Acids and bases

August 10, 2023Posted by ctliadmineLearning Cafe, eLearning scienceacids, acids and bases, Arrhenius, bases, Bronsted-Lowry, chemistry, pH, pOH

[vc_row equal_height=”yes” rtl_reverse=”yes”][vc_column width=”2/3″][ultimate_heading main_heading=”Acids and bases” heading_tag=”h1″ main_heading_color=”#090a0f” alignment=”left”][/ultimate_heading][vc_empty_space height=”45px”][vc_column_text]Acid-base chemistry is a fundamental branch of chemistry that deals with the properties, reactions, and interactions of acids and bases.

[/vc_column_text][/vc_column][vc_column width=”1/3″ css=”.vc_custom_1680558300810{border-top-width: 1px !important;border-right-width: 1px !important;border-bottom-width: 1px !important;border-left-width: 1px !important;border-left-color: #dddddd !important;border-left-style: solid !important;border-right-color: #dddddd !important;border-right-style: solid !important;border-top-color: #dddddd !important;border-top-style: solid !important;border-bottom-color: #dddddd !important;border-bottom-style: solid !important;border-radius: 10px !important;}”][ultimate_heading main_heading=”Jump to” heading_tag=”h3″ main_heading_color=”#090a0f” alignment=”left”][/ultimate_heading][vc_wp_custommenu nav_menu=”2617″][vc_separator][vc_column_text]

Grow your competencies

Check out The Hive for more info[/vc_column_text][/vc_column][/vc_row][vc_row el_id=”Arrhenius acids and bases”][vc_column][vc_empty_space height=”45px”][vc_separator][vc_empty_space height=”45px”][ultimate_heading main_heading=”Arrhenius acids and bases” main_heading_color=”#090a0f” alignment=”left”][/ultimate_heading][vc_column_text]The Arrhenius theory defines acids and bases based on their behaviour in aqueous solutions. According to the Arrhenius theory, acids and bases are defined as follows:

Arrhenius acids

Acids are substances that, when dissolved in water, increase the concentration of hydrogen ions (H⁺) in the solution.
They are proton donors, releasing hydrogen ions into the solution.

[/vc_column_text][vc_tta_accordion shape=”square” active_section=”” collapsible_all=”true”][vc_tta_section title=”Example of an Arrhenius acid” tab_id=”1691615315541-55226b84-e3f5″][vc_column_text]Hydrochloric acid (HCl) dissolved in water dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻).

HCl → H⁺ + Cl⁻[/vc_column_text][/vc_tta_section][/vc_tta_accordion][vc_empty_space height=”45px”][vc_column_text]

Arrhenius bases

Bases are substances that, when dissolved in water, increase the concentration of hydroxide ions (OH⁻) in the solution.
They are proton acceptors, attracting hydrogen ions from the solution.

[/vc_column_text][vc_tta_accordion shape=”square” active_section=”” collapsible_all=”true”][vc_tta_section title=”Example of an Arrhenius base” tab_id=”1691615465217-f5116118-a7df”][vc_column_text]Sodium hydroxide (NaOH) dissolved in water dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻).

NaOH → Na⁺ + OH⁻[/vc_column_text][/vc_tta_section][/vc_tta_accordion][vc_empty_space height=”45px”][vc_column_text]According to the Arrhenius theory, in an aqueous solution, a reaction between an acid and a base results in the formation of water and a salt. This reaction is known as an acid-base neutralization reaction.[/vc_column_text][vc_tta_accordion shape=”square” active_section=”” collapsible_all=”true”][vc_tta_section title=”Example of an acid-base neutralization reaction” tab_id=”1691615965771-4f022c74-f522″][vc_column_text]The reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) results in the formation of water (H₂O) and sodium chloride (NaCl).

HCl + NaOH → H₂O + NaCl[/vc_column_text][/vc_tta_section][/vc_tta_accordion][vc_empty_space height=”45px”][vc_column_text]It’s important to note that the Arrhenius theory focuses specifically on aqueous solutions and the presence of hydrogen ions (H⁺) and hydroxide ions (OH⁻). While the Arrhenius theory provides a useful framework for understanding acids and bases in water, it has limitations when considering non-aqueous systems or substances that do not produce hydrogen ions or hydroxide ions.[/vc_column_text][/vc_column][/vc_row][vc_row el_id=”Bronsted-Lowry acids and bases”][vc_column][vc_empty_space height=”45px”][vc_separator][vc_empty_space height=”45px”][ultimate_heading main_heading=”Bronsted-Lowry acids and bases” main_heading_color=”#090a0f” alignment=”left”][/ultimate_heading][vc_column_text]Brønsted-Lowry acid and base theory provides a broader definition of acids and bases compared to the Arrhenius theory. According to the Bronsted-Lowry theory, acids and bases are defined in terms of proton (H⁺) transfer.

Here is an explanation of Bronsted-Lowry acids and bases:

Bronsted-Lowry acid:

An acid is a species that donates a proton (H⁺) to another species.
In other words, an acid is a substance that can release a hydrogen ion (H⁺) in a chemical reaction.

[/vc_column_text][vc_tta_accordion shape=”square” active_section=”” collapsible_all=”true”][vc_tta_section title=”Example of a Bronsted-Lowry acid” tab_id=”1691615557942-43fbc353-08c4″][vc_column_text]Hydrochloric acid (HCl) can donate a proton to water (H₂O), forming hydronium ions (H₃O⁺): HCl + H₂O → H₃O⁺ + Cl⁻[/vc_column_text][/vc_tta_section][/vc_tta_accordion][vc_empty_space height=”45px”][vc_column_text]

Bronsted-Lowry base:

A base is a species that accepts a proton (H⁺) from another species.
In other words, a base is a substance that can combine with a hydrogen ion (H⁺) in a chemical reaction.

