Acids and Bases Flashcards
what the fuck does the motherfucking, you know, fucken Brønsted-Lowry theory do (prolly fucken jack shit but whatever)
explains the acid-base behaviour in terms of a proton transfer reaction where bases are proton-acceptors aand acids are proton-donors
what notion does this intorduce
that acid-base behaviour is relative and circumstantial, thus some substances are amphiprotic/amphoteric (can act as base or acid) depending on species they are interacting with.
what kind of reactions are all Brønsted-Lowry reactions
reversible reactions, acknowledge that a substance can’t act as acid without another substance acting as a base.
what happens when an acid loses a proton in a proton transfer reaction
it forms what is know as a conjugate base, while the base accepting a proton forms a conjugate acid. conjugate acid-base pair differ on ly by one proton.
what does the arrhenius theory of acids and bases state
acids ionise in solutions to produce hydrogen ions while bases dissociate in solution to produce hydroxide ions.
why is Arrhenius theory limited
it only applies to acid-base behaviour in aqueous solution (solvent is needed), and also doesn’t predict the basic nature of carbonates, oxides and salts that don’t contain hydroxide
what are monoprotic acids
(note acids can be classified as being monoprotic or polyprotic) they can dnate a single proton per acid molecule in a transfer reaction,
what are polyprotic acids
can donate more than one proton per acid molecule
what is a conjugate base
A conjugate acid is formed when a proton is added to a base, and a conjugate base is formed when a proton is removed from an acid
why is coniugate base of polyprotic acid different
usually is less acidic than the orginal acid ( as shown bny their individual acid constants) this is explained as the acid becomes less likely to donate positive charge (H+) as molecule becomes increasingly negative, so it becomes less.
how is the strength of an acid determined
by the extent to which it ionises (via proton donation).
what is the acid dissociation constant (Ka)
as proton-transfer reactions are technqically equilibrium processs, a constant can be assigned to every reaction to quantify the extent to which the reaction proceeds, which can aid in measuring acid strength
write the acid dissociation constant (Ka)
seek page 9
what if Ka is large (>1)
then the aiced can considered strong as it ionises to a large extent
what if Ka is small (<1)
then acid can be considered weak, as few acid molecules ionise (most remain in their molecular form)
what should be kept in mind when using the acid dissociation constant (Ka)
water has a fixed concentration and as such is not included in the expression
and the strong the stronger acid is, weaker its conjugate base, as conjugate base is less likely to accept a proton because acid resits reformation.
what is the conjugate base of a weak acid known as
a strong base, sicne acid mostly remains in molecular form, hence conjugate base is more likely to accept a proton to reform the acid molecule.
what is salt
an ionic compound that is formed in the reaction between an acid and base
how can salt be classified
acidic, basic, or netural, based on way in which anin and/or cantion interacts with water since ionic compounds undergo hydrolysis reactions
when salt classified as acidic
if anion/cation produces hydronium ions when reacting water, the compound is classed as acidic, as it produces a acidic solution
when salt classified as neutral
if anion/cation produces hydroxide ions when reacting water, the compound is classed as basic, as it produces a basic solution
when salt classified as basic
sometimes a salt has both acidic and basic ions, in this case it can be neutral or the “stronger” ion determines its properties. the properties of the salt can affect the properties of the entire solution.
what are buffers
solutions that resist change in pH (within a certain range) when they have acids or bases added to them.
what kind of pair are buffers generally
generally a weak acid-base conjugate pair this works becasue the pair can exist together in a solution without neutralising each other, but still neutralise any added acid or base
what does le chateliers principle do
as the buffer system operates under a reversible equilibiurm reaction, the bahaviour of the system can be predicted by this
what happens when acid or base is added to the buffer
equilibrium shifts t favour the reaction that consumes the added acid or base.
what does the addition of an acid or a base do to a system
the addition of acid or base to system can also neutralise one of the conjugate pair species in which base equilibrium shifts to favour the reaction that produces more of this species, in both instances changes to pH are minimal.
