Is NaOH a base or an acid? — Are you a strong or weak person?

A metal hydroxide is sodium hydroxide. Caustic soda is the most popular name for it.

NaOH is a corrosive solid that is water soluble.

The electrolysis of brine solution is the most prevalent technique of producing NaOH.

The chemical sodium hydroxide (NaOH) is extremely useful.

Based on their varied qualities, substances are classed as acids, bases, or salts.

We will learn about several ideas that explain the meaning of acids and bases, as well as the nature of sodium hydroxide, in this article.

Is NaOH an acid or a basic, then? Because NaOH entirely dissolves in water, it releases hydroxide ions (together with sodium ions), which are responsible for an aqueous solution’s basic character. A basic compound is one that releases OH- ions in an aqueous solution. NaOH has a pH of roughly 12 and is classified as a strong base.

What is the function of NaOH as a base?

Acids and bases are defined differently by different scientists. We’ll concentrate on three major theories.

Theorem of Arrhenius

According to this idea, an acid is a chemical that loses H+ ions in aqueous solution, whereas a base is a substance that loses OH– ions in aqueous solution.

When NaOH is dissolved in water, it disintegrates into Na+ and OH– ions. It is categorised as an Arrhenius base because it releases hydroxide ions in water.

When the solvent is water, this idea holds true.

Theorem of Lewis

According to this hypothesis, a Lewis acid is a material that obtains an electron pair, while a Lewis base is a substance that loses an electron pair.

Lewis acids (such as BF3) are electron-deficient chemicals, whereas Lewis bases (such as BF3) are electron-rich ones. (For example, NH3)

In the case of NaOH, a hydroxide ion is formed, which possesses a lone pair of electrons that can be accepted by other electron-deficient molecules.

Bronsted-Lowry Theory is a theory proposed by Bronsted and Lowry.

According to this hypothesis, an acid is a chemical that loses a proton, whereas a base is a substance that gets a proton.

When NaOH reacts with an acid, it takes on the acid’s proton and behaves like a Bronsted-Lowry base. OH– accepts the proton in NaOH. As a result, a stronger base is associated with a larger concentration of hydroxide ions.

As a result, NaOH has been classed as a base by all three primary theories.

In water, all bases are insoluble.

Alkali are bases that are soluble in water. An alkali is sodium hydroxide.

What makes NaOH such a powerful base?

According to the Arrhenius theory, a base can be classed as strong or weak depending on the amount of hydroxide ions released when it dissolves in water.

When a substance dissociates entirely in water, releasing hydroxide ions and counterions, it is referred to as a strong base.

For example, if you take 1 mole of a strong base, you’ll get 1 mole of hydroxide ions and 1 mole of counter ions. There is no such thing as a strong base that isn’t detached.

In the case of a weak base, water does not allow complete dissociation. For example, if 1 mole of a weak base is dissolved in water, only around 1 mole of hydroxide ions and counter ions is released.

There would be some undissociated base remained, which would be in balance with the undissociated base.

When NaOH is dissolved in water, it separates into two ions: Na+ and OH–. This is true for both strong and weak foundations. The distinction is in the degree of dissociation.

NaOH (aq) 🡺 Na(aq) + OH(aq)

Keq = [Na+][OH]/[NaOH]

Keq * [NaOH] = k= [Na+][OH]

The concentration of hydroxide ions in a strong base is very high, but the concentration of the undissociated form is much lower. For strong bases, this means that kb is huge.

NaOH completely dissociates, leaving no molecule in an undissociated state. As a result, it is a solid foundation.

Strong Base vs. Weak Base

Strong baseWeak base
It dissociates completely into hydroxide ions and the counterions (cations) on dissolving in water.It does not dissociate entirely into hydroxide ions and the counterions on dissolving in water.
All the molecules of the base are dissociated.Some base molecules are dissociated, and others remain in equilibrium with the undissociated base.
For a given concentration, they are more reactive.For a given concentration, they are less reactive.
pH value is more than 7 and nearer to 14.pH value lies in the range of 7-14. The exact value depends on the concentration.
It has a high pka value and low pkb value.It has a low pka value and a high pkb value.
It is a strong electrolyte.It is a weak electrolyte.
For example, NaOH, KOH, etc.For example, NH4OH, NH3, etc.

The equilibrium is expressed as- for weak bases like NH4OH.


Keq = [NH4+][OH-]/[ NH4OH]

kb = Keq * [ NH4OH] = [NH4+][OH-]

Because all of the base is not dissociated to create hydroxide ions, Kb is minimal for weak bases.

Why isn’t NaOH considered an acid?

In water, NaOH dissociates to form hydroxide ions, which can receive a proton.

In an aqueous solution, acid dissociates to release H+ ions, but NaOH releases hydroxide ions instead, according to the Arrhenius idea.

In an aqueous solution, acid releases a proton, but hydroxide ions receive a proton instead of losing one, according to the Bronsted-Lowry principle.

Acids absorb an electron pair and are electron poor, whereas NaOH loses an electron pair and is electron rich, according to the Lewis idea.

A neutralisation reaction occurs when an acid combines with a base to produce salt and water, but it does not occur when an acid reacts with another acid.

