1. radioactive decay of 40k atoms in an igneous rock has resulted in a ratio of 25 percent 40k atoms to 75 percent 40ar and 40ca atoms. how many years old is this rock?

Two things that biomedical has invented or innovated

An empty fuel tank can still contain and therefore can be even more dangerous than one full of liquid fuel.

Modern pennies are composed of zinc coated with copper. a student determines the mass of a penny to be 2.482 g and then makes several scratches in the copper coaling (to expose the underlying zinc). the student puts the scratched penny in hydrochloric acid, where the following reaction occurs between the zinc and the hcl (the copper remains undissolved): zn(s) + 2 hcl(aq) → h2(g) + zncl(aq)the student collects the hydrogen produced over water at 25 °c. the collected gas occupies a volume of 0.899 l at a total pressure of 79 j mmhg. calculate the percent zinc (by mass) in the penny. (assume that all the zn in the penny dissolves.)