Properties of water equal to that of the hydrogen ion (), which gives a pH of 7 at 25 °C. Action of water on rock over long periods of time typically leads to weathering and water erosion, physical processes that convert solid rocks and minerals into soil and sediment, but under some conditions chemical reactions with water occur as well, resulting in metasomatism or mineral hydration, a type of chemical alteration of a rock which produces clay minerals. It also occurs when Portland cement hardens. Water ice can form clathrate compounds, known as clathrate hydrates, with a variety of small molecules that can
Water-reactive substances Water-reactive substances Water-reactive substances are those that spontaneously undergo a chemical reaction with water, as they are highly reducing in nature. Notable examples include alkali metals, sodium through caesium, and alkaline earth metals, magnesium through barium. Some water-reactive substances are also pyrophoric, like organometallics and sulphuric acid, and should be kept away from moisture. The use of acid-resistant gloves and face shield are required and should be handled in fumehoods. Water-reactive substances are classified as R2 under the UN classification system and as Hazard 4.3 by the United States Department of Transportation. All chemicals that react vigorously with water or