HCl is an acid, while KOH is a basic, as we all know. NaOH forms NaCl and water when it combines with an acid like HCl, but it does not neutralise when it reacts with another base like KOH.

As a result, NaOH is not an acid.

NaOH Conjugate Acid

The species generated when an acid loses a proton is known as the acid’s conjugate base. A weak conjugate base possesses a strong acid, and vice versa.

The species generated when a base obtains a proton is known as the base’s conjugate acid. A weak conjugate acid possesses a strong base, and vice versa.

The difference between conjugate acid-base pairs can be described as a proton difference.

Acid + Base —–> acid’s conjugate base + the base’s conjugate acid

A strong base is NaOH. A proton is added to the base. The basic character of NaOH is due to hydroxide ions, with sodium ion acting as a bystander.

The term “spectator” refers to the audience in general. As a result, sodium ions play no role in the process; they are just present in the solution to balance the charges.

NaOH generates water and sodium ions when it gains a proton. Water, the conjugate acid of NaOH, is formed when hydroxide ions accept a proton.

Because sodium hydroxide is such a strong base, the conjugate acid should be weak, and water is just a weak acid.

Water, or H2O, is the conjugate acid of NaOH.

The relative strength of acid and base is determined by the conjugate acid-base idea.

What is the significance of NaOH as a Lewis base?

Lewis base is an electron-rich substance that can contribute its electron pairs to a lewis acid or another electron-deficient chemical. For Lewis theory to work, the solvent does not have to be water.

Hydroxide ions are present in NaOH. On hydroxide ions, there are lone pairs and formal charges that can be given to an electron-deficient species, such as a proton (H+), to produce water.

As a spectator ion, sodium-ion is present. NaOH operates as a Lewis base, while HCl acts as a Lewis acid, in a simple neutralisation process between NaOH and HCl.

NaOH’s pH

The pH scale can be used to determine the amount of [H+] in a solution. It’s calculated with the following formula:

-log([H+]) = pH

A high concentration of H+ indicates a strongly acidic solution with a lower pH.

A solution with a pH of 2 is acidic, whereas one with a pH of 4 is alkaline.

The pH scale ranges from 0 to 14 at 25°C.

• When the pH of a substance reaches 7, it is considered neutral.

• An acidic material has a pH of 7.

• A substance is basic when its pH is greater than 7.

Because NaOH is a strong base, its pH is higher than 7 and closer to 14.

We need to know the concentration of hydroxide ions in order to make a base, therefore we have pOH.

pOH is equal to -log([OH–])

pOH=14 pH + pH + pH + pH + pH + pH + pH + pH +

If a substance’s pH is 13, the pOH value is 1.

By measuring the pH of a solution, we may quickly determine the strength and concentration of hydroxide ions.

A 0.1 M of NaOH, for example, has a pOH of 1 (pOH= -log (0.1)) and a pH of 13. Alternatively, we can use antilog to compute pOH and pH if we know the pH of a solution is 13.

What factors influence a base’s strength?

  1. Atomic Size: A large atom with strong polarizability is more basic than a smaller atom because it can easily donate electron pairs.

KOH, for example, is more basic than NaOH because K is easier to ionise due to its bigger size, and hydroxide is discharged more quickly.

  1. Electron Availability: When electrons are conjugated with other atoms, their availability for donating to another species drops. The basic strength of a compound is diminished as a result of the reduced availability.

Because lone pairs of nitrogen in aniline are delocalized, methylamine is more basic than aniline.

  1. Electronegativity: The basic strength is affected by the electronegativity of the atom contributing electrons, as electronegative atoms transfer electrons more slowly and are less basic.

CH3–, for example, is a more powerful base than F–.

NaOH’s acidity

On ionisation, a base’s acidity is defined as the number of hydroxide ions that may be created from one molecule of the base.

The number of hydrogen ions that a specific acid can produce when ionised is known as its basicity.

One molecule of NaOH produces one molecule of OH–, which can react with one H+ ion to make one molecule of water. As a result, sodium hydroxide is classified as a monoacidic base.

The NaOH Litmus Test

Litmus paper is a type of test paper that is used

Litmus is a natural indicator that can be used to determine if a substance is acidic, basic, or neutral. Lichens provide the litmus solution.

When the solution is neither acidic nor basic, the litmus dye turns purple.

Litmus sheets come in two colours: red and blue. Acids turn blue litmus red, while bases turn red litmus blue. Red litmus paper is unaffected by acids, while blue litmus paper is unaffected by bases.

NaOH is a strong base that turns red litmus paper blue while having no impact on blue litmus paper.


In water, NaOH is a strong base because it dissociates entirely to generate hydroxide ions, which can take protons to make water.

NaOH has a pH of above 7 and close to 14.

Water is the conjugate acid of NaOH.

NaOH is a monobasic compound.

A weak base does not completely dissociate, and the pH ranges from 7 to 14.

To determine if a substance is acidic, basic, or neutral, use litmus paper. Litmus glows blue when it comes into contact with NaOH.

Good luck with your studies!!

Read more: What is the difference between polar and nonpolar methanol?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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