[/vc_column_text][vc_tta_accordion shape=”square” active_section=”” collapsible_all=”true”][vc_tta_section title=”Example of a Bronsted-Lowry base” tab_id=”1691615648872-4cf0f8b4-277d”][vc_column_text]Ammonia (NH₃) can accept a proton from water (H₂O), forming ammonium ions (NH₄⁺): NH₃ + H₂O → NH₄⁺ + OH⁻[/vc_column_text][/vc_tta_section][/vc_tta_accordion][vc_empty_space height=”45px”][vc_column_text]According to the Bronsted-Lowry theory, acid-base reactions involve the transfer of protons between the acid and the base. The acid donates a proton to the base, resulting in the formation of a conjugate acid and conjugate base pair.

Conjugate Acid:

The species formed after the base accepts a proton (H⁺) from an acid.
It is the result of protonation of the base.

Conjugate Base:

The species formed after the acid donates a proton (H⁺) to a base.
It is the result of deprotonation of the acid.

[/vc_column_text][vc_tta_accordion shape=”square” active_section=”” collapsible_all=”true”][vc_tta_section title=”Example of a conjugate acid and conjugate base pair” tab_id=”1691617462600-836189c4-6e93″][vc_column_text]In the reaction between hydrochloric acid (HCl) and water (H₂O), HCl acts as an acid (donating a proton) and forms a conjugate base, chloride ion (Cl⁻). Water acts as a base (accepting a proton) and forms a conjugate acid, hydronium ion (H₃O⁺).

HCl + H₂O → H₃O⁺ + Cl⁻[/vc_column_text][/vc_tta_section][/vc_tta_accordion][/vc_column][/vc_row][vc_row el_id=”pH and pOH”][vc_column][vc_empty_space height=”45px”][vc_separator][vc_empty_space height=”45px”][ultimate_heading main_heading=”pH and pOH” main_heading_color=”#090a0f” alignment=”left”][/ultimate_heading][vc_column_text]pH and pOH are logarithmic scales used to measure the acidity or alkalinity (basicity) of a solution. They provide a way to quantify the concentration of hydrogen ions (H⁺) or hydroxide ions (OH⁻) in a solution.

pH:

The pH scale measures the acidity or alkalinity of a solution based on the concentration of hydrogen ions (H⁺).
It is a logarithmic scale ranging from 0 to 14.
A pH value below 7 indicates an acidic solution, where the concentration of H⁺ ions is higher.
A pH value of 7 represents a neutral solution, where the concentrations of H⁺ and OH⁻ ions are equal (as in pure water).
A pH value above 7 indicates a basic (alkaline) solution, where the concentration of OH⁻ ions is higher.

The pH scale is defined by the equation: pH = -log [H⁺]

*Where [H⁺] is the concentration of hydronium ions

pOH:

The pOH scale measures the alkalinity or acidity of a solution based on the concentration of hydroxide ions (OH⁻).
It is also a logarithmic scale ranging from 0 to 14.
A pOH value below 7 indicates a basic (alkaline) solution, where the concentration of OH⁻ ions is higher.
A pOH value above 7 indicates an acidic solution, where the concentration of OH⁻ ions is lower.
A pOH value of 7 represents a neutral solution.

The pOH scale is defined by the equation: pOH = -log [OH⁻]

*Where [OH⁻] is the concentration of hydroxide ions

This article on pH, pOH, and the pH scale offers tons of valuable information.[/vc_column_text][/vc_column][/vc_row][vc_row el_id=”Acid-base equilibrium”][vc_column][vc_empty_space height=”45px”][vc_separator][vc_empty_space height=”45px”][ultimate_heading main_heading=”Acid-base equilibrium” main_heading_color=”#090a0f” alignment=”left”][/ultimate_heading][vc_column_text]Ka and Kb are equilibrium constants that are used to quantify the strength of acids and bases, respectively. They provide information about the extent that acids and bases will ionize in aqueous solutions.

Ka is a measure of the extent to which an acid donates protons (H⁺) in a solution. The Ka value is calculated for weak acids and represents the equilibrium constant of the acid dissociation reaction. For a generic acid, HA, the dissociation reaction can be represented as:

HA (aq) ⇌ H⁺ (aq) + A^– (aq)

The Ka expression for this reaction is written as [H⁺][A^–] / [HA], where [H⁺] represents the concentration of H⁺ ions, [A^–] represents the concentration of the conjugate base ions, and [HA] represents the concentration of the undissociated acid. The higher the Ka value, the stronger the acid, indicating a greater degree of ionization.

Kb is a measure of the extent to which a base accepts protons (H⁺) in a solution. The Kb value is calculated for weak bases and represents the equilibrium constant of the base dissociation reaction. For a generic base, B, the dissociation reaction can be represented as:

B (aq) + H₂O (l) ⇌ BH⁺ (aq) + OH^– (aq)

The Kb expression for this reaction is written as [BH⁺][OH^–] / [B], where [BH⁺] represents the concentration of the conjugate acid ions, [OH^–] represents the concentration of hydroxide ions, and [B] represents the concentration of the undissociated base. The higher the Kb value, the stronger the base, indicating a greater degree of ionization.

It’s important to note that the strength of an acid and a base are inversely related. Strong acids have a high Ka and a low pKa value (negative logarithm of Ka), while strong bases have a high Kb and a low pKb value (negative logarithm of Kb).[/vc_column_text][vc_column_text]