Gayathri Mani

HS-PS1-2

Arrhenius Bases Study Guide

An Arrhenius base is a base that gives hydroxide ions on dissolution in water.

INTRODUCTION

Have you ever wondered why soap is slippery? I hope you haven’t tried to taste soap, and we don’t even recommend you to taste it too. But do you know that soaps are bitter in taste? The soap contains a base, and bases are slippery and bitter to taste. The base present in soap is an Arrhenius base. But what are Arrhenius Bases? Let’s understand it and study the list of Arrhenius bases!

ARRHENIUS BASE

An Arrhenius base is a base that contains OH- i.e., a hydroxyl group. The OH group of bases ionizes in an aqueous solution. Now, is NaOH an Arrhenius base? Yes, NaOH is an example of an Arrhenius base. NaOH(aq) → Na+ + OH-

Arrhenius Base Source

When NaOH is added to water, it ionizes into Na+ and OH-. Some more examples of Arrhenius bases are: Ca(OH)₂, KOH, Mg(OH)₂, LiOH, etc. They all have one thing in common: they all ionize to give a metal cation and hydroxide ion(OH-).

Since Arrhenius bases give out OH- ions, they have pH > 7, the solution formed after the dissolution of an Arrhenius base is basic, but it may or may not be alkaline.

Bases like NaOH, KOH, LiOH are called alkali metal hydroxides as on dissolution in water; these give an alkaline solution. An alkaline solution is formed by a base that is soluble in water. But not all bases are alkaline.

Ca(OH)₂, Mg(OH)₂ also give alkaline solutions upon dissolution in water. Still, they are not as soluble as alkali earth metals, and thus they are not as strong as alkali metal hydroxides. These are called alkaline earth metal hydroxides.

Mg(OH)₂ ⇄ Mg²⁺ + 2OH-

Mg(OH)₂ doesn’t dissociate completely in water or is sparingly soluble in water. Do you know that the Kₛₚ of Mg(OH)₂ is too low as 10-11 at 25℃? It isn’t as strong as alkali metal hydroxides and is used as in antacid and laxatives.

On the other hand, alkali metal hydroxides such as KOH, NaOH are completely soluble in water and can cause severe burns.

Do you know that NaOH is used to make soaps, rayon paper, food processing fields such as making ice creams, pretzels, preserving olives and in dyes, paint removal, and petroleum products?

CONCLUSION:

  • An Arrhenius base is a base that gives hydroxide ions on dissolution in water.
  • Alkali metals hydroxides are strong bases, while alkaline earth metal hydroxides are weak bases.

FAQs:

1. What is an Arrhenius base?

An Arrhenius base is a base that gives hydroxide ions on dissolution in water.

2. Out of NH₃ and NaOH, which one is an Arrhenius base?

NaOH is an Arrhenius base as it will give OH- on dissolution in water.

3. Out of NaOH and Mg(OH)₂, which one is a stronger Arrhenius base?

Mg(OH)₂ doesn’t dissociate completely in water and is a weak base in comparison to NaOH.

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SOURCES:

  1. Sodium Hydroxide: https://www.cdc.gov/niosh/topics/sodium-hydroxide/default.html#:~:text=Sodium%20hydroxide%20is%20used%20to,commercial%20drain%20and%20oven%20cleaners. Accessed 7th March 2022.
  2. Arrhenius Bases: https://www.ck12.org/c/chemistry/arrhenius-bases/lesson/Arrhenius-Bases-CHEM/. Accessed 7th March 2022.