Lecture 5: Titrations

What is the definition of a titration?

A method to determine the amount of reagent w/ known [ ] to fully react w/ an analyte

What are the 6 types of titrations and what are their measured quantities?

volumetric titration: volume of reagent

gravimetric titration: mass of reagent

coulometric titration: quantity of charge that completes rxn

redox: volumetric method where rxn involves electron transfer

amperometric and spectrophotometric

What is a back-titration?

process by which excess of a standard solution used to complete 1st reaction w/ analyte is determined by titration w/ a second standard solution

When are back-titrations often required?

when rxn rate is slow or standard solutions lacks stability

What are the definitions of equivalence point and end point in a titration?

equivalence point: when amount of reagent = amount of analyte

end point: chemical equivalence → physical change

What is the definition/equation for titration error?

diff in volume/mass b/w equivalence point and end point

Et=Vep-Veq

What is a primary standard?

highly purified compound serving as reference material

What are the 6 criteria of a primary standard?

1. high purity

2. atmospheric stability

3. absence of hydrate water

4. modest cost

5. reasonable solubility in titration medium

6. reasonably large molar mass

Are primary standards often used?

No b/c very few compounds reach the criteria, so secondary standards are often used

What are the 4 criteria for an ideal standard solution?

1. be sufficiently stable

2. react rapidly w/ analyte

3. react ~ completely w/ analyte

4. undergo selective rxn w/ analyte

What are the 2 methods used to establish the [ ] of standard solutions?

1. direct method: mass of primary standard dissolved & diluted to a known volume and [ ]

2. standardization: titrating the standard against a primary or secondary standard

In standardization, the titrant to be standardized will be used to titrate what 3 options?

1. known mass of a primary standard

2. known mass of a secondary standard

3. measured volume of another standard solution

What is the difference between molar [ ] and normal [ ] of a standard solution?

molar: # of moles in 1 L solution

normal: # of equivalents in 1 L solution