CHEM: Analytical Chemistry: Introduction Flashcards by arabella erivera

deals with the separation, identification and determination of the components in a sample

Analytical Chemistry

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is particularly concerned with the questions of “what chemicals are present, what are their characteristics and in what quantities are they present?”

Analytical chemistry

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pertains to agreement of an experimental results with true value

Accuracy

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is the measure of reproducibility of data within a series of results.

Precision

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(t or f)

all non-zero digits are significant.

TRUE

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(t or f)
All zeroes between non-zero digits are significant.
Ex. 2,305,079

TRUE

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(t or f)
ALL zeroes which are SIMULTANEOUSLY to the right of the decimal point AND at the end of the number are ALWAYS significant. Ex. 230.507900

TRUE

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(true or false)

Zeroes in between the decimal point and the first (if <1) or last (if >1) non-zero digits are NOT significant. Ex. 0.000239, 235,790,000

TRUE

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is a method of analytical chemistry which seeks to find elemental composition of inorganic compounds and the functional group of organic compounds.

Qualitative Analysis

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in analytical chemistry, the measurements of quantities of substances produced in reactions rather than simply noting the nature of the reactions

Quantitative Analysis

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What is in the sample?
Identification
Composition determination
Ascertainment of impurities

Qualitative Chemistry

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How much is in the sample?
determination of the proportion of
components in a substance

Quantitative chemistry

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Classification of Analysis

I. Based on sample size
II. Based on the extent of determination
III. Based on nature of methods
IV. Based on materials used

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Ultramicroanalysis
•Microanalysis
•Semi-microanalysis
•Macroanalysis
< 1 mg
1 mg – 10 mg
10 mg – 100 mg
100 mg – 1 g

Based on sample size

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Based on the extent of determination

total amount of a class or a group of active plant principles in a given sample.

Proximate analysis

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Based on the extent of determination

Amount of a specific constituent or a single chemical species present in the sample

Ultimate analysis

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Based on the nature of methods

.Classical method
B.Instrumental method
C.Miscellaneous or special method

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Based on the nature of methods

also known as general/ chemical/ wet/ stoichiometric method
–example : titrimetric analysis
gravimetric analysis

classical method

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Based on the nature of methods

more accurate
–based on specific physical or chemical properties of the analyte
–Examples: spectrometry
polarimetry
chromatography

Instrumental method

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Based on the nature of methods

Involves the crude drugs and other natural products
–Examples: Acid value
Ash content
Water content

Miscellaneous or special method

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IV. Based on materials used
titrimetric method

chemical

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IV. Based on materials used

instruments and special apparata

physical

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IV. Based on materials used

use of microorganism and animals and parts thereof

•Biological

Types of Quantitative Analysis

A. Volumetric Analysis
B. Gravimetric Analysis
C. Special Methods
D. Physico-Chemical Methods

Types of Quantitative Analysis analysis involving the measurement of volume of a solution of known concentration required to react with the desired constituent.

Volumetric Analysis

Types of Quantitative Analysis Analysis involving the accurate measurement of weight of substance being determined which may be isolated in pure form or converted to another substance of known composition by making it react quantitatively with another substance usually a precipitant.

Gravimetric Analysis

Types of Quantitative Analysis analysis which require a distinct type of technique such as analysis of crude drugs, assay of fats and fixed oils, assay of volatile oils and assay of alkaloids.

Special Methods

Types of Quantitative Analysis Analysis based on some specific physical or chemical property or properties of the substance being analyzed with the use of instruments such as: spectrophotometer, chromatograph units, polarographer, polarimeter, flourometer.

Physico-Chemical Methods

Specialized Analytical Methods and Equipment moisture content

Dessicator

Specialized Analytical Methods and Equipment purity of substance

Refractometer

Specialized Analytical Methods and Equipment rotatory power

Polarimeter

Specialized Analytical Methods and Equipment physical characterization

Microscopy

Specialized Analytical Methods and Equipment determination of alcohol, protein components, volatile component, alkaloids

Distillation

Specialized Analytical Methods and Equipment moisture content

oven

Specialized Analytical Methods and Equipment moisture content

Moisture Balance

Specialized Analytical Methods and Equipment identity and quantity of component

Chromatography

Specialized Analytical Methods and Equipment identity and purity

Spectroscopy

Specialized Analytical Methods and Equipment quality and quantity of components

Polarography

Specialized Analytical Methods and Equipment determination of amounts required to produce the desired, definite effect

Biological tests

(t or f) According to their properties, cations are usually classified into five groups. –Each group has a common reagent which can be used to separate them from the solution. The separation must be done in the sequence specified, otherwise, some ions of 1st group can also react with 2nd group reagent, so that the solution must not have any ions left from previous groups to obtain meaningful results.

