Volumetric Analysis Flashcards
Accuracy
Measure of the closeness of agreement between individual test result and the true value
Error
Difference between individual measurement and the true value of the quantity being measured
Precison
Closeness of agreement between independent measurements obtained under the same conditions
Uncertainty
Estimate attached to a measurement to characterise range of values within which the true value is asserted to lie
Anomaly
Value in set of results judged to not be part of inherent variation
Confidence
Qualitative judgement expressing extent to which a conclusion is justified by the quality of the evidence
Repeatability
Precision obtained when measurement results are produced over a short period of time by 1 person / group with same equipment/ same place
Reproducibility
Precision obtained when measurement results are produced over a wider timescale by different people using equivalent equipment, in different but equivalent places
Resolution
Smallest change in the quantity being measured that can be detected by an instrument
Validity
Measurement if it measures what it’s supposed to be measuring
Standard solution
Solution that has a precisely known Concentration. Made by dissolving a known amount of solid in a known amount of water
Steps of standard solution
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
Titration
- Rinse pipette with distilled water to remove unwanted chemicals
- Rinse with (alkali) to remove water
- Flask next to beaker containing alkali after being rinsed with distilled water - traces of water won’t interfere with reaction
- 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)
- Release alkali into conical flask, is some is left in pipette touch it to alkali surface in flask and it will drip out
- Indicator for acid based tritagions . Eg (weak acid amd string base, use phenolphthalein. Strong aicd weak base - methyl orange)
- Only add a few drops of indicator- they are weak acids so may give inaccurate result if too much
- Rinse burette with water to remove unwanted chemicals then acid to remove water
- Clamp burette so it’s level.
- Use funnel to add acid ( analyte), slightly above 0
- Open tap to get acid to 0
- Conical on white tile below
- Open tap. Swirl conical - mix , react.
- Stop adding aicd at colour change - end point
- Read level on burette - scale markings to nearest 0.1cm3, analog so uncertainty 0.05cm3 - record to newest 0.05
- Start vol - end vol = titre = rough
- Rinse flask and repeat
- Add aicd drop by drop if near
- Repeat until 2 concordant results - within 0.1cm3
- Find mean of concordant.
Titration equipment measurements
Burette - 50cm3
Conical - 250cm3
Graduated pipette - 25cm3
Volumetric flask - 250cm3
Uncertainty of 250/100/50 cm3 measuring cylinder
1cm3
