Gas forming reactions are also exchange reactions. The best example I can think of for this type of reaction is what happens when you put a piece of chalk in a cup of vinegar. The chalk, which is mostly CaCO3 (calcium carbonate) and vinegar (acetic acid) forms calcium chloride and carbonic acid, which isn’t stable and quickly turns into water and carbon dioxide. A faster version of this experiment is what happens when you take an effervescent tablet, like alka seltzer, and stick it in water, because the tablet is actually a solid form of baking soda and vinegar put together. What happens when you mix baking soda and vinegar together?
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Lots of bubbles! Baking soda and vinegar is a gas forming exchange reaction.
There’s actually two reactions going – the first one is a double displacement where the vinegar reactions with the backing soda to make sodium acetate and carbonic acid, but the carbonic acid is unstable and breaks into carbon dioxide and water. The bubbles you see from this reaction are the carbon dioxide bubbles escaping., Since CO2 is heavier than air, it sits on the surface or overflows off the side of the container. If you add soap to this reaction, you’ll see the bubbles more clearly. If you warm up the vinegar first, the reaction will happen faster. The white sludge at the bottom os sodium acetate that’s left ver. Adults use this in making rubber tires, for curing headaches… that sort of thing.
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