Chapter 12 - Acids and Bases

what is an acid?

a substance that dissociates in water to produce H⁺ ions (protons)

what is a monobasic/ monoprotic acid?

an acid that dissociates to give one H⁺ ion

e.x HNO₃ , HCl

what is a dibasic/ diprotic acid?

acids that dissociate to give 2H⁺ ions

e.x H₂SO₄

what is Arrhenius’ definition of a strong acid?

a strong acid is a substance that completely dissociates in water to give H⁺ ions

e.x HCl

what is Arrhenius’ definition of weak acids?

a substance that only slightly dissociates in water to give H⁺ ions

e.x CH₃COOH (vinegar)

what ion do H⁺ ions form when they bond with lone pairs in water molecules?

hydronium ion (H₃O⁺)

what is the term for a bond where both atoms come from the same atom?

dative / coordinate covalent bond

what type of bond does the H⁺ ion and water molecule form?

covalent bond

what is an alkali?

a base that dissolves in water

what is Arrhenius’ definition of a base?

a substance that dissociates in water to produce OH^- ions (hydroxide ion)

what is Arrhenius’ definition of a strong base?

a substance that completely dissociates in H₂O to produce OH^- ions

e.x NaOH

what is Arrhenius’ definition of a weak base?

a substance that only slightly dissociates in water to produce OH^- ions

e.x Mg(OH)_{2 ,} Ca(OH)₂

what happens when an acid dissociates in water?

H⁺ ions dissociate and bond with lone pair in water molecules to form hydronium ion (H₃O⁺)

why are basic solutions slippery?

they convert some oil in your skin to soap

what are the limitations to the Arrhenius Theory?

• bare H⁺ ions do not exist in solutions as suggested, rather forming H₃O⁺ ions

• definitions restricted to to aqueous solutions (reactions with water), removing other solvents from definitions

• not all acid-base reactions need water as suggested

  e.x NH₃ + HCl = ammonia

what is the modern theory of acids and bases?

Bronsted-Lowry Theory

what is the Bronsted-Lowry definition of an acid?

an acid is a proton donor

what is the Bronsted-Lowry definition of a base?

a base is a proton acceptor

what is an amphoteric / amphiprotic substance?

a substance that can act as either an acid or a base

e.x H₂O

according to Bronsted-Lowry, what is a strong acid?

an acid that is a good proton donor

according to Bronsted-Lowry, what is a strong base?

a base that is a good proton acceptor

compare Arrhenius Theory and the Bronsted-Lowry Theory?

Arrhenius

• limited to aqueous solutions

• limited to bases that produce OH^- ions in water (doesn’t always happen)

• doesn’t consider existence of hydronium ion

• can’t explain how substance can be amphoteric

Bronsted-Lowry

• applicable to reactions in gaseous states and water

• applicable to bases such as NH₄, where no O atoms present and is impossible to form OH^- ions

• considers existence of hydronium ion

• explains how substance can be amphoteric in terms of proton transfer

• broadens range of substances definiable as acids/ bases

  e.x NH₃ base in Bronsted-Lowry but not Arrhenius

how does an acid change into its conjugate base?

by donating a proton

how does a base change into its conjugate acid?

by accepting a proton

what are conjugate acid-base pairs?

any pairs consisting of an acid and a base that differ by one proton

what is neutralisation?

a reaction between an acid and a base where a salt and water is formed

what is a salt?

a substance formed when a hydrogen ion of an acid is replaced by a metal or an ammonium ion

e.x H⁺ in HCl is replaced by Na to form the salt NaCl

what is a medical example of neutralisation?

taking antacid medication to neutralise excess stomach acid

what is an agricultural example of neutralisation?

farmers spreading lime on fields to neutralise acidic soil so crops can grow

how does neutralisation work for wasp stings?

vinegar is used to neutralise base in wasp stings