You have a 10.0 g sample of gallium-68. Half of it decays in 68.3 minutes. How much will be left after two half-lives? Make sure to round to the correct number of significant figures and use units (g)

You are attempting to recrystallize a crude product mixture. you add the appropriate amount of hot solvent and are allowing the solution to slowly cool to room temperature. however, at room temperature no crystals have appeared, which of the following methods should be used to induce crystallization? choose all correct answers. a) place the flask in an ice bath. b) swirl the contents of the flask. c) add a small seed crystal of the desired product. d) scratch the inside of the glassware using a stir rod. it can be multiple choices

Which elements are found in glucose, the product of photosynthesis? a. carbon, hydrogen, and oxygen b. carbon and hydrogen c. carbon, nitrogen, and oxygen d. hydrogen, nitrogen, and carbon

Which change will decrease the number of effective collisions during a chemical reaction? a. adding a catalyst b. increasing the surface area c. decreasing the temperature d. increasing the reactant concentrations e. increasing the volume of the reactants