Alkaline substances are primarily aqueous solutions such as ammonia or caustic soda. They are alkaline if their pH value is greater than 7. This means that the concentration of hydroxide ions (OH-) is higher than that of oxonium ions (H3O+). One of the properties of alkaline substances is that they can burn the skin or eyes on contact, which is why it is advisable to wear protective clothing (e.g. goggles and gloves) when using them.
