Lab 5: Acid-base equilibrium: capacity of buffers

what are we doing today

make buffer solutions of a desired pH and also test how these solutions react to the addition of a strong acid and a strong base

the capacity of a buffer solution depends on what

pH and the absolute concentrations of the conjugate acid-base pair

the strength of an acid or base is characterized by what

degree to which it will dissociate when placed into water

if its a weak acid/base will undissociated species remain along with dissociated ones

yes

in an equation of a strong acid/base dissociating, does the equilibrium lie to the left or right

strongly to right (--> instead of <-->)

how do you calculate Ka

[H3O+][A-]/[HA]

the greater the value of Ka, the greater or less the degree of dissociation

greater

what can the henderson hasselbalch equation be used for

can be used to estimate the pH of buffer solutions

formula for hasselbalch equation

pKa + log[A-]/[HA]

the equation is only valid within +/- ____ pH unit of the pKa acid

1

buffer solutions contain what

weak acid and its conjugate base
weak base and its conjugate acid

when small amounts of acid or base are added to a buffer solution, the buffer solution is able to what

resist changes in pH

what is the capacity of the buffer solution

the limit of how much strong acid or base that you can add before the buffer "breaks"

the capacity of the buffer depends on both the ______________ and ___________________

ratio of the concentrations of the conjugate acid-base pair and also on the total absolute concentrations of the conjugate acid base pair

when making a buffer solution, you must consider both the ________ and ________ of the desired buffer solution

pH, capacity

1st step in this experiment

prepare the solution using a known value and molar concentration of a weak acid. Add an appropriate number of moles of the conjugate base to achieve the correct ratio of [A-]/[HA]. You will add aqueous sodium acetate to aqueous acetic acid

2nd step

prepare the solution using a known value and molar concentration of the weak acid and add an appropriate amount of a strong base to achieve the correct ratio, The strong base will convert some of the weak acid to the conjure base. Adding sodium hydroxide to acetic acid

all acid base buffer and titration calculations start as what

limiting reactant problems

to prepare a buffer solution by the reaction of a weak base with a strong acid, which reactant must be limiting

strong acid

the pH censor is an example of what

galvanic cell (whose output is proportional to the difference between the concentration of hydrogen ions in the test solution and the concentration of of hydrogen ions that are contained in a reference cell located in the body of the sensor

buffering capacity can be represented by what

change in volume added / change in pH of solution

the more volume required to change the pH of the solution, the higher the

capacity of the buffer

how should we wipe of pH electrode

blot, excess pressure can damage the tip

the goal is to measure in incremements of what

0.2 [H units

what are we titrating with

NaOH and HCl