What is the role of the filter paper in the method of making salt crystals?

The role of filter paper in the process of making salt crystals primarily involves separating undissolved substances from a solution. When creating salt crystals, a common method is to mix a soluble salt with water and then add an insoluble substance (like copper oxide) to react and form the salt. After allowing the reaction to occur, filtering the mixture through filter paper enables the removal of the undissolved copper oxide. The filter paper allows the liquid solution containing the dissolved salt to pass through while trapping the solid impurities. This step is crucial in obtaining a clear solution from which the crystals can later be formed through evaporation or cooling processes.