Question

a student was asked to formulate a hypothesis about what would happen if 100. ml of 0.1 m naoh(aq) at 25°c was combined with 100. ml of 0.1 m mgcl₂(aq) at 25°c. which of the following hypotheses indicates that the student thought a chemical change would occur?
a the volume of the resulting solution will be equal to the sum of the volumes of the original solutions.
b the mass of the resulting solution will be equal to the sum of the masses of the original solutions.
c the resulting solution would contain a precipitate.
d the resulting solution will be clear.

Explanation:

Step1: Analyze the reaction

When \(NaOH\) and \(MgCl_{2}\) react, the chemical equation is \(2NaOH(aq)+MgCl_{2}(aq)=Mg(OH)_{2}(s)+2NaCl(aq)\). \(Mg(OH)_{2}\) is a sparingly - soluble base (precipitate).

Step2: Evaluate each option

• Option A: Volume change is a physical property. Just stating that the volume of the resulting solution is equal to the sum of the volumes of the original solutions does not indicate a chemical change.
• Option B: Mass conservation is a physical law (law of conservation of mass). Saying that the mass of the resulting solution is equal to the sum of the masses of the original solutions is a physical principle and does not imply a chemical change.
• Option C: The formation of a precipitate (\(Mg(OH)_{2}\) in this case) is a clear indication of a chemical change. A new substance (the precipitate) is formed as a result of a chemical reaction.
• Option D: A clear solution could be either a result of no reaction (if no precipitate or other visible change occurs) or a reaction where the products are soluble. But it does not strongly indicate a chemical change like the formation of a precipitate.

Answer:

C. The resulting solution would contain a precipitate.