Can atoms change identity during a chemical reaction

Esign techniques and materials that reduce the negative environmental impact of a structure are referred to as

Sodium sulfate dissolves as follows: na2so4(s) → 2na+(aq) + so42- (aq). how many moles of na2so4 are required to make 1.0 l of solution in which the na concentration is 0.10 m?

Air can be considered a mixture. which statement does not explain why?