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Chemistry > Required Practical 1 - Volumetric Solution + Titration > Flashcards

Required Practical 1 - Volumetric Solution + Titration Flashcards

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1
Q

Volumetric Solution

A
  • Weigh known mass of solid using weighing bottle and record value
  • Wash all into beaker using distilled water
  • Dissolve in beaker by stirring with glass rod
  • Wash out into a 250cm3 volumetric flask
  • Add dropwise with teat pipette to marking/meniscus
  • Fasten and invert flask several times
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2
Q

Titration

A
  • Pipette a known volume of solution of an unknown concentration into a conical flask
  • Add a few drops of phenolphthalein indicator
  • Add volumetric solution to burette using a funnel
  • Record start volume to 2 dp
  • Titrate solution from burette until first permanent colour change
  • Record rough titre to 2 dp
  • Repeat until three results are recorded within 0.1cm3 to calculate a mean titre
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3
Q

Suggest a reason for having a rough titre

A

Allows a rough estimate to made for the titre so repeats can be titrated dropwise near that value to obtain an accurate result

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4
Q

Give a reason why rough titres are not included in calculating mean titre

A

Not within 0.1cm3 of other titres

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5
Q

Give hazards and safety precautions for acid-base titrations

A
  • corrosive so wear eye protection/gloves

- irritant vapour so handle in fume cupboard

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6
Q

Suggest how you could reduce percentage uncertainty of titre and justify your choice

A
  • More concentrated standard solution in conical flask

- Larger titre reading

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7
Q

Improvements for preparation of volumetric solution

A
  • Wash out weighing bottle/beaker/stirring rod/funnel using distilled water (into volumetric flask)
  • Use a teat pipette to make up mark on volumetric flask
  • Invert flask
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8
Q

Purpose of titration

A
  • determine concentration of a basic solution

- detect equivalence point for a acid-base reaction

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9
Q

Suggest why it is not important to fill burette to zero mark

A

Volumes are determined from difference between initial and final readings

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10
Q

Suggest significance of touching off hanging drop after closing burette

A

Liquid on tip of burette is part of volume delivered by burette

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11
Q

Suggest why you should not leave the funnel in the burette

A
  • small drops of liquid might fall into the burette

- mean titre is lower than actual titre

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12
Q

Suggest why burette and pipette are rinsed with reagents they hold before titration

A
  • ensure only appropriate reagent present
  • prevent contamination or dilution of solution by water or other chemicals
  • removed any air bubbles trapped in valve
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13
Q

Suggest why two or three drops of indicator are added to conical flask

A
  • too little means colour is not visible

- too much could impact pH thus cannot determine true end point of reaction

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14
Q

Suggest why it is important to take burette reading at eye level or below meniscus

A

Avoid parallax error

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15
Q

Suggest why a conical flask is used in a titration rather than a beaker

A

Easier to swirl without losing liquid

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16
Q

Suggest why a burette is appropriate to use in an acid base titration

A
  • can control amount of liquid released
  • allows for extremely accurate addition of liquid
  • precise readings can be taken
17
Q

Purpose of volumetric pipette

A

Measuring and transferring an exact volume

18
Q

Explain what is meant by concordant results

A
  • within 0.1 od each other

- reproducible, consistent results

19
Q

Suggest how to obtain an accurate average titre

A
  • do further titrations (at least three)

- must be concordant

20
Q

Suggest how you can accurately measure volume in burette

A
  • take reading at eye level or below meniscus

- hold while tile behind burette so it is easier to read

21
Q

Explain why using a burette increases the precision of the titration

A
  • burette has high precision (scale measure in 0.1cm^3)

- precision is limited by scale of instrument used

22
Q

Suggest why distilled water is used to wash conical flask near end point of titration

A
  • returns reagent on sides of flask to reaction mixture

- ensure reagent is full reacted to give accurate end point

23
Q

What effect will adding distilled water to conical flask near end point of titration have on titre

A
  • no effect
  • number of moles of solution does not change (only diluted)
  • colour change determined by moles of solution
24
Q

Suggest why concordant results are used to calculate mean titre

A
  • within 0.1cm^3 of each other
  • more reliable mean titre calculated
  • reduced human error in titration
25
Q

Suggest why conical flask should be rinsed with distilled water before titration

A
  • holds certain number of moles of standard solution

- rinsing removes any residues that could add to the number of moles of solution

26
Q

Suggest effect of bubble in burette on titre reading

A
  • titre reading will be higher than actual titre

- when bubble bursts volume decreases but no reagent is added

27
Q

How to calculate percentage error of equipment

A

Sum of individual percentage errors of equipment used

28
Q

Describe steps taken during the titration procedure that help to ensure that accurate results are obtained

A
  • conical flask rinsed with distilled water
  • burette and pipette rinsed with reagents they hold
  • funnel is removed once solution is transferred to burette
  • only a few drops of indicator added to conical flask
  • conical flask is swirled
  • ensure burette has no air bubbles
  • readings for burette are taken at eye level or below meniscus
  • white tile held behind burette when readings taken
  • distilled water used to wash sides of conical flask near end point
  • solution is added dropwise near end point of titration
29
Q

Suggest why it is important to fill the space below the burette tap with solution before beginning a titration

A
  • space will fill during titration
  • volumes added will be too large
  • titre larger than true value
30
Q

Suggest why it is important to carry our repeat titrations

A
  • repeats improve reliability

- single titration could be anomalous

Chemistry (10 decks)

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