State if a chemical change has occurred. Give a reason for answer. A student mixes 2 unknown solutions together & notices a cloudiness forming.
Solid purple iodine crytrals are heated slightly & a purple cloud of iodine gas is observed.
When nitric acid is poured onto limestone, bubbling is seen.
Two colourless solutions at room temperature are mixed. After a minute, the temperature of the mixture is 60 degrees Celsius.
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1st: A typical high school expt would be to mix two salt solutions. The cloudiness is a PRECIPITATE (a new compound) so this is a chemical change.
2nd: The iodine has SUBLIMED, it has turned from solid into a gas without being liquid first. If you cool the iodine gas it will RESUBLIME back into solid iodine. This is a PHYSICAL change where no new substance is formed.
3rd: The nitric acid is reacting with calcium carbonate to make calcium nitrate, carbon dioxide, and water. New substances are formed - a chemical change.
4th: You would need to know what is being mixed here. It is possible for heat to be made if a chemical or physical change has happened.
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