Unit 2 Flashcards
A vital step in any quantitative analysis
Select a Method
3 considerations in selecting a method
- The level of accuracy required
- The number of samples to be analyzed
- Complexity and number of components in the sample
the most important to be considered in the
selection
The level of accuracy required
True or False
Low reliability always requires a large invest
of time
False, high reliability
True or False
The selected method usually represents a
compromise between the accuracy required and the time and money available for the analysis
True
Consideration of selecting a method related to economic factors
The number of samples to be analyzed
What to do when there are many samples?
spend a significant amount of time in preliminary operations just assembling and calibrating instruments and equipment, and preparing a standard solution
What to do when there is only a single or few samples?
it is appropriate to select a procedure that avoids or minimizes such preliminary steps
Consideration of selecting a method which Influences the choice of method to some degree
Complexity and number of components in the sample
True or False
To produce meaningful information, an analysis must be performed on a sample that has a different composition as the bulk material from which it was taken.
False, same composition
Most difficult step in analysis and source of greatest error; must done carefully
Sampling
Challenges in sampling
Bulk samples
Heterogenous sample
Samples from biological sources
Give the types of samples to collect
Grab samples
Composite samples
In situ
A single sample or measurement taken at a specific time or over a short period as feasible
Grab samples
Involves taking several individual sampling units and mixing them before measuring, counting or analyzing the composite sample
Composite samples
measurement is taken in the same place the
phenomenon is occurring without isolating it from other systems or altering the original conditions of the test
In situ
True or False
The final analytical result will never be any more reliable than the reliability of the
sampling step.
True
Is sample processing required when a sample is water withdrawn from a stream?
No, the pH of the sample can be measured directly.
ground to decrease particle size, mixed to assure homogeneity, and stored for various lengths of time before the analysis begins
Solid laboratory sample
the process by which ions, atoms or molecules adhere to the surface of the solid material
Adsorption
the release of an adsorbed substance from a surface
Desorption
What to do with samples with volatile solvent?
it must be kept in sealed containers
solvents that are easily evaporated at normal temperatures
Volatile solvent
involve mixing the sample and forming the solid material into a conical heap upon a solid surface followed by flattening the heap and dividing into four equal parts. two opposite quarters are taken as sample while the other two are discarded or set aside
Coning and quartering
- Involves dividing the sample into two approximate equal parts with the use of a riffler
- Particularly useful with large samples which are normally more difficult to sub-sample
Riffling
improves the quality of the results and provides a measure of the of their reliability
replication
True or False
ideally, the solvent should dissolve the entire sample (not just the analyte) rapidly and completely
True
Consideration when Preparing Solutions of the Samples
the end result of these conversions must leave the sample with a measurable property that is proportional to analyte concentration
species other than the analyte that affect the final measurement
Interference/Interferents
Should the interferences be removed? Why or why not?
Yes, Interferences must be removed before a measurement is to be done. Because they cause an error to the final measurement
the measurement of the physical property is ______ proportional to the concentration
Directly
Formula for conectration
𝐶 =𝑘𝑋
What is k in the formula? Thank
k is the proportionality constant
The process of determining k
Calibration
Ordinarily a simple and straightforward task particularly with modern calculators and computers
Calculating Results
computations are based on:
- the raw experimental data collected in the
measurement step - the stoichiometry of the chemical reaction
upon which the analysis is based - instrumental factors
analytical results are incomplete without ______
an estimate of their reliability
A sampling technique in which each member of the subset has an equal probability of being chosen
Random sampling
a non-probability sampling technique in which the sample members are chosen only on the basis of the researcher’s knowledge and judgment
Judgmental sampling
a type of probability sampling method in which sample members from a larger population are selected according to a random starting point but with a fixed, periodic interval
Systematic sampling
a method of sampling that involves the division of a population into smaller sub-groups known as strata
Stratified sampling
a method adopted by researchers where they collect market research data from a conveniently available pool of respondents
Convenience sampling
