acids and bases Flashcards
Arrhenius theory
acids ionise and form hydrogen ions,
bases dissociate in water to form hydroxide ions
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
Acids are
Bases are
proton donors
proton acceptors
An acid-base reaction involves
an exchange of protons from an acid to a base
HCl added to water
water/HCl acted as
it breaks apart to form hydronium ion and chlorine ion.
HCl acted as an acid bc has donated hydrogen ion to eater. Water acted as a base bc accepted a proton from HCl
HCl hydrolysis reaction
HCL dissociation reaction
HCl(g)+H2O(l)–> H3O+(aq) +Cl-(aq)
HCl(g)+H2O(l)–> H+(aq) +Cl-(aq)
Hydrolysis reaction
occurs when a molecule/ion in an aqueous solution reacts with water either by accepting or donating a proton
Advantages of BL theory
acids and bases not restricted to aqueous solutions
Limitations of BL theory
cannot be applied to run b/w acidic and basic oxides
under certain conditions solid calcium oxide (basic oxide) reacts with gaseous CO2 (acidic oxide) to produce salt calcium carbonate
CaO(s) +CO2(g)–> CaCO3(s)
Conjugate acid-base pairs
are 2 species that differ by a proton
Conjugate acid of a base
contains 1 more H+ ion (proton) than the base
Conjugate base of an acid
contains 1 less H+ ion (proton) than the acid
HCl(g)+H2O(l)–> H3O+(aq) +Cl-(aq)
Acid/base/conj?
(((HCl(g)+H2O(l)–> H+(aq) +Cl-(aq)))
HCl acid
Cl- acids conj base
water base
H3O+ bases conj acid
Amphiprotic
substances that can behave as either an acid or a base (water)
Amphiprotic substances Examples
H2O, H2PO4-, HSO4-, CO3^2-, HCO3-,HPO4^2-, H2SO4
Monoprotic acid
donate 1 proton per molecule
ethanoic acid
acidic proton
the hydrogen atom that is donated by and acid
polyphonic acid
diprotic
triprotic
can donate more than 1 proton per molecule(in steps)
can donate 2 protons
3 protons
Strong acid (def)
will readily donate a proton (ionise)
donate protons easily
solution of strong acid contains ions with virtually no unreacted acid molecules present
Weak acid
Only ionises partially ethnic acid (CH3COOH), carbonic acid (H2CO3), phosphoric acid (H3PO4)
Strong acid examples
hydrochloric acid (HCl), sulphuric acid(H2SO4), Nitric acid(HNO3)
Strong bases
accept protons easilt sodium hydroxide (naOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2)
Weak bases
only accept a small portion of protons
ammonia (NH3)
Acidity constant (Ka)
the equilibrium constant for a hydrolysis reaction of an acid
Ka= [H3O+][CH3COO-]/[CH3COOH]
water not included
Basicity constant (Kb)
symbol given to eq constant for a hydrolysis rxn of a base
more???
Concentrated and dilute
describe the amount of acid or base dissolved in a given V of solution
what do Ka indicate
the strength of an acid
Pure water undergoes
self ionisation (to a small extent) H2O(l)+H2O(l) H3O+(aq)+ OH(aq)-
Ionic product (ionisation constant) of water
Kw=[H3O+][OH-]=1.00 x 10^-14 @25ºC
pH
a scale that is a way of expressing the levels of acidity
pH=-log10[H3O+]
[H3O+]=
[H3O+]= 10^-pH
Kw and temperature
T will affect value of Kw.
As Temp increases so does the value of Kw which lowers pH
This is bc self ionisation of water is endothermic
dilution
mixing concentrated acid with water
Salts
are ionic compounds containing a positive ion (cation) other than a hydrogen ion (H+) or a negative ion(anion) other than oxide ion (O^2-) or (OH-)
Salts formed from?
neutralisation rxn by combination of acid and base
has cation from base and anion from acid
A dissociation reaction (salts) takes place
when salt dissolves in water
The cation/anion produced may react with water to produce either H3O+ or OH- ions
Neutral salts
salts produced in reaction between strong acid and strong base
the anion and cation do not react with water
Salts of strong acid and weak base
are acidic bc the conj acid of weak base hydrolyses to form hydronium ions
Acidic salt
a salt produced in rxn between strong acid and weak base
the anion/cation of acidic salt reacts with water by donating proton
Salts of weak acid and strong base
are basic salts bc anions hydrolyse to form hydroxide ions
basic salt
a salt produced in rxn b/w weak acid and strong base
anion/cation of basic salt reacts with by accepting proton
salt of weak acid and weak base
involves 2 competing hydrolysis reactions
The conj base of weak acid reacts w/ water to form H3O+
The conj acid of weak base reacts w/ water to form OH-
The pH of a solution of a salt of a weak acid and weak base
depends on the extent to which each rxn occurs
Acid and base properties of common ions
Neutral (from strong acids+bases)= Cl- Br- NO3-
Acidic (from weak bases)= NH4+,HSO4-, H2PO4-
Basic(from weak acids)= CO3^2-, HPO4^2-, HCO3-, PO4^3-, SO4^2-, F-
Determine acidity of salt produced by rxn of NaOH and phosphoric acid
NaOH+ H3PO4–> ect
PO4^3- basic ion so salt is basic
Aqueous solutions of salts of polyprotic acid
can be neutral acidic or basic
