pag 1 make up a volumetric solution and carry out titration

What is the method of making a volumetric flask

• weigh dry weighing bottle containing solid on a balance

• Remove and pour contents into a beaker + reweigh bottle

• Record difference in mass (‘weighing by difference’)

• Add distille water + stir with glass rod until solid dissolved

• Transfer to volumetric flask with all washings

• Make up to 250cm3 mark with distilled water

• Stopper and invert

What are accuracy points to check out for with the method

What could be wrong is substance doesn’t fully dissolve and what could u do instead?

What should u use when filling volumetric flask

• making sure all substance has been transferred (It’s the reason for weighing by difference)

• If substance don’t dissolve - could be the water is too cold and the beaker should be heated gently until dissolved

• WashInes - beaker + glass rod + funnel

• Use dropping pippette for last drops to not overshoot graduated mark

What are 4 possible errors

How should u fix these

What liquid is really hard to read for miniscus

Making sure anhydrous NaHs04 isn’t too old (it could contain water)

The balanc could give a fixed uncertainty - could increase % error if weighing a small amount of solid (this is due to the balance usually measuring to 0.01g which couldn’t measure really small units - systematic error )

Transfer errors- weighing by difference method should be used to prevent residue left

And washings should be done

Miniscus misalignment - incorrectly reading graduation line - dark liquids like potassium manganite - harder to read

How would u do reduce uncertainties

Use a more accurate balance or larger mass to reduce uncertainty n weighing a solid (Reduces the systematic error)

Weighing by difference - ensures a more accurate measurement of mass added

What is the method for titration

• fill burette with solution of known conc (alkali)

• Pour 100cm³ of solution with unknown conc into second beaker (acid)

• Using pippete filler and Pipette transfer 25cm³ of this into 250cm³ flask

• Add 3 drops of indicator

• Record initial burette reading

• Titrate the acid

• Record volume in burette when colour change occurs

• Record titre volume (average from at least 2 concordant results)

What are accuracy issues with titration>

Rinse burette with alkali

Make sure area under tap contains solution as burette scale includes this volume - (Otherwise the volume needed would be higher)

Rinse 25cm³ pipettes with solution of unknown conc - the conical flask should be rinsed with distilled water

If more than 3 drops of indicator used - could react with acid

All burette readings are to precision

solution a is titrated against solution B - what solution is in conical flask and what’s in the burette?

Solution A is in conical flask

Solution b is in burette

What should you record the titre volumes to

Titre volumes should be recorded to 2 dp

If a burette had an uncertainty of +- 0.05 for each reading then what’s the overall uncertainty

0.10

How can u reduce uncertainty with titration

Replace measuring cycliners with pipettes or burette - lower apparatus uncertainty

To reduce uncertainty in burette - titre volume needs to be larger

• by increasing volume + conc of solution in flask

• Or by decreasing conc of substance in burette

How would titre volume change if water is added to burette,pipette,flask

Burette - titre value increases

• the conc decreases of alkali

• The volume needed is higher to get the moles needed to neutralise the acid

Pipettes - tire value decreases

• conc decreases

• Pipettte has fixed volume

• Moles = conc x volume so the moles is lower

• Meaning there is less to be neutralised = lower titre value

Flask - titre value stays same

• the conc decrease and volume increaes overall in flask

• But because its the moles of the acid that needs to be titred - that remains same

• Water doesn’t react with acid - doesn’t remove any of the acid particles = moles same = titre value same