Topic 8 - Acids and bases - Theories, properties, and the pH scale

Sep 22, 2026

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Topic 8 covers acids and bases, starting with the Brønsted-Lowry theory that defines acids as proton (H+) donors and bases as proton (H+) acceptors. It explains amphiprotic species and conjugate acid-base pairs, including how to deduce conjugates and label pairs in reactions. The topic then summarizes neutralization reactions, including salt formation with water, exothermic behavior, and how to derive salt formulas for hydroxyl, carbonate, and metal-related base reactions. Finally, it introduces the pH scale, the relationships between pH, [H+], pOH, and Kw, and the self-ionization equilibrium of water.

LanguageEnglish

CategoryExam

FormatDOCX

Pages9

Reading Time23 min

AccessFree to download

8.1 Theories of acids and bases

Brønsted-Lowry acids and bases

Amphiprotic species and conjugate pairs

8.2 Properties of acids and bases

Neutralization reactions

Types of bases and salt formation

8.3 The pH scale

pH equations and interpretation

Kw, pH/pOH relationships, and water self-ionization

Topic 8: Acids and bases 8.1 Theories of acids and bases 8.1.1 A Brønsted-Lowry acid is a proton/H+ donor and a Brønsted-Lowry base is a proton/H+ acceptor 8.1.2 Amphiprotic species can act as both Brønsted-Lowry acids and bases 8.1.3 A pair of species differing by a single proton is called a conjugate acid-base pair 8.1.4 Deduction of the Brønsted-Lowry acid and base in a chemical reaction 8.1.5 Deduction of the conjugate acid or conjugate base in a chemical reaction Brønsted-Lowry theory According to the Brønsted-Lowry theory, a substance behaves as an acid when it donates a proton to a base. A substance behaves as a base when it accepts a proton from an acid. Thus: A Brønsted-Lowry acid is a proton (H+) donor A Brønsted-Lowry base is a proton (H+) acceptor Acids can be a combination of hydrogen ions (𝑯+) and an anion. Examples include: 𝐻𝐶𝑙, 𝐻𝑁𝑂3, 𝐻𝐶2𝐻3𝑂2 Bases can be a combination of hydroxide ions (𝑶𝑯−) and metal cations. Examples include: 𝑁𝑎𝑂𝐻, 𝐾𝑂𝐻 However, sometimes a hydrogen next to a metal signifies a base such as 𝑁𝑎𝐻 Acid-Base Conjugate Pairs: A conjugate pair is two species which differ by a single proton: The acid will become the conjugate base The base will become the conjugate acid Conjugate-Base Pair Question: Label the conjugate acid-base pairs in the following reactions: CH3COOH+H2Og⇌CH3𝐶𝑂𝑂−+H3O+ Conjugate pair 1: CH3COOH/CH3𝐶𝑂𝑂− 𝐶𝐻3𝐶𝑂𝑂𝐻 is the acid because it donates a H+, so CH3𝐶𝑂𝑂− is conjugate base Conjugate pair 2: H2O/H3O+ H2O is the base because it accepts a H+, so H3O+ is the conjugate acid To find the conjugate acid of a species, add one H+ To find the conjugate base of a species, takeaway one H+ Before the Brønsted-Lory theory acids and bases were distinguished by their taste, acids tasted sour Amphiprotic Some substances can behave as either acids and bases, depending on what they react with, and can therefore donate or receive protons. Such substances are said to be amphiprotic Amphiprotic: A chemical species capable of accepting and donating protons, thus able to act as a Brønsted-Lowry acid and a base This means the species must be able to accept or donate a proton to another species H2O is amphiprotic as it is able to donate a proton to form a OH− or accept a proton to form H3O+ therefore acting as a Brønsted-Lowry acid or base Amphiprotic Species Question: Write an equation to show hydrogen phosphate acting as and an acid and a base in water Acting like an Acid: HPO42−+H2Og⇌PO43−+H3O+ Acting like a Base: HPO42−+H2Og⇌HPO4−+OH− Amphoteric Amphoteric: A species that can act as an acid or base, including reactions that do not involve a proton Amphiprotic specifically relates to the Brønsted-Lowry acid-base theory, where the emphasis is on the transfer of a proton. Amphoteric is a more general term that isn’t just confined to proton transfer All amphiprotic species are also amphoteric but not all amphoteric species are amphiprotic 8.2 Properties of acids and bases 8.2.1 Most acids have observable characteristic chemical reactions with reactivate metals, metal oxides, metal hydroxides, hydrogen carbonates and carbonates 8.2.2 Salt and water are produced in exothermic neutralization reactions 8.2.3 Balancing chemical equations for the reaction of acids 8.2.4 Identification of the acid and base needed to make different salts Neutralization Reactions Neutralization: A chemical reaction where a base and an acid react to form a salt and water Salt: An ionic Compound Acid base reactions will always produce a salt and water Salt and water are neither acidic nor basic. They are called neutral solutions Neutralization reactions are exothermic as heat is released There are different types of bases that acids react with to form salt: Hydroxyl Base: Equation: 𝐴𝑐𝑖𝑑+𝐵𝑎𝑠𝑒→𝑆𝑎𝑙𝑡+𝑊𝑎𝑡𝑒𝑟 To find the salt formula, take away the hydrogen from the acid and the hydroxyl group from the b

FAQs

What are Brønsted-Lowry acids and bases?

A Brønsted-Lowry acid donates a proton (H+), while a Brønsted-Lowry base accepts a proton (H+).

What is a conjugate acid-base pair and how do you find conjugates?

A conjugate pair consists of two species that differ by a single proton. The acid becomes the conjugate base, and the base becomes the conjugate acid; add one H+ to find the conjugate acid and remove one H+ to find the conjugate base.

How does the pH scale relate to hydrogen ion concentration?

pH is defined as pH = −log[H+], so [H+] = 10^(−pH). Changing pH by 1 unit corresponds to a 10-fold change in hydrogen ion concentration.

Sep 22, 2026

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