true

(true or false) 1st analytical group of cations consists of ions that form insoluble chlorides. •As such, the group reagent to separate them is hydrochloric acid, usually used at a concentration of 1–2 M. Concentrated HCl must not be used, because it forms a soluble complex ion ([PbCl4]2-) with Pb2+. Consequently the Pb2+ ion would go undetected.

true

true or false The most important cations in 1st group are Ag+, Hg22+, and Pb2+. The chlorides of these elements cannot be distinguished from each other by their colour - they are all white solid compounds. •PbCl2 is soluble in hot water, and can therefore be differentiated easily.

true

true or false Ammonia is used as a reagent to distinguish between the other two. While AgCl dissolves in ammonia (due to the formation of the complex ion [Ag(NH3)2]+), Hg2Cl2 gives a black precipitate consisting of a mixture of chloro-mercuric amide and elemental mercury. Furthermore, AgCl is reduced to silver under light, which gives samples a violet colour.

true

true or false PbCl2 is far more soluble than the chlorides of the other two ions, especially in hot water. •Therefore, HCl in concentrations which completely precipitate Hg22+ and Ag+, may not be sufficient to do the same to Pb2+. •Higher concentrations of Cl- cannot be used for the aforementioned reasons. •Thus, a filtrate obtained after first group analysis of Pb2+ contains an appreciable concentration of this cation, enough to give the test of the second group, viz. formation of an insoluble sulfide. •For this reason, Pb2+ is usually also included in the 2nd analytical group.

true

TRUE OR FALSE The 2nd analytical group of cations consists of ions that forms acid-insoluble sulfides. •Cations in the 2nd group include: Cd2+, Bi3+, Cu2+, As3+, As5+, Sb3+, Sb5+, Sn2+, Sn4+ and Hg2+. •Pb2+ is usually also included here in addition to the first group.

true

true or false he reagent can be any substance that gives S2- ions in such solutions; most commonly used are H2S (at 0.2-0.3 M), CH3CSNH2 (Thioacetamide/ATK)(at 0.3-0.6 M). •The test with the sulfide ion must be conducted in the presence of dilute HCl. •Its purpose is to keep the sulfide ion concentration at a required minimum, so as to allow the precipitation of 2nd group cations alone.

true

true or false If dilute acid is not used, the early precipitation of 4th group cations (if present in solution) may occur, thus leading to misleading results. •Acids beside HCl are rarely used. Sulfuric acid may lead to the precipitation of the 4th group cations, while nitric acid directly reacts with the sulfide ion (reagent), forming colloidal sulfur.

true

true or false The precipitates of these cations are almost indistinguishable, except for CdS which is yellow. •All the precipitates, except for HgS, are soluble in dilute mineral acids. HgS is soluble only in aqua regia, which can be used to separate it from the rest.

true

true or false The action of ammonia is also useful in differentiating the cations. •CuS dissolves in ammonia forming an intense blue solution, while CdS dissolves forming a colourless solution. •The sulfides of As3+, As5+, Sb3+, Sb5+, Sn2+, Sn4+ are soluble in yellow ammonium sulfide, where they form polysulfide complexes.

true

true or false 3rd analytical group of cations includes ions that form sulfides which are insoluble in basic solution. •The reagents are similar to these of the 2nd group, but separation is conducted at pH of 8–9. Occasionally, a buffer solution is used to ensure this pH. •Cations in the 3rd group are, among others: Zn2+, Ni2+, Co2+, Mn2+, Fe2+, Fe3+, Al3+, and Cr3+.

true

true or false Ions in 4th analytical group of cations form carbonates that are insoluble in water. •The reagent usually used is (NH4)2CO3 (at around 0.2 M), the pH should be neutral or slightly basic. •Caution should be taken to properly separate all lower analytical groups beforehand, as many of cations in previous groups also form insoluble carbonates.

true

true or false Cations which are left after carefully separating previous groups are considered to be in the fifth analytical group. •The most important ones are Mg2+, Li+, Na+, K+ and NH4+.

true

Halides are precipitated by silver nitrate; they can be further identified by color. –Sulfates can be precipitated by barium chloride. –Nitrates can be reduced to ammonia.

Detecting Anions

consist of CO32-, HCO3-, CH3COO-, S2-, SO32-, S2O32- and NO2-. •The group reagent for Group 1 anion is HCL(dil) or H2SO4.

1st group of anions

true or false Qualitative inorganic analysis is now used only as a pedagogical tool. •Modern techniques such as atomic absorption spectroscopy and ICP-MS (Inductively coupled plasma mass spectrometry) are able to quickly detect the presence and concentrations of elements using a very small amount of sample.

true