Final answer:
The white substance from the electrolysis of saltwater is likely a mixture including sodium hydroxide, but also potentially containing other compounds. Pure sodium hydroxide is highly soluble and would not precipitate as white solids under normal circumstances unless the solution is highly concentrated or the water has been evaporated.
Step-by-step explanation:
The white substance you obtained from the electrolysis of saltwater (aqueous sodium chloride) is likely not pure sodium hydroxide (NaOH) but could be a mixture of sodium hydroxide, sodium chloride, and possibly some sodium carbonates or other impurities depending on the composition of your electrolyte solution.
The chlor-alkali process used in the industry for the production of NaOH and chlorine gas requires a large amount of electricity, and it's carefully controlled to avoid the formation of other products. The process you've carried out on a smaller scale with a 9V battery would not produce a pure substance.
Sodium hydroxide is highly soluble in water and typically forms a colorless solution. If you are observing a white residue, the concentration of the dissolved substances may have surpassed the solubility limits, leading to precipitation.
Alternatively, if the evaporation of water occurred over the 12 hours, the concentration of the solution could have reached a point where NaOH began to solidify out of the solution. However, this would be a very concentrated solution and would normally require heating the solution to dryness.
Typical industrial electrolysis for the chlor-alkali process includes a separation of the anode and cathode to prevent the recombination of chlorine and hydroxide ions. In your small-scale experiment, without these precautions, different reactions and products can occur, complicating the identification of the final product.