Uranium-235 (U-235) has a half-life of around 700 million years. U-235 will decay into (after a series of separate decays) Pb-206 (Lead-206). A rock sample is found to have 6.25% (1/16) of its original U-235. a.) How many half-lives have passed?

b.) How many years has this taken?

c.) If there were 30 grams of U-235 originally, how many grams would be left now?

What is the molality of a solution that has 4 mol of kci in 0.800 kg of water

Drag each label to the correct location on the chart. classify each reaction as endothermic or exothermic.

Tooth enamel consists mainly of the mineral calcium hydroxyapatite, ca_10(po_4)_6(oh)_2. trace elements in teeth of archaeological specimens provide anthropologist with clues about diet and diseases of ancient people. students at hamline university measured strontium in enamel from extracted wisdom teeth by atomic absorption spectroscopy. solutions with a constant total volume of 10.0 ml contained 0.726 mg of dissolved tooth enamel plus variable concentrations of added sr. added sr find the concentration of sr in the 10 ml sample solution in parts per billion = ng/ml. find the concentration of sr in tooth enamel in parts per million = mu g/g.