acid and base Flashcards
what are the general characteristics of an acid
they have a sour taste, they’re liquid and react with bases
what are the general characteristics of a base
they have a bitter taste, they’re solid, react with acids and they feel soapy
what did Arrhenius model 1884 suggest about acids and bases
suggested that when acids dissolve in water they release H+ ions and that when bases dissolve in water they release OH- ions
what happens when an acid (eg, HCl) goes into water
it dissociates and forms H+ and Cl- ions
what happens when a base (eg, KOH) is added into water
it dissociates and forms K+ and OH- ions
what does aqueous mean
can dissolve in water
what does dissociation mean
when a chemical reaction occurs and the compound breaks into 2 or more substances. (eg, AB= A + B)
what is a neutralisation reaction
when we mix an acid and a base
(eg, HCl + NaOH = H20 + NaCl)
what are the limitations of the Arrhenius model
- ## is it an acid or base eg, NH3 can act as both
what model can be used instead of the Arrhenius model
the Bronsted-Lowry model (1923)
what does the Bronsted-Lowry model suggest
suggests that an acid can donate a proton H+ and a base can accept a proton H+
what does acidity and basicity depend on and not depend on
- depends on chemical species and not substance
- depends on chemical reaction and not chemical formula
describe an acid
an acid can be strong or weak. it can form aqueous solutions with a pH of less than 7. they can ionise meaning they can form ions such as H+
what does pH mean
the conc of H+ ions
describe strong acids
they release lots of H+ ions meaning the ionise (convert into ion) and dissociates (splits into 2 molecules) completely
describe weak acids
they don’t ionise meaning only some H+ ions are released and dissociate completely (only some)
why do weak acids have a forward and backwards arrow in the reactions
because reactants can form products and products can reform reactants. they reach an equilibrium as they don’t completely dissociate.
what does strength mean
this means how much an acid dissociates
what does concentration mean
how much acid there is in a certain volume. the more concentrated a substance is the more acid it contains.
what is the equation to calculate the pH (of an acid)
pH= -log [H+]
what is the equation to calculate the pOH (of a a base)
pOH= -log [OH-]
if your pH is high what does it suggest
that you have lots of H+ ions
if your pH is low what does it suggest
that you have little H+ ions
if your pOH is high what does it suggest
that we have lots of OH- ions
if you have a low pOH what does it suggest
that there’s little OH- ions
what affect does temperature have on pH
different temperatures can cause different pH. eg, a temperature of 25 degrees gives a pH + pOH of 14.
what are the equilibrium constants for acids and bases
pKa (acids) and pKb (bases)
what is Ka
this is the acid dissociation constant (how much an acid dissociates into ions)
what is Kb
base dissociation constant (how much a base dissociates into ions)
what does pKa mean
how strong or weak an acid is, the lower the pKa the stronger the acid is and more likely to donate a proton (H+)
what does pKb mean
how strong or weak a base is, the lower the pKb is the stronger the base is.
if an acid releases lots of H+ ions what does this mean about the pH
the pH is low (strong acid)
if an acid has a high Ka what does this mean about the pKa
pKa is low which means strong acid
if there’s lots of OH- ions what does it mean about the pOH
the pOH will be low which means high basicity of alkalinity
if the Kb is high what does it mean about the pKb
means it’s a strong base as base dissociation constant is high (lots of OH- ions)
in a equation do the products go on top or bottom
on the top
in an equation where do the reagents go
on the bottom
what does a small Ka mean
weak acid
what does a large Ka mean
strong acid
what does a small pKa mean
strong acid
what does a large pKa mean
weak acid
what is the equation to calculate Ka
Ka= [H+] [A-]/ [HA]
what is the equation to calculate pH
[A-]
pH= pKa + log —-
[HA]
what is a buffer
is a solution that can resist a change in pH after an acid of base is added
