Acids, alkalis and the pH scale：練習問題

When preparing the soluble salt ammonium sulfate from aqueous ammonia and dilute sulfuric acid, why is a titration method used rather than adding one reactant in excess?

A student electrolyses aqueous sodium chloride using inert graphite electrodes.
Which of the following explains why hydroxide ions, \(OH^-\), remain in the solution around the cathode, and what is the effect on the pH in that region?

In the electrolysis of aqueous copper(II) chloride using graphite electrodes, the following observations are made:
- A brown solid forms at the cathode.
- A pale green gas forms at the anode.
Which statement correctly identifies the redox process and the half-equation occurring at the anode?

A student wants to prepare a pure, dry sample of the insoluble salt barium sulfate. They have access to the following four chemicals:
1. Barium carbonate (solid)
2. Barium nitrate (solution)
3. Sodium sulfate (solution)
4. Sulfuric acid (dilute)

Which combination and method would reliably produce the highest purity sample of the salt?

A solution has a pH of 3. If the concentration of hydrogen ions, \([H^+]\), is decreased by a factor of 1000, what is the new pH of the solution and how is it classified?

When potassium is added to water, a violent reaction occurs. Write the balanced chemical equation, including state symbols, for this reaction and state the test used to identify the gas produced.

During the electrolysis of aqueous sodium chloride using inert electrodes, chlorine gas is produced at the anode.
Explain why hydrogen gas, rather than sodium metal, is produced at the cathode, and provide the ionic half-equation for the formation of hydrogen.

A sample of copper metal is purified using electrolysis.
Write the balanced half equation for the reaction occurring at the cathode during this process and state whether this is an oxidation or reduction reaction.