Question

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what are three observations that would indicate a chemical reaction has taken place?

1. a change
2. the formation of an insoluble
3. the production of a

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Explanation:

• Color change: Many chemical reactions involve a visible change in color. For example, when iron rusts (reacts with oxygen and water), it changes from a shiny metallic color to a reddish - brown color.
• Formation of an insoluble precipitate: When two aqueous solutions react, if one of the products is insoluble in water, it will form a precipitate. For instance, when silver nitrate ($\ce{AgNO3}$) reacts with sodium chloride ($\ce{NaCl}$) in water, silver chloride ($\ce{AgCl}$) precipitate is formed ($\ce{AgNO3(aq)+NaCl(aq)\to AgCl(s) + NaNO3(aq)}$).
• Production of a gas: Some reactions produce a gas as a product. For example, when baking soda ($\ce{NaHCO3}$) reacts with vinegar (acetic acid, $\ce{CH3COOH}$), carbon dioxide ($\ce{CO2}$) gas is produced ($\ce{NaHCO3 + CH3COOH\to CH3COONa + H2O+CO2(g)}$).

Answer:

1. Color
2. Precipitate
3. Gas