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QUALITY CONTROL FINAL EXAM PART 1 (OBJECTIVE)

TERMS

TITRIMETRIC METHODS those analytical methods in which the volume of asolution of known concentration consumed during an analysis is taken as a

measure of the amount of active constituent in a sample being analyzed.

TITRANT solution of known concentration TITRATION the act of adding and measuring the volume of titrant used in the

assay INDICATOR a chemical which changes color at or very near the point in the

tritration where equivalent quantities of analyte and titrant have reached.

STOICHEMETRIC POINT / EQUIVALENCE POINT the theoretical point at whichequivalent amounts of each have reacted

END POINT point at which there occurs a sudden change in some property of thereaction mixture

GRAM EQUIVALENT WEIGHT weight in grams which is chemically equivalent to1 gram-atom of hydrogen

NORMALITY number of equivalents of solute per liter (equiv/L) or (meq/mL) MOLARITY moles per liter of solution MOLALITY moles per kg of solvent TITER weight of a substance chemically equivalent to 1mL of a standard solution PRIMARY STANDARD carefully weighed sample of a substance of known purity ACIDIMETRY the direct or residual titrimetric analysis of bases using an

accurately measured volume of acid

KJELDAHL METHOD determination of other organic compounds containingnitrogen

OXIDATION-REDUCTION METHOD involve a change in valence of the reactingsubstances.

ACTIVITY OF AN ION term used to designate effective concentration and isrelated to the actual equilibrium conc. Of each chemical species by the following

AMPHOTERIC / AMPHIPROTIC can act either as an acid or base GRAVIMETRIC ANALYSIS the measurement of the weight of a substance in a

sample or calculation of the weight of a substance in a sample from the weight of a

chemically equivalent amount of some other substance

LAW OF MASS ACTION the rate of a reaction is proportional to the product ofthe molecular concentrations of the reacting substances.

ELECTRONEUTRALITY RULE determines the total hydronium-ion concentrationin any solution

pH the negative logarithm of hydrogen ion conc. GRAVIMETRIC / CHEMICAL FACTOR mol. Wt 1 / mol. Wt. 2 PROTOLYSIS a process where a proton is transferred from one molecule to

another

CONJUGATE ACID CONJUGATE BASE

SIMPLE RECALL:

1. Differentiate betweena. volumetric method of analysis and gravimetric method of analysisb. acidimetry and alkalimetry

i. acidimetry - the direct or residual titrimetric analysis of basesusing an accurately measured volume of acid

ii. alkalimetry acid is estimated quantitatively by methodsanalogus to those employed in the quantitative estimation of

bases by treating the acid to a standard alkali solution.

c. Bronsted-Lowry definition of an acid and a based. Arrheneous theory of the definition of an acid and basee. gram-equivalent weight and gram-milliequivalent weight

i. Gm-eq. wt. weight in grams which is chemically equivalent to 1gram-atom of hydrogen

ii. Gm-meq. Wt. GEW / 1000f. direct titration and residual titration

i. Direct titration conducted by introducing a standard acidsolution gradually from a buret into a solution of the bases being

assayed until chemical equivalent amounts of each have reacted

as shown by some change in properties of the mixture.ii. Residual titration done in which the basic sample is treated

with an amount of standard acid known to be in excess of a

chemically equivalent amount, and the excess acid is

subsequently titrated with a standard base.

g. oxidizing agent and reducing agenti. oxidizing agent the reactant containing a constituent atom/s

which are converted to a lower state of oxidation

ii. reducing agent the reactant which loses electrons in anoxidation-reduction reaction

2. Method of analysis considered as oxidation-reduciton method- Ex. Permanganate process and Dichromate process ?

3. The general conditions that will prevent reversal and lead to completion reactiona. The formation of an insoluble gasb. The formation of a sparingly soluble solidc. The formation of very slightly ionized molecules

4. A reaction that will illustrate (determination of the) equation of the chemicalequilibrium constant in the system.

5. Why is the mixture of silver chloride placed in a dark room instead of exposing it tosun light?

- To minimize the reducing effect of the light on silver chloride producingfree silver. The purplish color w/c the ppt. acquires on exposure to light is due

to the free metal being formed in the precipitate.

