The average speed of helium at 25â°c is 1255 m/s. convert this speed to miles per hour (mph).

In the analysis of hair and fiber samples, which does a compound comparison microscope allow for that a conventional compound microscope does not? a. simultaneous observation b. polarization c. fluorescence d. higher magnification

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

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.)