Question

select the correct answer.
two beakers are on a laboratory bench. one beaker contains 1.0 m hcl and the other contains tap water. what could an experimenter do to distinguish the acid solution from the tap water?
a. drop a piece of magnesium in each solution.
b. drop a piece of copper in each solution.
c. dip a piece of red litmus paper in each solution.
d. smell the two solutions.

Explanation:

• Option A: Magnesium reacts with \(HCl\) (\(Mg + 2HCl=MgCl_{2}+H_{2}\uparrow\)), producing bubbles of hydrogen gas. Magnesium does not react with tap - water (at room temperature, the reaction of \(Mg\) with water is very slow and negligible for the purpose of this quick test).
• Option B: Copper is less reactive than hydrogen (\(Cu\) is below \(H\) in the reactivity series), so it does not react with \(HCl\) or water.
• Option C: Red litmus paper turns blue in basic solutions. \(HCl\) is acidic (\(pH<7\)) and tap - water is neutral (\(pH = 7\) approximately). Red litmus paper will not change color in either solution (it changes color in basic conditions).
• Option D: Both \(HCl\) (dilute) and tap - water are (relatively) odorless. Smelling is not a safe or reliable method for distinguishing them in a laboratory (laboratory safety rules advise against smelling chemicals directly).

Answer:

A. Drop a piece of magnesium in each solution.