Volumetric Analysis Flashcards

1
Q

Accuracy

A

Measure of the closeness of agreement between individual test result and the true value

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2
Q

Error

A

Difference between individual measurement and the true value of the quantity being measured

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3
Q

Precison

A

Closeness of agreement between independent measurements obtained under the same conditions

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4
Q

Uncertainty

A

Estimate attached to a measurement to characterise range of values within which the true value is asserted to lie

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5
Q

Anomaly

A

Value in set of results judged to not be part of inherent variation

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6
Q

Confidence

A

Qualitative judgement expressing extent to which a conclusion is justified by the quality of the evidence

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7
Q

Repeatability

A

Precision obtained when measurement results are produced over a short period of time by 1 person / group with same equipment/ same place

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8
Q

Reproducibility

A

Precision obtained when measurement results are produced over a wider timescale by different people using equivalent equipment, in different but equivalent places

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9
Q

Resolution

A

Smallest change in the quantity being measured that can be detected by an instrument

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10
Q

Validity

A

Measurement if it measures what it’s supposed to be measuring

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11
Q

Standard solution

A

Solution that has a precisely known Concentration. Made by dissolving a known amount of solid in a known amount of water

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12
Q

Steps of standard solution

A

Weigh crucible and solid to find exact mass
Dissolve in distilled water + stir
Rinse beaker x3 to ensure all solid transfers to volumetric flask
Invert flask - ensure conc is the same throughout
Meniscus at eyelevel

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13
Q

Titration

A
  1. Rinse pipette with distilled water to remove unwanted chemicals
  2. Rinse with (alkali) to remove water
  3. Flask next to beaker containing alkali after being rinsed with distilled water - traces of water won’t interfere with reaction
  4. Measure slightly over 25cm3 of alkali as it will drop a little as you lift from alkali. Then release drops to get accurate 25 (bottom of meniscus)
  5. Release alkali into conical flask, is some is left in pipette touch it to alkali surface in flask and it will drip out
  6. Indicator for acid based tritagions . Eg (weak acid amd string base, use phenolphthalein. Strong aicd weak base - methyl orange)
  7. Only add a few drops of indicator- they are weak acids so may give inaccurate result if too much
  8. Rinse burette with water to remove unwanted chemicals then acid to remove water
  9. Clamp burette so it’s level.
  10. Use funnel to add acid ( analyte), slightly above 0
  11. Open tap to get acid to 0
  12. Conical on white tile below
  13. Open tap. Swirl conical - mix , react.
  14. Stop adding aicd at colour change - end point
  15. Read level on burette - scale markings to nearest 0.1cm3, analog so uncertainty 0.05cm3 - record to newest 0.05
  16. Start vol - end vol = titre = rough
  17. Rinse flask and repeat
  18. Add aicd drop by drop if near
  19. Repeat until 2 concordant results - within 0.1cm3
  20. Find mean of concordant.
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14
Q

Titration equipment measurements

A

Burette - 50cm3
Conical - 250cm3
Graduated pipette - 25cm3
Volumetric flask - 250cm3

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15
Q

Uncertainty of 250/100/50 cm3 measuring cylinder

A

1cm3

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16
Q

Uncertainty 10cm3 measuring cylinder / 250cm3 vol flask

A

0.2cm3

17
Q

Uncertainty graduated pipette 25cm3

A

0.06cm3

18
Q

Uncertainty of equipment

A

Indication of accuracy of measurement

19
Q

% uncertainty

A

( Absolute uncertainty / measurement )
x100

20
Q

Reduced uncertainty

A
  1. Increase measurement:
    (Denominator)
  2. Decrease uncertainty:
    (Numerator)
    Increase precision of equipment
21
Q

Uncertainty of digital device

A

Smallest scale division

22
Q

Analogue device uncertainty

A

Half smallest scale division

23
Q

Recording from burette

A

Always to 2dp - either 0 or 5

24
Q

Total uncertainty

A

Add uncertainty of al measurements
Ex. Mass before … (+-0.1)
Mass after… (+-0.1)
Total… (+-0.2)