International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

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Which test is used to confirm the presence of water?

  1. Add anhydrous copper(II) sulfate and observe a color change

  2. Heat the solution and observe boiling

  3. Add sodium hydroxide and observe a pH change

  4. Expose to air and observe condensation

The correct answer is: Add anhydrous copper(II) sulfate and observe a color change

The presence of water can be confirmed using anhydrous copper(II) sulfate, which is a common laboratory reagent. In its anhydrous form, copper(II) sulfate is a white solid. When water is added, it reacts with the anhydrous copper(II) sulfate to form hydrated copper(II) sulfate, which changes the color from white to blue. This notable color change is a clear and simple visual indication that water is present. Other tests mentioned, such as heating a solution to observe boiling, do not specifically confirm the presence of water, as various substances can boil. Adding sodium hydroxide might indicate a pH change, but it does not specifically test for water. Lastly, exposing a substance to air and observing condensation might suggest the presence of moisture but is not a direct test for water itself. Thus, using anhydrous copper(II) sulfate is the most effective method for accurately confirming the presence of water.

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