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Strong and Weak Bases

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The citric acid in fruits like oranges and lemons, tartaric acid in tamarind, malic acid in apples, lactic acid in milk and milk products, and hydrochloric acid in gastric juices are just a few examples of acids and bases found in nature. Many bases, such as lime water, can also be found. Many of these acids are used in our daily lives, such as vinegar or acetic acid in the kitchen, boric acid in laundry, baking soda in cooking, washing soda in cleaning, and so on.

Many acids and bases that we do not use in our daily lives are utilised in laboratories and industries, such as HCl, H2SO4, and NaOH, KOH, among others. The neutralisation process results in the creation of salt and water when these acids and bases are mixed in the proper quantities.

What are Bases?

The bitter taste and soapy texture of bases are two of their most prevalent characteristics. A base is a chemical that produces the hydroxyl ion (OH–) in water. Bases turn the colour of red litmus paper to blue. Bases can be categorized into two categories that are,

  • Strong Base
  • Weak Base

Strong Bases Definition

Strong bases completely ionise in water, resulting in a huge amount of OH ions. Sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and calcium hydroxide (Ca(OH)2) are just a few examples.

Weak Bases Definition

Weak bases partially ionise in water, resulting in a tiny number of OH ions. Magnesium hydroxide (Mg(OH)2) and ammonium hydroxide, for example (NH4OH).

What are Strong Bases?

A strong base is a fully ionic substance such as sodium hydroxide or potassium hydroxide. In solution, the molecule can be thought of as being completely broken up into metal ions and hydroxide ions. Each mole of sodium hydroxide in solution dissolves to produce a mole of hydroxide ions.

NaOH ⇢ Na+ + OH

Some strong bases, such as calcium hydroxide, aren’t very water-soluble. It makes no difference; whatever does dissolve is completely ionised into calcium and hydroxide ions. Because of its 100% ionisation, calcium hydroxide is nevertheless considered a strong base.

Calculating the pH of a strong base as,

pH = – log10 [H+]

How can a solution containing hydroxide ions have a pH since pH is a measure of hydrogen ion concentration? To understand this, you must first understand the ionic product for water. Wherever there is water, a balance is established. The following is a simplified version of this equilibrium:

H2O (l) ⇌ H+ (aq) + OH

With the addition of extra hydroxide ions, such as sodium hydroxide, the equilibrium still exists, but the point of equilibrium has shifted to the left, according to Le Chatelier’s Principle. Although there will be significantly fewer hydrogen ions than in pure water, hydrogen ions will still be present. The concentration of these is measured by the pH.

A description of how to calculate the pH of a strong base,

  • Work out the concentration of the hydroxide ions.
  • Use Kw to work out the hydrogen ion concentration.
  • Convert the hydrogen ion concentration to a pH

Examples of Strong Bases

Some Examples of the Strong Bases are,

Weak Bases

Weak bases are basic compounds that when dissolved in liquids do not entirely break down into their constituent ions. As a result, when the weak base is dissolved in a solution, some of it dissociates into hydroxide anions and the corresponding conjugate acid, while the rest stays undissociated inside the solution.

Ionization of a weak base is a form of equilibrium process in which a chemical equilibrium between the concentration of the undissociated base and its constituent ions is achieved inside the solution (the conjugate acid and the hydroxide anion). It’s vital to remember that a weak base’s conjugate acid is usually always 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 + H2O ⇌ BH+ + OH–

A lone pair of electrons in the basic molecule absorbs a proton from the water molecule in this equilibrium process, resulting in the creation of a hydroxide ion. The weaker the base, the greater the concentration of the equilibrium to the left. Similarly, the stronger the base, the higher the equilibrium concentration to the right.

Examples of Weak Bases

Some Examples of the Weak Bases are,

Summary of Strong and Weak Bases

  • The base that ionizes completely in an aqueous solution are called the Strong Base.
  • The base that ionizes partially in an aqueous solution are called the Weak Base.
  • Conjugate base of a strong acid is a weak base.
  • Conjugate base of a weak acid is a strong base.

Read More,

Sample Questions Strong and Weak Bases

Q1: Explain why a sodium sulphate aqueous solution is neutral and a sodium carbonate aqueous solution is basic in nature.

Answer:

Aqueous sodium sulphate solution is hydrolyzed to create sodium hydroxide and sulphuric acid, both of which are strong bases and acids. As a result, the aqueous solution is pH neutral. When sodium carbonate is dissolved in water, it is partially hydrolyzed, yielding sodium hydroxide and carbonic acid. 

Sodium hydroxide is now a strong base that is fully ionised and produces a significant number of hydroxide ions [OH– (aq)]. Carbonic acid, on the other hand, is a weak acid that is only minimally ionised and hence produces a modest number of hydrogen ions [H+ (aq)]. The combination is basic because it includes more hydroxide ions than hydrogen ions.

Q2: Is sodium hydroxide a base that isn’t very strong? Is there any reason to believe that?

Answer:

A strong base is sodium hydroxide, a chemical substance having the formula NaOH. This is due to the fact that when sodium hydroxide is dissolved in water, it almost completely ionises. The basic chemicals that do not totally ionise in water are known as weak bases. An example of a weak base is ammonia. When NH3 is dissolved in water, it interacts with the water molecules and dissociates into ammonium cation and hydroxide anions. However, some ammonia in the solution stays unionised.

Q3: Why do acids like HCl, HNO3, and others have acidic properties in aqueous solutions, but molecules like alcohol and glucose don’t?

Answer:

In aqueous solutions, ionised solutions such as HCl, HNO3, and others become acidic due to the presence of H+ ions. Because alcohol and glucose solutions do not generate any of these ions, they do not have acidic properties.

Q4: Why not keep curd and sour substances in brass and copper vessels?

Answer:

Acids in curd and sour things react with copper vessels and brass to generate hazardous chemicals.

Q5: Why does the colour of dry litmus paper not change when exposed to dry HCl gas?

Answer:

The acidic quality of dry HCl gas is not transmitted since it does not release H+ ions.

Strong and Weak Base-FAQs

1. What are the 5 Weak Bases?

5 weak bases are,

  • Al(OH)3 (Aluminium Hydroxide)
  • Pb(OH)2 (Lead Hydroxide)
  • Fe(OH)3 (Ferric Hydroxide)
  • Cu(OH)2 (Copper Hydroxide)
  • Zn(OH)2 (Zinc Hydroxide)

2. What are the 5 Strong Bases?

5 strong bases are,

  • Sodium Hydroxide(NaOH)
  • Potassium Hydroxide(KOH)
  • Lithium Hydroxide(LiOH)
  • Caclium Hydroxide{Ca(OH)2}
  • Barium Hydroxide{Ba(OH)2}

3. Is Water a Weak Base?

Pure water is a weak acid as well as a weak basic. This is because a little amount of water dissociates into protons and hydroxide anions, forming hydronium ions and hydroxide ions with the remaining water molecules.

4. Why Aqueous Solution of Acid Conducts Electricity?

Aqueous Solution of acid conducts electricity because aqueous solution of acid ionizes into ions and these ion conducts the electricty.



Last Updated : 17 Nov, 2023
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