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What is a Weak Base? Weak bases can be defined as basic substances that do not completely dissociate into their constituent ions when dissolved in solutions. Therefore, when dissolved in a solution, a part of the weak base dissociates into hydroxide anions and the relevant conjugate acid, and another part remains undissociated inside the solution. The ionization of a weak base is usually a type of equilibrium process in which a chemical equilibrium is established inside the solution between the concentration of the undissociated base and its constituent ions (the conjugate acid and the hydroxide anion). It is important to note that the conjugate acid of a weak base will almost always be a weak acid. Similarly, the conjugate base of a weak acid will act as a weak base. When a weak base is dissolved in water, the following type of equilibrium arises: B + H 2 O ⇌ BH+^ + OH– In this equilibrium reaction, a lone pair of electrons present in the basic molecule accepts a proton from the water molecule, resulting in the formation of a hydroxide ion. The greater the concentration of the equilibrium towards the left, the weaker the base. Similarly, the greater the equilibrium concentration towards the right, the stronger the base. Examples of Weak Bases Ammonia (NH 3 ) Ammonia is a chemical compound with the formula NH 3. It is a weak base which exists as a colourless gas under standard conditions for temperature and pressure. This gas is known to be characterized by its pungent smell. When ammonia is dissolved in water, the resulting solution (also referred to as ammonia water or ammonia solution) contains the ammonium cation (denoted by the chemical formula NH 4 +^ and the hydroxide anion. However, it is important to note that only a part of the dissolved ammonia dissociates into these ions.
Trimethylamine (N(CH 3 ) 3 ) Trimethylamine, often abbreviated to TMA, is a weak base with the chemical formula N(CH 3 ) 3. This compound can be prepared by reacting ammonia with methanol in the presence of a catalyst. It can also be produced from the reaction between paraformaldehyde and ammonium chloride. Pyridine (C 5 H 5 N) Pyridine is an organic compound with the chemical formula C 5 H 5 N. This chemical compound has a heterocyclic structure and is a weak base. The structure of pyridine is similar to that of benzene, with the exception that one of the methine groups is replaced with a single nitrogen atom. Under standard conditions for temperature and pressure, pyridine exists as a colourless liquid. It can also be noted that pyridine is a Lewis base and it has the ability to donate electron pairs to Lewis acids in order to form Lewis adducts. Questions on Weak Bases
Is sodium hydroxide a weak base? Why or why not?
Sodium hydroxide, a chemical compound with the formula NaOH, is known to be a strong base. This is because sodium hydroxide undergoes almost complete ionization when it is dissolved in water. Weak bases are the basic substances that do not completely ionize in water. An example of a weak base is ammonia. When NH 3 is dissolved in water, a part of it dissociates into ammonium cation and hydroxide anions by interacting with the water molecules. However, some ammonia remains unionized in the solution.
List 3 examples of weak bases
Three common examples of weak bases are listed below. Ammonia Pyridine Methylamine
Now that you have a general idea of pH and Kb values, let’s take a look at some of the most common examples of weak base and why they are important.
1. Hydroxylamine Formula: NH 2 OH Basicity (pKb): 8.0 5 Hydroxylamine is an oxygenated derivative of ammonia. Pure hydroxylamine is a colorless, crystalline solid that is soluble in water. Its inorganic salts are powerful reducing agents used to synthesize various polymers and as constituents of photographic developers. And they can act as antioxidants for fatty acids. Hydroxylamine is also an intermediate in the biological nitrification by microbes such as bacteria. In the semiconductor industry, it is often used to remove photoresists after lithography. Researchers are studying its nitrate salt called hydroxylammonium nitrate as a rocket propellant. Findings show that its solid form can be used to make solid propellants, and its water solution can be used to prepare monopropellants. Since hydroxylamine poses a dangerous fire hazard when exposed to intense heat, its potential uses must be evaluated carefully. The nature of the explosive hazard is still not well understood.
