Chapter 14 - Gravimetric Analysis

Pipette

Used to find specific volume

Liquid out of this called aliquot

Conical Flask

Known volume or solution - and place it in ready for volumetric analysis

Burette

Standard solution of acid or base - in burrete

volume of liquid delivered by a burette - called titre

Titration & Standardisation

Measured concentration/volume with a solution with unknown concentration/solution

When unknown variable is calculated - standardised

Equivalence Point

The point where two chemcials react

Happens when gradient of the pH curve is the steepest

Done through stoichiometry - (theoretical)

End point

Where the indicator changes colour - during neutralization

Must be very close to equivalence point

What happens in the flask - the practical part

Indicators

Is very very strong in acidic/base medium - highly observable

Indicator’s pH range must be overlapping in equivalence range

Burette

in 0.1ml brackets

single drop = 0.5mln

Risnign galssware

Must be clean

Rempves chemocals abd gives more accurate and precise volumetric analysis

Must be rinsed with correct liquid

Burrete/pippet - rinisng

Final rinse - with acid or base that will be used

Using water will dilute the solution

Volumetric/conical flask - rinsing

Only with deionised water

Rinsing with solution will bring in unmeasured amount of solution - can affect results

Precise

Values that are very similar to one another

Accurate measurements

Average measurement - very close to accepted value

In accordance with previously determined results

Types of Errors

Mistakes - Human errors (incorrect reading, avoidable, spilling, using pipette incorrectly)

Systematic - Fault in apparatus (10ml pipette giving 10.2 ml, using unsuitable indicator)

Random Errors - Errors with no particular pattern

Volumetric Flask

Making standard solution/titre used within the titration.

Standard Solutions

Concentration of solutions that are known

Primary Standards

Pure substances to prepare known concentration solutions

Amount of substance in moles can be accurately measured from mass - primary standards

Properties Of Primary Standards

Readily availabel in pure form

Known chemical formula

Contain high molar mass to minimise errors in weighing

Inexpensive

Easy to store without deteriorating the atmosphere

Difference between standardised solution and primary standrard

Use primary standard to make the standardised solution