what is the buffer capacity
amount of acid or base that can be added to buffer system without significant change to pH
higher buffer capacities
solution should have high concentratins of the acid-base conjugate pair, and similar concentreations or the two species making up the conjugate pair.
explain waters self-ionisation
despite waters covalent molecular strucutre, it can do this, where 2 water molecules form hydronium and hydroxide ins via a proton transfer reaction.
explain the autoionisation constant (Kw)
this reversbile equilibrium reaction favours formation of water molecules and hydronium and hydroxide ions have extremely small concentrations of 1.0 x 10^-7 mol^-1 at 25 C. As this reaction is in a state of equilibrium, it can be assineed the autoionisation constant (Kw)
when is water neutral
if the concentration of hydrogen and hydroxide ions are equal than the water is said to be neutral.
explain the 1.0 x 10^-7 expression of concentrations of hydronium and hydroxide ions in water.
in neutral water the concentraiton of hydronium ions and hydroxide ions is 1.0 x 10^-7. this expression shows that concentrations of hydrogen ions and hydroxide ions are inversely related.
explain how the autoionisation constant varies with different temperature.
since its an endothermic process, increase in temp. favours formation of the products, hence increasing the concentration of hydronium and hydroxide ions in solution.
what makes a solution neutral
not one that has a pH of 7, important to remember this. for a solution to be neutral, it must have equal concentrations of hydroxide and hydronium.
what is a solutions acidity based on
hydrogen ion concentration, this can be used to determine pH as pH is a logarithmic function of hydrogen ion concentration.
pH = - log_10[H+]
what are indicators
they’re weak conjugate acid-base pairs used in acid-base reactions because their colour is pH dependant.they work using le chateliers principle cause they produce an equilibrium system in which the weak acid/base is a different colour to conjugate base/acid.
what does the addition of a base or an acid do to the concentrations of the conjugate pair
addition of acid or base changes the concentrations of the conjugate pair relative to one another, which cause the solution to change colour.
what are titrations
a form of quantitative analysis, an analytical procedure involving an acid-base reaction
what is the point of titrations
to determine the concentration of a particular solution by reacting it (acid/base) with a solution of accurately know concentration.
what is a standard solution
this is the solution of accurately known concentration
what is a ‘unknown’ solution
this is the solution whose concentration you are trying to determine
what is the equivalence point in a titration
is the point at which the species involved in the reaction exist in the stoichiometric ratios indicated in the balanced chemical equation for the reaction. (Where all the acid/base in the aliquot has been neutralised”
what is the end point
this cannot be seen with the naked eye, but the point at which the indicator in the solution changes colour, this is a close approximation of equivalence
what is a titration curve
equivalence can be noted a titration curve as the point at which pH changes rapidly (point of inflection).
what are primary standards done?
accurately measured and mixed with distilled water to an exact volume to form a primary standard, which is accurately known concentration - the standard solution.
what must a primary standard be ?
be available in pure form
be stable (not react with the atmosphere)
have a relatively high molar mass
be soluble in a suitable solvent
what is a primary standard
typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained
what are the specialised glassware
conical flask
burette
pipette
volumetric flask
explain how to prepare a conical flask
pre-rinsed with distilled water; contains an aliquot (carefully measured volume of either the standard solution, or the ‘unknown’ solution)
explain how to prepare a burette
pre-rinsed with reagent to be placed in it; dispenses a variable volume of either the standard solution, or the ‘unknown’ solution int the conical flask, where it the acid-base reaction take place
explain how to prepare a pipette
pre-rinsed with reagent to be placed in it; dispenses the aliquot into hte conical flask
explain how to prepare a volumetric flask
pre-rinsed with distilled water; use to prepare the standard solution to an exact known concentration.
what is an acid
A chemical that gives off hydrogen ions in water and forms salts by combining with certain metals.
what is a base
A base is a substance that can neutralise the acid by reacting with hydrogen ions. Most bases are minerals that react with acids to form water and salts.