2. Trimethylamine Formula: N(CH 3 ) 3 Basicity (pKb): 4. Trimethylamine is a colorless tertiary amine in which every hydrogen atom is substituted by a methyl group. The central nitrogen atom is attached to three methyl groups in a trigonal pyramidal geometry. Trimethylamine is gas at room temperature but is highly soluble in water. It is generally sold as a 40% solution in water. At lower concentrations, it smells like a rotting fish. At higher concentrations, it smells like ammonia. Short-term inhalation of high concentrations or long-term inhalation of low concentrations can cause severe health problems. The compound is an excellent nucleophile, which means it can form bonds with electrophiles by donating an electron pair. It has several industrial applications — it is primarily used to synthesize plant growth
It is also used as a rocket fuel propellant — as the fuel burns, hydrazine decomposes into ammonia, nitrogen, and hydrogen gases, producing extensive amounts of heat energy. Hydrogen and nitrogen gases are forced out of the rocket through a nozzle to create thrust.
4. Zinc Hydroxide Formula: Zn(OH) 2 Basicity (pKb): 8. Zinc Hydroxide appears as a white solid and has a density of 3.05 g/cm^3. It occurs naturally in three rare minerals, namely ashoverite, sweetite, and wulfingite. It is also synthesized in the lab by mixing sodium hydroxide solution with a solution of any zinc salt. Like hydroxides of other metals, such as chromium, tin, beryllium, lead, and aluminum, zinc hydroxide is amphoteric. This means it can react both as an acid and as a base. It dissolves readily in a solution of a strong base (like sodium hydroxide) and also in a solution of strong acid (like hydrochloric acid). Zinc Hydroxide is mostly used as an absorbing agent in surgical dressings. It is also used as an intermediate for manufacturing pesticides and pigments.
5. Aluminum hydroxide Formula: Al(OH) 3 Basicity (pKb): 7. In its pure form, aluminum hydroxide is white granules or powder with a density of about 2.4 g/mL. Although it is not soluble in water, it quickly dissolves in strong bases and acids. Aluminum hydroxide has two unique properties: Amphoterism: This means it can react either as a base or acid. For instance, the OH in aluminum hydroxide can act as a weak base when mixed with a strong acid like hydrochloric acid. On the other hand, when it reacts with a strong base like sodium hydroxide, the OH in aluminum hydroxide acts as a weak acid. Polymorphism: This means the compound can exist in multiple forms. Aluminum hydroxide is known to have four different forms — bayerite, gibbsite, doyleite, and nordstrandite. Aluminum hydroxide is commonly used as an added ingredient in the antacid medication. It has been proven effective at treating heartburn,
Sodium bicarbonate reacts quickly with acids, producing carbon dioxide gas. That is why it is widely used to neutralize acid spills and undesirable acid solutions in chemical labs.
7. Pyridine Formula: C 5 H 5 N Basicity (pKb): 8. The structure of pyridine is quite similar to benzene, with one methine group replaced by a nitrogen atom. The presence of nitrogen (and its lone pair) in the benzene ring makes pyridine a unique compound in chemistry. Pyridine is a significantly weaker base than alkylamines and typical aliphatic tertiary amines. It is a water-soluble and highly flammable liquid with an unpleasant “fish-like” odor. Although pure pyridine has no color, the impure or older samples can appear yellow. This base is primarily used to dissolve other compounds and make various products, including dyes, paints, insecticides, medicines, food flavorings, vitamins, adhesives, and rubber products. It is also found in
many natural materials in the environment.
8. Ethylamine Formula: C 2 H 5 NH 2 Basicity (pKb): 3. Ethylamine is a corrosive primary amine. It is a weak base, which means it does not ionize completely in an aqueous solution to form ethyl- ammonium cations and hydroxide anions. An equilibrium is established between the non-ionized ethylamine molecules and the two ions that form due to its ionization. Like other primary amines, Ethylamine is an excellent solvent for lithium metal. Those solutions are used for Reducing unsaturated organic substances such as alkynes and naphthalenes. Furthermore, Ethylamine creates toxic nitrogen oxides during combustion. It is usually kept in a closed container; however, prolonged exposure to high temperatures may cause it to rupture violently.
