The correct formula for calcium hydroxide is Ca(OH)2.
The Correct Answer and Explanation is:
Correct Answer:
The correct formula for calcium hydroxide is Ca(OH)₂.
Explanation:
Calcium hydroxide is an ionic compound formed from calcium and hydroxide ions. Understanding how this formula is derived involves looking at the charges of the ions involved.
Calcium is a metal found in Group 2 of the periodic table. Elements in Group 2 are known as alkaline earth metals, and they tend to lose two electrons to achieve a stable electron configuration. As a result, calcium forms a Ca²⁺ ion with a charge of +2.
The hydroxide ion is a polyatomic ion composed of one oxygen atom and one hydrogen atom, bonded together as OH⁻. This ion carries a charge of -1.
To write a neutral formula for calcium hydroxide, the total positive and negative charges must balance. Calcium has a +2 charge, and hydroxide has a -1 charge. Therefore, two hydroxide ions are needed to balance one calcium ion:
- One Ca²⁺ ion = +2
- Two OH⁻ ions = 2 × (−1) = −2
When combined, the charges cancel each other out, forming a neutral compound:
Ca²⁺ + 2OH⁻ → Ca(OH)₂
Note the use of parentheses around the OH group. This indicates that there are two entire hydroxide ions in the compound, not just two hydrogen atoms or two oxygen atoms. If the parentheses were not used and the formula were written as CaOH₂, it would imply two hydrogen atoms but only one oxygen, which is chemically incorrect.
Calcium hydroxide is commonly known as slaked lime and is often used in agriculture to neutralize acidic soils, as well as in construction and wastewater treatment. It appears as a white powder or colorless crystal and is only slightly soluble in water, forming a solution called limewater.
