What Is Hydroxide Definition Formula Formation Reactions and Examples
Hydroxide is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
What is Hydroxide in Chemistry?
A hydroxide refers to the negatively charged ion OH⁻, formed from one oxygen and one hydrogen atom joined by a covalent bond with an extra electron. This concept appears in chapters related to acids and bases, chemical reactions, and inorganic compounds, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of hydroxide is OH⁻. It consists of one oxygen atom and one hydrogen atom, joined covalently, with an overall negative charge. Hydroxide belongs to the class of inorganic ions called anions and is found in many important compounds like sodium hydroxide and calcium hydroxide.
Preparation and Synthesis Methods
Hydroxide ions are produced when bases dissolve in water—a process called dissociation. For example, dissolving sodium hydroxide (NaOH) releases OH⁻ ions.
In the laboratory, metal hydroxides like copper(II) hydroxide can be prepared by reacting a soluble salt (such as copper sulfate) with sodium hydroxide, resulting in a precipitation reaction. Industrially, large amounts of sodium hydroxide are made by the chloralkali process.
Physical Properties of Hydroxide
The hydroxide ion (OH⁻) is colorless in solution, has a monoisotopic mass of about 17 g/mol, and is highly soluble in water. Metal hydroxides vary in appearance—some are white solids (like sodium hydroxide), others are gels (like aluminum hydroxide). Hydroxide ions give solutions their slippery, soapy feel and turn red litmus paper blue, indicating basicity.
Chemical Properties and Reactions
Hydroxide ions are strong bases, meaning they readily accept protons (H⁺) to form water. When hydroxide reacts with acids, a neutralization reaction occurs, producing water and a salt.
Hydroxides can also participate in precipitation, redox, and hydrolysis reactions, making them important for many synthetic and environmental processes.
Frequent Related Errors
- Confusing hydroxide ions with neutral molecules like water or hydroxyl groups (-OH in organic chemistry).
- Ignoring the negative charge of hydroxide, which is crucial for identifying its base behavior.
Uses of Hydroxide in Real Life
Hydroxide compounds are widely used in making soaps, detergents, cleaning agents, paper, and textiles. Sodium hydroxide is common in household drain cleaners.
In toothpaste, hydroxide helps balance acidity and protect teeth. Metal hydroxides are also used to purify water and treat acid spills.
Relation with Other Chemistry Concepts
Hydroxide ions are closely related to the study of bases and acid-base neutralization. They also support the understanding of pH, chemical reactions, and electrolytes in water. Recognizing hydroxide in chemical equations aids in balancing reactions and predicting products.
Step-by-Step Reaction Example
- Start with the reaction setup.
Mix hydrochloric acid (HCl) and sodium hydroxide (NaOH) in water. - Write the balanced equation.
HCl + NaOH → NaCl + H₂O - Explain each intermediate or by-product.
H⁺ from HCl reacts with OH⁻ from NaOH, producing water.
Na⁺ combines with Cl⁻ to form sodium chloride (table salt).
Lab or Experimental Tips
Remember that hydroxide solutions feel slippery and can be corrosive—always use gloves and goggles during experiments. Vedantu educators recommend using red litmus paper for quick identification: it turns blue in the presence of hydroxide ions.
Try This Yourself
- Write the IUPAC name of NaOH.
- Explain why the addition of Ca(OH)₂ to acidic soil makes it suitable for crops.
- Give two everyday examples where hydroxide is used.
Final Wrap-Up
We explored hydroxide—its structure, properties, reactions, and real-life importance. For more in-depth explanations and exam-prep tips, explore live classes and notes on Vedantu.
| Common Hydroxide | Formula | Main Use |
|---|---|---|
| Sodium Hydroxide | NaOH | Soap, detergents, cleaning agents |
| Potassium Hydroxide | KOH | Batteries, soaps |
| Calcium Hydroxide | Ca(OH)₂ | Soil neutralization, water treatment |
| Magnesium Hydroxide | Mg(OH)₂ | Antacid, laxative |
Explore more: Sodium Hydroxide | Types of Chemical Reactions
FAQs on Hydroxide in Chemistry Structure Properties and Reactions
1. What is a hydroxide ion?
A hydroxide ion is a negatively charged ion with the formula OH-, consisting of one oxygen atom bonded to one hydrogen atom. It carries a −1 charge because oxygen has gained an extra electron. Hydroxide ions are characteristic of bases in aqueous solutions and are responsible for alkaline properties such as turning red litmus paper blue and having a pH greater than 7.
2. What is the formula for hydroxide?
The chemical formula for hydroxide is OH-. It is a polyatomic ion made of one oxygen atom covalently bonded to one hydrogen atom with an overall −1 charge. This ion commonly appears in compounds such as NaOH (sodium hydroxide) and Ca(OH)2 (calcium hydroxide).
3. What is the difference between hydroxide and hydroxyl?
The key difference is that hydroxide is the ion OH-, while hydroxyl is the neutral functional group –OH in organic compounds.
- Hydroxide (OH-): Negatively charged ion found in bases like NaOH.
- Hydroxyl (–OH): Neutral group attached to carbon atoms in alcohols such as ethanol (C2H5OH).
4. How are hydroxide ions formed in water?
Hydroxide ions are formed in water when a base dissociates or when water undergoes self-ionization.
- Dissociation of a base: NaOH(aq) → Na+(aq) + OH-(aq)
- Self-ionization of water: 2H2O(l) ⇌ H3O+(aq) + OH-(aq)
5. What are some common hydroxide compounds?
Common hydroxide compounds are ionic bases that contain the OH- ion combined with a metal cation.
- NaOH – Sodium hydroxide (strong base)
- KOH – Potassium hydroxide (strong base)
- Ca(OH)2 – Calcium hydroxide (slightly soluble base)
- Mg(OH)2 – Magnesium hydroxide (weakly soluble base)
6. Is hydroxide a strong or weak base?
Hydroxide itself is a strong base because it readily accepts protons (H+) to form water. According to the Arrhenius definition, bases produce OH- in aqueous solution. Compounds like NaOH and KOH are strong bases because they completely dissociate in water, while some hydroxides like Mg(OH)2 are considered weak due to low solubility rather than weak ionization.
7. How do hydroxide ions react with acids?
Hydroxide ions react with acids in a neutralization reaction to form water and a salt. The net ionic equation is:
- H+(aq) + OH-(aq) → H2O(l)
- HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
8. How do you calculate pOH from hydroxide ion concentration?
The pOH is calculated using the formula pOH = −log[OH-].
- Step 1: Determine the hydroxide ion concentration in mol L−1.
- Step 2: Take the negative logarithm of that value.
9. Why do hydroxide solutions have a pH greater than 7?
Hydroxide solutions have a pH greater than 7 because they contain excess OH- ions that reduce the concentration of H+ ions. In aqueous solutions at 25°C, pH + pOH = 14. When [OH-] increases, pOH decreases, causing the pH to increase above 7. This makes the solution basic or alkaline.
10. What is the valency and charge of hydroxide?
The hydroxide ion has a valency of 1 and a charge of −1. Its formula is OH-, meaning it can combine with one positively charged ion such as Na+ or half of a Ca2+ ion in forming compounds like NaOH and Ca(OH)2. The single negative charge determines how many hydroxide ions are needed to balance a metal cation in ionic compounds.
