Calcium hydroxide

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A soft, white, alkaline powder. Calcium hydroxide, or slaked lime, is made by grinding quicklime (calcium oxide) with water; this forms a fine-grain precipitate. Calcium hydroxide absorbs carbon dioxide from the air forming calcium carbonate. It is used as a component in hydraulic cements because it will set underwater. Calcium hydroxide is also used to dehair hides, to kill insects, as a preservative in water paints and as a neutralizing agent in paper pulp solutions. A saturated solution of calcium hydroxide, called limewater, has a pH of 12.4.

Synonyms and Related Terms

calcium dihydroxide; slaked lime; calcium hydrate; lime hydrate; caustic lime; limewater

Other Properties

Soluble in glycerin, acids. Slightly soluble in water. pH = 12.4 (saturated solution)Insoluble in alcohols.

Composition Ca(OH)2
CAS 1305-62-0
Melting Point 580 (dec)
Density 2.08-2.34
Molecular Weight mol. wt. = 74.1

Hazards and Safety

Skin contact causes irritation.

International Chemical Safety Card

Additional Information

T.Schaeffer, V.Blythe-Hill, J.Druzik "Aqueous Light Bleaching of Paper: Comparison of Calcium Hydroxide and Magnesium Bicarbonate Bathing Solutions" JAIC, 35:219-238, 1996.

Sources Checked for Data in Record

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 505
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Book and Paper Group, Paper Conservation Catalog, AIC, 1984, 1989