Photo AI
Substance X reacts with water - CIE - A-Level Chemistry - Question 14 - 2019 - Paper 1
Question 14
Substance X reacts with water. A gas is given off and the pH of the solution increases. The solution is then reacted with sulfuric acid and a white precipitate forms... show full transcript
Worked Solution & Example Answer:Substance X reacts with water - CIE - A-Level Chemistry - Question 14 - 2019 - Paper 1
Step 1
What could be substance X?
Answer
To determine what substance X could be, we need to analyze the reactions described in the question.
-
Reaction with Water: The information states that substance X reacts with water to produce a gas and that the pH of the solution increases. This suggests that a metal or metal oxide that produces hydrogen gas (H₂) is likely involved. Metals such as barium and magnesium can react with water to release hydrogen gas, while metal oxides generally do not.
-
Gas Evolution and pH Increase: A significant increase in pH indicates the formation of a strong base, which would be expected if a metal reacts with water. Barium, when reacting with water, produces barium hydroxide (Ba(OH)₂), a strong base that increases the pH significantly. Magnesium reacts with water but does so at a slower rate and primarily in the presence of heat.
-
Reaction with Sulfuric Acid: The question also mentions that after the reaction with water, substance X is reacted with sulfuric acid, and a white precipitate forms. This suggests that the substance might yield a compound that is typically insoluble with sulfuric acid. For instance, barium ions (Ba²⁺) react with sulfate (from sulfuric acid) to form barium sulfate (BaSO₄), which is a white precipitate.
-
Conclusion: Given that barium not only reacts with water to produce hydrogen gas and hydroxide ions, thus increasing the pH, but also forms a white precipitate when reacted with sulfuric acid, the most likely candidate for substance X is A. barium.