Propylamine is mostly used for synthesizing and analyzing other chemicals.
10. Ammonium Hydroxide Formula: NH 4 OH Basicity (pKb): 4. Although ammonium hydroxide is a naturally occurring compound, it is also manufactured by humans for a number of reasons. It is made by dissolving ammonia into the water. The resulting liquid is colorless and has a pungent smell. The solution contains significant quantities of water and ammonia and smaller quantities of ammonium ion and hydroxide ion. Since ammonium hydroxide is not completely dissociated into ions, it’s a weak base. Its pH ranges between 7 and 10. This compound has several applications. In food, for example, ammonium hydroxide is used in concentrations of 0.7%, whereas households cleaners are made with 5-10% concentrations. It is also utilized in the conventional qualitative inorganic analysis as a complexant and base.
11. Methylamine Formula: CH 3 NH 2 Basicity (pKb): 3. Methylamine is a usual aliphatic primary amine, in which the NH 2 is connected to a carbon chain. All aliphatic primary amines, including this one, are stronger bases than ammonia. As you can see in the formula, the major difference between ammonia and methylamine is the presence of the CH 3 group in the latter. Since the alkyl group pushes electrons away from itself, a small negative charge builds up on the nitrogen atom, making the lone pair even more attractive towards hydrogen ions. And because ammonia doesn’t have any electron-donating group, it is a weaker base than methylamine (in which nitrogen is more negative, so it picks up H+more readily). Like ammonia, methylamine is a colorless gas or a liquid with a pungent odor. It can easily catch fire. Under prolonged exposure to high temperatures, methylamine containers may rupture violently. That’s why it must be handled with care.
Aniline is toxic in nature. It is rapidly absorbed by the skin, lungs, and gastrointestinal tract of experimental animals. However, it is widely used for synthesizing chemicals, especially agricultural chemicals, photographic chemicals, and dyes.
13. Ammonia Formula: NH 3 Basicity (pKb): 4. Ammonia has a great ability to form hydrogen bonds. When it is dissolved in water, it gains hydrogen ions from the water, producing ammonium and hydroxide ions. NH 3 (aq) + H 2 O <–> NH 4 +(aq) + OH–(aq) This reaction runs both ways, which means it is reversible. At any time during the reaction, nearly 99% of the substance still remains as ammonia molecules, and only 1% actually produces hydroxide ions. Since only a small part of ammonia is converted into hydroxide ions in solution, it is a weak base.
Ammonia is a building-block chemical used for manufacturing a wide range of products. Approximately 90% of the ammonia produced globally is used in fertilizer to enhance food production for billions of people. The rest is used in rubber and paper industries, wastewater treatment, and household cleaning products. Questions and Answer these topics: --
- Is Barium hydroxide a weak base? No. it’s a strong base like Potassium hydroxide and Sodium hydroxide. It dissolves very well in water to give barium ions (Ba2+) and hydroxyl ions (OH-). Furthermore, the solubility of barium hydroxide is greater than magnesium hydroxide, Beryllium hydroxide, and Calcium hydroxide. This is why it is a stronger base than other Group 2 metal hydroxides.
- What are some examples of strong bases? Strong bases are usually created from the hydroxides of alkali earth metals and alkali metals. Sodium hydroxide, Barium hydroxide, and Lithium hydroxide are some of the most common examples of strong bases. They can deprotonate weak acids. There also exist superbases that are even stronger. They are Group 1 sales of carbanions, amides, and hydrides. Their conjugate acid is extremely weak. Sodium amide, Butyl lithium, and Ethoxide ion are some of the examples of superbase. They are often used in organic chemistry as reagents.
