Common Hydroxide Compounds and Their Applications
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 What is Hydroxide? Formula, Charge & Examples
1. What is the hydroxide ion and what is its chemical formula?
The hydroxide ion is a diatomic, polyatomic ion consisting of one oxygen atom and one hydrogen atom held together by a covalent bond. Its chemical formula is OH⁻. The superscript '⁻' indicates that the ion has a net negative charge of one.
2. How is the hydroxide ion (OH⁻) formed?
The hydroxide ion can be formed in several ways. Most commonly in chemistry, it forms when a water molecule (H₂O) loses a proton (H⁺), a process known as deprotonation. It also forms when alkali metal hydroxides (like NaOH) or other bases dissolve in water, dissociating into a positive metal ion and a negative hydroxide ion (OH⁻).
3. Why does the hydroxide ion have a negative charge?
The negative charge on the hydroxide ion (OH⁻) arises from its atomic structure. An oxygen atom has 6 valence electrons and a hydrogen atom has 1. In the OH⁻ ion, they form a covalent bond by sharing electrons. However, the ion as a whole has gained an extra electron from another atom (like sodium in NaOH). This gives the oxygen atom a full octet and results in a net negative charge of -1 for the entire ion.
4. According to the CBSE syllabus, is the hydroxide ion (OH⁻) acidic or basic?
According to the Arrhenius theory of acids and bases, a substance that produces hydroxide ions (OH⁻) when dissolved in water is a base. Therefore, the hydroxide ion is the primary species responsible for making a solution basic or alkaline. Its presence increases the pH of a solution above 7.
5. What is the difference between a hydroxide ion (OH⁻) and a hydroxyl radical (•OH)?
Although both contain one oxygen and one hydrogen atom, they are fundamentally different chemical species.
- The hydroxide ion (OH⁻) is a stable ion with a full outer shell of electrons and a negative charge. It is the key component that defines a substance as a base.
- The hydroxyl radical (•OH) is a neutral molecule but is extremely reactive and unstable because it has an unpaired electron. It is a powerful oxidising agent and is not typically found freely in solutions like the hydroxide ion is.
6. What is the valency of the hydroxide ion?
The valency of the hydroxide ion (OH⁻) is 1. Since it carries a net charge of -1, it will combine with one cation having a +1 charge (like Na⁺ to form NaOH) or with cations having higher charges in corresponding ratios (like Ca²⁺ to form Ca(OH)₂).
7. How are compounds containing hydroxide, like magnesium hydroxide (Mg(OH)₂), named?
Compounds containing the hydroxide ion are generally named by stating the name of the positive ion (cation) first, followed by the word "hydroxide". For example:
- NaOH: Sodium hydroxide
- KOH: Potassium hydroxide
- Mg(OH)₂: Magnesium hydroxide
- Al(OH)₃: Aluminium hydroxide
8. What are some important industrial and everyday applications of hydroxide compounds?
Hydroxide compounds are vital in many areas. For example, sodium hydroxide (NaOH), also known as caustic soda, is used in manufacturing paper, soap, and detergents. Calcium hydroxide (Ca(OH)₂) is used in food processing, water treatment, and as a component of mortar. Magnesium hydroxide (Mg(OH)₂) is commonly used as an antacid (milk of magnesia).
9. How does the hydroxide ion participate in a neutralisation reaction?
In a neutralisation reaction, a base (which provides OH⁻ ions) reacts with an acid (which provides H⁺ or H₃O⁺ ions). The hydroxide ion (OH⁻) from the base combines directly with the hydrogen ion (H⁺) from the acid to form a neutral water molecule (H₂O). This reaction, H⁺ + OH⁻ → H₂O, is the fundamental chemical process of neutralisation.
10. What is the key difference between the hydroxide ion (OH⁻) and the hydronium ion (H₃O⁺)?
They are essentially opposites in the context of acid-base chemistry as per the CBSE curriculum.
- The hydroxide ion (OH⁻) is characteristic of bases and makes a solution alkaline. It is formed when a water molecule loses a proton.
- The hydronium ion (H₃O⁺) is characteristic of acids and makes a solution acidic. It is formed when a water molecule gains a proton (H⁺).
