Topic 11 - Measurement & Data Processing

half of the smallest division visible on the scale e.g. when measuring the volume on water on a measuring cylinder divided with a scale of 4ml, use ± 2ml

the smallest scale division on the scale e.g. when measuring weight and the reading says 10.00g, use 10.00 ± 0.01g

• instrument readings • uncertainties in judging (especially with qualitative data) • errors

• all the figures involved in the reading e. g. 10.00 has 4 significant figures as the .00 denotes the level of uncertainty

• random - systematic

• readability of measuring instrument • effects of changes in surrounding (e.g. temperature variations) • insufficient data • misinterpreted readings

repeated trials

if the experimenter can duplicate the experiment and observes the same results

if different experimenters can duplicate the experiment and observe the same results

poor experimental design/procedure e. g. measuring the volume of water from the top of the meniscus instead of the bottom e. g. using an acid–base indicator whose end point does not correspond to the equivalence point of the titration

careful experimental design

smaller systematic error = higher accuracy • small systematic errors • gives result close to accepted value

smaller random uncertainties = greater precision • small random errors • reproducible

x-axis: independent variable y-axis: dependent variable

• should pass as close as possible to many data points • doesn’t have to pass through all • can be used for extrapolation

• absolute zero value can be found - by extrapolating the vol/temp graph for an ideal gas

the assumption that the trend line applies between 2 points

presence of outliers indicate that data may not be reliable

• qualitative • quantitative • structural

used to identify the bonds in a molecule

used to: • determine relative atomic and molecular masses • can also be used to identify unknown substances or as evidence for atomic arrangements in a molecule (like a fingerprint) • thus one can derive a molecule’s molecular formula

• used to show the chemical environment of certain isotopes in a molecule • nucleis of atoms with odd numbers of protons have the ability to spin and behave like tiny bar magnets • they will line up with an applied field when placed in a magnetic field • this leads to 2 energy states (higher/lower) • radio waves provide energy needed for the nuclei to reverse their spin and change their orientation in a magnetic field • gives vital info about structures • as the samples are unchanged, NMR is non-invasive

• ionization step involves shooting an e- at the incident species and removing an e- from the species • the collision may be so energetic that it causes the species to break apart • some parent ions can pass through unscathed • but individual ions produced as a result of the breakup can also be detected • a chemist can piece the fragments together based on the data of their mass • to form a picture of the complete molecule

AKA Index of Hydrogen Deficiency (IHD) • measure of how many molecules of H are required to convert the molecule to the corresponding saturated, non-cyclic molecule • provides a useful clue for the structure of a molecule once its formula is known