Ortable hot packs are available for skiers and other people engaged in other outdoor activities in a cold climate. the air-permeable paper packet contains a mixture of powdered iron, sodium chloride, and other components, all moistened by a little water. the exothermic reaction that produces the heat is a very common one, the rusting of iron: 4fe(s) + 3o2(g) → 2fe2o3(s) when the outside plastic envelope is removed, o2 molecules penetrate the paper, causing the reaction to begin. a typical packet contains 250. g of iron to warm your hands or feet for up to 4 hours. calculate the amount of heat (in kj) associated with this reaction.

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.