Chapter 0: The Analytical Process

Aliquot

Portion

Analyte

Substance being measured or detected

Aqueous

In water (in an aqueous solution)

Calibration curve

A graph showing the value of some property versus concentration of analyte. When the corresponding property of an unknown is measured, it's concentration can be determined from the graph. Also called a standard curve.

Composite sample

A representative sample prepared from a heterogeneous material. If the material consists of distinct regions, it is made of portions of each region, with relative amounts proportional to the size of each region.

Decant

To pour liquid off a solid or, perhaps, a denser liquid. The denser phase is left behind.

Heterogeneous

Having a composition that is not uniform throughout.

Homogeneous

Having the same composition everywhere.

Interference

A phenomenon in which the presence of one substance changes the response in the analysis of another substance.

Masking

Process of adding a chemical substance to a sample to prevent one or more components from interfering in a chemical analysis.

Qualitative chemical analysis

Process of determining the identity of the constituents of a substance.

Quantitative chemical analysis

process of measuring how much of a constituent is present in a substance

Quantitative transfer

Transfer of the entire contents from one vessel to another. This process is usually accomplished by rinsing the first vessel several times with fresh liquid and pouring each rinse into the receiving vessel.

Random transfer

Is collected by taking portions from the desired number of segments chosen at random.

Random heterogeneous material

A material in which there are fine-scale differences in composition with no pattern or predictability. When you collect a portion of the material for analysis, you obtain some of each of the different compositions.

Random sample

Bulk sample constructed by taking portions of the entire lot at random

Sample preparation

transforming a sample into a state that is suitable for analysis. This process can include concentrating a dilute analyte and removing or masking interfering species.

Sampling

The process of selecting a representative sample for analysis

Segregated heterogeneous material

A material in which differences in composition are on a large scale. Different regions have obviously different composition.

Slurry

a suspension of a solid in a solvent.

Species

Chemists refer to any element, compound, or ion of interest as this. Can be both singular and plural.

Standard solution

A solution whose composition is known by virtue of the way that it was made from a reagent of known purity or by virtue of its reaction with a known quantity of a standard reagent.

Supernatant liquid

liquid remaining above the solid after a precipitation.

What is the difference between qualitative and quantitative analysis?

Qualitative analysis involves detecting the composition of a sample.

Quantitative analysis is the determination of the unknown quantities of the substance in the sample.

What? - qualitative

How much? - quantitative

First step in a chemical analysis.

Formulating the question

What does it mean to mask an interfering species?

to remove it's interfering ability by some sort of chemical manipulations

What is the purpose of a calibration curve?

A graph that we can get from standard solution analysis, and its purpose is to give us a graph and a detector response value that can be used as the reference value.

What is the difference between a homogenous material and a heterogeneous material?

One is a material whose composition is the same as the entire sample (eg. drinking water, clear juice).

One is the material whose composition is not the same in the entire sample and varies from one place to another (eg. juice with pulp, gravel).

State the difference between a segregated heterogeneous material and a random heterogeneous material.

One has a heterogeneous composition of the whole sample, and heterogeneity occurs randomly and without any rules.

One is whose heterogeneity is manifested by the appearance of the region's in the sample, whose composition and percentage distribution vary.

Second step in chemical analysis

Selecting the proper analytical procedure

Third step in chemical analysis

Sample preparation

Fourth step in chemical analysis

Chemical Analysis

Fifth step in chemical analysis

Reporting and interpretation

Sixth step in chemical analysis

Drawing conclusions

How would you construct a representative sample from a random heterogeneous material?

it is necessary to assign the entire material in many parts, and then randomly take these parts to the formation of the sample that is to the desired amount of sample.

How would you construct a representative sample from a segregated heterogeneous material?

it is necessary to Irwin the same ratio of the region's in the sample as there are in the whole material.