buffers

what are buffer solutions?

they are solutions that are able to resist a change in pH when small amounts of acid or base are added

what does a buffer consist of?

a weak conjugate acid base pair and one of its salts. Meaning weak acid and its conjugate conjugate base or a weak base and its conjugate acid

what is the difference between and acid and its conjugate base?

a acid donates hydrogen ions (protons) to a base to a limited extent. The acids conjugate base contains one less hydrogen ion (proton) than the acid.

what is the difference between a base and its conjugate acid?

the base contains one more hydrogen ion (proton) from acids to a limited extent. The bases conjugate acid contains one more hydrogen ion (proton) than the base.

what is the buffer for the ethanoic acid?

ethanoic acid and sodium ethanoate solution. this will produce a buffer that is at a pH of 4.76

for a buffer to work what must the concentrations of the weak acid/ base and one of its salts be?

in equal molar concentrations

How would you be able to change the pH of a buffer solution?

you would need to change the ratio of acid/ base to salt. therefore equilibrium will shift and the concentrations of H+ ions will also shift

how is a ethanoic acid/ sodium ethanoate buffer prepared?

it is prepared by dissolving approximately equal molar amounts of ethanoic acid and sodium ethonate (NaCH3OO) in water. Yje sodium ethanoate will dissociate completely in water, producing Na+ ions and CH3COO- ions

what happens to ethanoic acid molecules when they are dissolved in water?

a small proportion of CH3COOH molecules will ionise to form CH3COO- and H30+ ions. however the vast majority will stay CH3COOH molecules

what are sodium ions in the CH3COOH/ CH3COO- buffer?

spectator ions, therefore they are not involved in the equilibrium reaction

CH3COO- is CH3COOH’s what?

conjugate base, as it will readily accept protons (hydrogen ions)

what is an example of a weak base buffer?

the NH3/ NH4+ buffer, when equal concentrations are mixed this buffer will have a pH at 9.25

how can you prepare a NH3/ NH4+ buffer?

to dissolve approximately equal molar amounts of ammonia solution and an ammonium salt such as ammonium chloride (NH4Cl) in water

what happens to ammonium chloride in water?

it dissociates completely, producing ammonium ions and chloride ions

what happens to some ammonia molecules when put into water?

a small proportion of ammonia molecules will ionise and produce ammonium ions NH4+ and OH- ions

what does the Ka number mean?

this is the equilibrium constant of the buffer solution

how do you work out the value of K?

the concentration of the products over the reactants

what happens when you add an acid to a buffer?

the pH may decrease to a small extent but not as much if the buffer was not present. For example, if you add HCl to a buffer solution, the extra H3O+ ions will disturb the existing equilibrium of the buffer solution. LCP tells you that the system will respond to pose this change and restore equilibrium. Therfore some of the H3O+ ions will react with a product to produce more of the reactants and decrease the H3O+ concentration in the solution

what happens when you add a base to a buffer?

the OH- ions from the base will react with the e.g reactant molecules in the buffer and this will generate more products while the OH- ions are consumed. therefore the overall change in pH is very small

what is buffer capacity?

is a measure of the effectiveness of a buffer solution at resisting a change in pH when wither a strong acid or base is added.
(this determines how much an acid or base can be neutralised before the PH changes)

what influences the effective the buffer will be in resisting changes to the pH?

the concentrations of the buffer of the weak acid and its conjugate base

when is a buffer most effective, i.e buffer capacity is greatest when?

there is a high concentration of the weak acid and its conjugate base and when the concentrations of the acid and its conjugate bases are equal.

when is a buffer system no longer effective?

when the additional OH- or H3O+ ions will no longer be removed by the weak acid or base ions. At this point there will be a sharp decrease or increase in the pH

in a buffer solution that has a higher concentration of acid can react with a greater amount of acid or base?

base.

what range should the concentrations of the weak acid and its conjugate base be?

10:1 and 1:10