Titration Validation

What does anhydrous mean?

• Containing no water.-

Contrast anhydrous to hydrated

• Hydrated compounds contain water molecules.

Why is it desirable to use an anhydrous substance? (3 reasons)

• Higher in purity.

• Doesn’t allow for water to alter it’s mass.

• Mass is accurate rep. of moles.

What is an Aliquot?

• Known & accurate vol. delivered from pipette.

Describe when you would take an aliquot

• Process of standardising solution during titration when you need to measure precise vol. of of solution your analysing.

Describe how you would take an aliquot

• Use a volumetric pipette & take aliquot from primary standard to prepare secondary standard.

Why can chemicals never be returned to the storage bottle? (3 reasons)

• Contamination risks.

• Cross-contamination.

• Loss of accuracy.

Why is it vital to always pour out minimum substance needed in any situation? (3 reasons)

• Prevents waste.

• Can be costly & environmentally harmful

• Increases risk of spills, exposure, etc.

What is a primary standard?

• Highly pure, stable substance with known conc. used to accurately determine conc. of unknown solution.

What form of prior treatment does NaCO3 require before use as a primary standard?

• Drying (heating) to remove moisture & cooling in desiccator to prevent reabsorption of water.

Why should all solid be dissolved before transfer of solution from beaker to volumetric flask? (3 reasons)

• Ensures accurate conc.

• Prevents loss of solute.

• Ensure homogenous solution

Is it necessary to weigh out exactly the calculated mass?

• No as primary standard’s mass is true & accurate rep. of moles.

What are 3 key features of a primary standard?

1. Obtainable in pure form.

2. Shouldn’t alter during weighing.

3. Should have relatively high formula weight.

Why are the 3 key features important to ensure a reliable standard is produced?

1. Ensures molar conc. is accurate.

2. Ensures measurements are accurate.

3. Reduces weighing errors.

Why should a constant, minimum amount of indicator be used in titrations? (3 reasons)

• Prevents indicator from affecting pH of solution.

• Ensures clear & consistent endpoint.

• Prevents overly intense or faint colour changes.

What indicator is best for strong acid and weak base titration?

• Methyl orange as it changes colour in pH range of 3.1-4.4 & equivalence point of reaction is slightly acidic (around pH 4.5-5.5).

What should the following equipment be rinsed with and why?

What is the impact if you rinsed with DI water instead of “solution to be used”?

• Dilution errors affecting conc. of solution.

Can solution be blown out of pipette? (3 reasons)

• Pipettes are calibrated to retain small residual volume.

• Affects accuracy & precision.

• Potential contamination.

Explain the difference between the end point and equivalence point?

• Endpoint: point at which indicator changes colour visually signalling titration is nearly complete.

• Equivalence point: theoretical point in titration occurring when exactly enough titrant has been added to completely neutralise acid or base.