An experiment is performed in which a crystalline substance is added to a beaker filled with room-temperature water. The following observations were made: 1. The crystals dissolve. 2. A precipitate forms. 3. The bottom of the breaker feels warm to the touch. 4. Bubbles begin to form in the water. Which observations are evidence that a chemical reaction took place?

Describe in detail the melting point behavior of the 80: 20 benzoic acid-mandelic acid mixture

Determine the percent sulfuric acid by mass of a 1.61 m aqueous solution of h2so4. %

Which statement best describes the relationship between period and frequency of light waves? a) in wave b the period increases and the frequency decreases from wave a. b) in wave a the period increases and the frequency decreases from wave b. c) in wave b the period is shorter and the frequency is greater than in wave a. d) in wave a the period is shorter and the frequency is greater than in wave b.