What should be done after heating sulfuric acid when making salt crystals?

After heating sulfuric acid, stirring in excess copper oxide is an important step in the process of making salt crystals. When sulfuric acid reacts with copper oxide, which is a base, a neutralization reaction occurs. This results in the formation of copper sulfate and water. By adding excess copper oxide, you ensure that all the sulfuric acid is reacted. This is crucial because it drives the reaction to completion and prevents excess acid from remaining in the solution, which could affect the purity of the resultant salt crystals.

Once the reaction has taken place and excess copper oxide is stirred in, the mixture can then be filtered to remove any undissolved copper oxide that hasn't reacted, leaving you with a solution of copper sulfate. This prepares the solution for further steps, such as evaporation, which will yield the desired salt crystals.

In contrast, other options would not be suitable in this specific step of the process. For instance, filtering out copper oxide is something that would occur after the neutralization reaction is complete, not just after heating the sulfuric acid. Adding water to the solution is not necessary at this stage, as you aim to concentrate the sulfuric acid before combining it with copper oxide. Allowing the mixture to cool completely could delay the reaction and is