Two colourless solutions of soluble salts were mixed together and a bright yellow solid appeared at once in the mixture. No temperature change was noticed. ...
Question 1 Report
Two colourless solutions of soluble salts were mixed together and a bright yellow solid appeared at once in the mixture. No temperature change was noticed. Which term best describes both the type of change and the solid that formed?
Answer Details
Two clear solutions were mixed and a bright yellow solid appeared at once. That solid must have been made in the mixture, because neither starting solution contained a visible solid, so ions from one solution have combined with ions from the other to form an insoluble compound. An insoluble solid formed in this way is called a precipitate, and making a new substance means the change is chemical.
A physical change forming a crystal would require cooling or evaporation, not simple mixing, and would give the original solute back. Evaporation leaves a residue only after the water has been driven off, which has not happened here. Melting is ruled out because a solid appeared rather than disappeared.
No temperature change is not evidence against a reaction; a precipitation can be almost thermally neutral.
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