Question

Write down the chemical formula of Magnesium hydroxide.

Answer 1

Hint: To answer this question, you must recall the chemical symbols of various elements and compounds. To write the chemical formula you must also be familiar with valencies. Magnesium is an alkaline earth metal or a group II metal in the periodic table.

Complete step by step solution:
Magnesium hydroxide is a white colored inorganic salt which is poorly soluble in water. It is obtained as a precipitate when an ionic compound of magnesium metal, say magnesium sulphate reacts with alkaline water.
Magnesium is represented by the symbol $Mg$ and it has two valence electrons. It loses the two electrons readily to form a divalent cation having a completely filled second shell. The magnesium cation is represented as $M{g^{2 + }}$
Hydroxide ion is a negatively charged ion carrying a single charge. It is represented by $O{H^ - }$.Thus, to neutralize the $ + 2$ charge on magnesium ions, we need two hydroxide ions.
The chemical formula of magnesium sulphate is thus given as $Mg{\left( {OH} \right)_2}$.

Additional information:
Magnesium hydroxide is a weak base due to its low solubility in water. It has a molecular mass of $58{\text{ g/mol}}$ and is commonly known as milk of magnesia. Due to its mildly basic character, it is commonly used as an antacid and as a laxative. It also has smoke suppressing properties and is a majorly used flame retardant.

Note:
Care should be taken that you are not confused between oxide and hydroxide ion. Oxide ion is an oxygen ion carrying a double negative charge and represented as ${O^{2 - }}$ while hydroxide ion is formed when a proton, i.e., hydrogen cation adds to the oxide ion giving a single negatively charged $O{H^ - }$ ion.