FCAT Grade 8 Science Assessment Practice Questions

Category - FCAT Science Assessment Grade 8

Alexi is performing a chemical reaction in a solution of water, seen below:
MgCl2(aq) + PbSO4(aq) <-> MgSO4(aq) + PbCl2(s)
Alexi finds that PbCl2, lead chloride, is not soluble in water, and that the equation above is written incorrectly. Why is the equation not correct?
  1. The reaction is not reversible.
  2. One of the products should be Mg2SO4.
  3. Lead chloride should be aqueous in solution.
  4. Magnesium chloride and lead sulfate are both solids.
  5. The equation is actually correct.
Explanation
Answer: A - The reaction is not reversible, because lead chloride is not soluble in water. Reactions must occur in the same phase, and generally only occur in the aqueous or gas phases. There is a small amount of reaction that can occur between the aqueous and solid phases, but it progresses extremely slowly!
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