From 7016e737ffbae10ea1b1c8ee5b9d482bc45c2d60 Mon Sep 17 00:00:00 2001 From: eggy Date: Wed, 5 Jan 2022 21:56:23 -0500 Subject: [PATCH] chem: Add strong/weak acids/bases, properties of acids/bases, Louis theory --- docs/sch4uz.md | 73 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 70 insertions(+), 3 deletions(-) diff --git a/docs/sch4uz.md b/docs/sch4uz.md index ac1a0d3..57e9e8d 100644 --- a/docs/sch4uz.md +++ b/docs/sch4uz.md @@ -577,6 +577,30 @@ $\Delta G = -RT\ln K_c$ ## Acids and bases +!!! definition + - An **amphiprotic** acid/base is one that can **either accept or donate** $\ce{H+}$ depending on the situation. + - A **monoprotic** acid/base is one that can only accept/ionise one $\ce{H+}$ ion. + - An **amphoteric** chemical may act as an acid or base depending on the situation. + - An **alkali/alkaline** solution is an aqueous solution of a base, which may **not** necessarily be a **basic solution**. + +An **acid** and **base** are any two corrosive chemicals that react to form water and a salt. They also dissociate/ionise (depending on theory) in water to form electrolytes that conduct electricity. + +Acids: + + - taste sour + - have a pH less than 7 in aqueous solutions at 25°C + - stain litmus paper **red** + - react with active metals to produce $\ce{H2_{(g)}}$ based on the activity series + - react with carbonates to form $\ce{CO2 + H2O}$ + +Bases: + + - taste bitter + - have a pH greater than 7 in aqueous solutions at 25°C + - feel slippery as they react with fats/oils to form soap + - stain litmus paper **blue** + - react with ammonium salts to product $\ce{NH3 + H2O}$ + ### Arrhenius theory An acid **dissociates** in water to produce $\ce{H+}$ ions (protons). @@ -585,19 +609,28 @@ A base **dissociates** in water to produce $\ce{OH-}$ ions. ### Bronsted-Lowry theory -The Bronsted-Lowry theory focuses on reactions with water and less the acid and base ions themselves. +The Bronsted-Lowry theory focuses on reactions with water and less the acid and base ions themselves, so they **ionise** instead of **dissociate**. -An acid is any compound that can **donate a proton ($\ce{H+}$) to water** to form a hydronium ion. +An acid is any compound that can **donate/ionise a proton ($\ce{H+}$) to water** to form a hydronium ion. $$\ce{acid + H2O -> acid- + H3O+}$$ !!! info In practice, the acid must contain a hydrogen atom attached by an easy-to-break bond (usually $\ce{H-O}$), but any high electronegativity difference polar bond would work as well. -A base is any compound capable of **removing a proton ($\ce{H+}$) from an acid**. +A base is any compound capable of **accepting/removing a proton ($\ce{H+}$) from an acid**. $$\ce{acid + base -> acid- + base+}$$ !!! info The proton usually comes from water. The base must be able to accept an $\ce{H+}$ ion to form a **dative covalent bond**, so they must contain **lone pairs**. + +Polyprotic acids ionise their $\ce{H+}$s one by one **sequentially**. + +!!! example + $\ce{ + H3PO4 + H2O <=> H2PO4- + H3O+ \\ + H2PO4- + H2O <=> HPO4^2- + H3O+ \\ + HPO4^2- + H2O <=> PO4^3- + H3O+ + }$ #### Conjugate acids/bases @@ -613,8 +646,42 @@ The result of an acid losing a proton is a **conjugate base**. ### Louis theory +A Lewis **acid** is any species that **accepts** an electron pair to form a dative covalent bond. + +A Lewis **base** is any species that **donates** an electron pair to form a dative covalent bond. + ### Strong/weak acids/bases +**Strong** acids/bases will **completely** dissociate/ionise in an aqueous solution. This means that the initial concentration of acid will be equal to the end concentration of $\ce{H+ or H3O+}$. + +All strong polyprotic acids initially have a one-way reaction then follow with equilibrium reactions. + +!!! warning + Strength is a property of an acid and has nothing to do with its concentration. + +**Weak** acids/bases will only **partially** dissociate/ionise in an aqueous solution, leaving behind most of the initial acid ($\ce{[acid] > [H+]}$ at equilibrium). + +!!! warning + Measuring pH only returns $\ce{[H+] or [H3O+]}$, so it cannot be used to determine the concentration, identity, or strength of an acid. + +All weak polyprotic acid reactions are equilibrium reactions. + +!!! example + The following is a list of strong and weak acids: + + | Strong acid | Weak acid | Strong base | Weak base | + | --- | --- | --- | --- | + | $\ce{HClO4}$ | any $\ce{COOH}$ | $\ce{LiOH}$ | $\ce{NH3}$ | + | $\ce{HCl}$ | $\ce{CO2}$ | any $\ce{group\ 1 + OH}$ | $\ce{Al(OH)3}$ | + | $\ce{HBr}$ | $\ce{SO2}$ | any $\ce{group\ 2 + (OH)2}$ | | + | $\ce{HI}$ | $\ce{HF}$ | | | + | $\ce{H2SO4}$ | $\ce{HCN}$ | | | + | $\ce{HNO3}$ | $\ce{H3PO4}$ | | | + +To experimentally distinguish between a strong or weak acid/base, if their concentrations are equal, total **ion** concentration or $\ce{H3O+}$ concentration can be compared since the stronger acid ionises more. + +Practically, this means comparing the rate of reaction with a metal or water or measuring conductivity as they reflect total ion count. + ### pH and pOH ## Organic chemistry