You have solid potassium hydroxide KOH(s) and distilled water. You want to prepare 100 ml of aqueous potassium hydroxide solution KOH(aq) with the concentration c=0.250 mol dm−3. What is the mass of solid potassium hydroxide you need for that?

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What layer of the atmosphere is directly above the troposphere?

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.)