Aldehydes and ketones that dissolve in water give netural solutions. They do not change the pH of the water. So if the water was pure to start with the pH is 7. Risk assessment Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website. For further guidance see our tutorial on Risk Assessment.