Ascientist compares two samples of white powder. one powder was present at the beginning of an experiment. the other powder was present at the end. she wants to determine whether a chemical reaction has occurred. she finds that neither sample bubbles or dissolves in water. she measures the mass and volume of the solids. sample one has a volume of 45 cm3 and a mass of 0.5 g. sample two has a volume of 65 cm3 and a mass of 1.3 g. what should the scientist conclude? a)the samples have the same color, so no chemical reaction has occurred. b)the two samples do not react with water, so no chemical reaction has occurred. c)the densities of the samples are different, so a chemical reaction has occurred. d)the densities of the samples are the same, so no chemical reaction has occurred. e)the densities of the samples are different, so no chemical reaction has occurred.

The particle in a two-dimensional well is a useful model for the motion of electrons around the indole ring (3), the conjugated cycle found in the side chain of tryptophan. we may regard indole as a rectangle with sides of length 280 pm and 450 pm, with 10 electrons in the conjugated p system. as in case study 9.1, we assume that in the ground state of the molecule each quantized level is occupied by two electrons. (a) calculate the energy of an electron in the highest occupied level. (b) calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels. 9.27 electrons around the porphine ring (4), the conjugated macrocycle that forms the structural basis of the heme group and the chlorophylls. we may treat the group as a circular ring of radius 440 pm, with 20 electrons in the conjugated system moving along the perimeter of the ring. as in exercise 9.26, assume that in the ground state of the molecule quantized each level is occupied by two electrons. (a) calculate the energy and angular momentum of an electron in the highest occupied level. (b) calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels.

The mini-refrigerator fire was most likely caused by what type of wiring?

You throw a small rock straight up from the edge of a highway bridge that crosses a river. the rock passes you on its way down, 7.00 s after it was thrown. what is the speed of the rock just before it reaches the water 28.0 m below the point where the rock left your hand? ignore air resistance.