1.9 - Acid-Base Titrations

Strong acid/base definition

fully dissociates in solution

Weak base/acid

partially dissociates in solution

Molarity definition

concentration in mol dm^-3 expressed using M

Concentration definition

number of moles/mass present in stated volume

Standard solution definition

solution for which concentration is known

Phenolphthalein acid to alkali

pink to colourless

Methylorange acid to alkali

yellow to red

What titrations is phenophthalein suitable for?

strong acid-strong base, weak acid-strong base

What titrations is methylorange suitable for?

strong acid-strong base, strong acid-weak base

Strong acid examples

HCl, H2SO4, HNO3

Weak acid examples

ethanoic acid

Strong base examples

NaOH, KOH

Weak base examples

NH4OH, Na2CO3

What is a titration?

measured volume of standard solution added to known volume of unknown concentration until reaction complete

Which solution placed in burette/pipette?

burette is standard solution, pipette is unknown

What is it called when neutralisation occurs in a titration?

endpoint

Three procedures to ensure are followed during a titration?

safety, accuracy, reliability

Safety in titration

safety filler and gloves

Accuracy in titration

rinse apparatus with solution to be used, standard solution drop wise at end, swirl flask

Reliability in titration

repeat until concordant results

Pipette and conical flask steps in titration

rinse conical flask/pipette with deionised water, fill using safety filler to calibration mark, add indicator

Burette steps in titration

rinse burette with deionised water and standard solution, clamp in retort stand, place filter funnel, charge burette with standard solution to zero, ensure no air bubbles/jet full

Carrying out titration steps

add standard solution while swirling, once colour changing add drop by drop, stop at endpoint and record, repeat at least twice until concordant results, calculate average titre ignoring rough/outliers

What does accuracy describe?

how close result is to true value

What does precision describe?

measure of spread at measured values

How is a result valid?

good degree of accuracy and small uncertainty

Uncertainty for graduated equipment

half a division of either side of smaller unit on scale

Uncertainty for volumetric equipment

precision error associated with it

Steps to prepare diluted solution

rinse pipette with water and vinegar, fill to calibration mark with safety filler, rinse 250cm3 volumetric flask with deionised water and add vinegar, add dropwise until meniscus on calibration mark