of shelly organisms and the discs of calcareous algae. Limestone, including natural chalk, is made of the remains of these marine organisms that lived and died millions of years ago When limestone and chalk are formed carbon is locked away as calcium carbonate for millions of years (until we came along and poured acid onto them!). This is part of the Earth’s carbon cycle.
• Eye protection
• Crushed natural chalk
• Vinegar (alternatively use dilute hydrochloric acid (1 mol dm-3), which has the advantage of not smelling)
• Limewater (calcium hydroxide solution)
• Pour limewater into the test tube to a depth of 2 cm
• Place the crushed chalk in the flask.
• Add vinegar (or hydrochloric acid) to the flask and quickly place the balloon over the flask neck making sure there are no gaps.
• When the reaction has stopped (when the fizzing stops) pinch the balloon tightly at the neck so no gas can escape and remove it from the flask.
• Move the balloon over to the test tube and squeeze the balloon so the gas goes into it.
• Observe the limewater.
• What color was the limewater to begin with? = Colorless.
• What happened to the limewater when you added the gas from the balloon? It became cloudy.
• Where did the gas in the balloon come from? The chalk.
• What reaction was responsible for creating it? The reaction of calcium carbonate with acid.
• What gas was released from the chalk by the reaction? Carbon dioxide.
• Where did the dinosaurs get their carbon from? Eating plants and/or animals
• Why could you say that “dinosaur breath” was released from the chalk? How did it get there? Chalk is made of the hard parts of millions of tiny organisms. They used carbon, to make their hard parts (calcium carbonate) which they obtained from the sea water in which they lived in the form of dissolved carbon dioxide (many of these tiny organisms were photosynthesisers). The carbon dioxide in the ocean got there via gas exchange with the atmosphere. Carbon dioxide in the atmosphere, in turn, got there from animals (including dinosaurs) exhaling. So, the carbon dioxide is released from chalk might have been breathed out by a dinosaur (although, of course the carbon has been through many stages and has been combined in a range of other molecules in between times).
• Draw a dinosaur on the geological carbon cycle diagram and draw arrows to show the steps from how the dinosaurs got carbon to how carbon dioxide from the dinosaur got into the chalk