7/28/2019 Qc1 - Final Exam (Objective)

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Q.C

1.) Titrimetric Methods of Analysis- as those analytical methods in which the volume of a solution of

known concentration consumed during an analysis is taken as a measure of the amount of active

constituent in a sample being analyzed.

2.) Titration- act of adding & measuring the volume of titrant used in the assay

3.) Titrant-solution of known concentration added by means of a buret

4.) Indicator- a chemical which changes color at or very near the po int in the titration where equal

amounts of analyte & titrant have reacted; complex organic compds. Used to determine the end

points in neutralization processes, to determine pH & to indicate a desired change in pH has been

affected.

5.) StochoimetricPoint (equivalence point)-the theoretical point where equivalent amounts of the

titrant & analyte have reacted

6.) End point- a point where a sudden change in some property of the reaction mixt. Occurs (titration

the is terminated)

7.) Gram eq. weight- the gram equiv. of a chemical is defined as that weight in grams which is

chemically equivalent to 1 gram atom of Hydrogen (1.0079); In neutralization rxns, it is defined as the

weight of a substance in grmas which contains,furnishes & reacts with directly or indirectly, or

replaces 1 gram-atom or ion of Hydrogen.

8.) Molarity- a conc. expression in terms of moles per liter.

9.) Normality- a conc. expression & is defined as the no. of equivalents of solutes per liter or meq. Per

ml of solution.

10.) Molality- number of moles of solute per 1000g of solvent11.) Titer- weight of the substance chem.. equivalent to 1 ml of a standard solution.

12.) Primary Standard- a carefully weighed sample of a substance of known purity

13.) Acidimetry- the direct or residual titrimetric analysis of bases using an accurately measured

volume of acid (supplied in the analytical control of a considerednumber of official substances both

organic & inorganic)

14.) Kjehdahl Method- determination of Nitrogen in organic compounds

15.) Oxidation-Reduction- involve a transfer of electrons & change in valence of the reacting

substances; Gain & loss of electrons

16.) Activity- used to designate effective concentration & is related to the actual equilibrium

concentration of each chemical species by the ff. equation: ( ai= fi [Ai] )

17.) Amphiprotic- water; a subs. That can act as either an acid or base

18.) Gravimetric Analysis- measurement of the weight of a substance in a sample or calculation of the

weight of a from the weight of a chemically equivalent amount of some other substance

19.) Law of Mass Action- the rate of a reaction is proportional to the product of the molecular

concentrations of the reacting substances.

20.) Electroneutrality- to determine the total hydronium ion concentration in any solution, it is most

exact to employ this rule: a given solution is electrically neutral, & therefore to tal positive charges

must equal to total negative charges.

21.) pH- logarithm of the reciprocal of the hydrogen ion activity

22.) protolysis- a process whereby a proton is transferred from one molecule to ano ther ( protolytic

rxn)

23.) conjugate acid- seen as the chemical substance that releases or donates a proton (hydrogen ion)

in the forward chemical reaction, hence, the term acid. substance formed when a base gains a

hydrogen ion

24.) conjugate base- it absorbs, or gains, a proton in t he backward chemical reaction. substance

formed when an acid loses a hydrogen ion

25.) gravimetric factor- chemical factor; is included in the official gravimetric assay procedures.

II)

1. Differentiate Volumetric from gravimetric Methods of analysis.

Titrimetric Methods of Analysis (Volumetric) are those analytical methods in which the volume of a

solution of known concentration consumed during an analysis is taken as a measure of the amount of

active constituent in a sample being analyzed. Gravimetric Analysis is the measurement of the weight

of a substance in a sample or calculation of t he weight of a from the weight of a chemically equivalent

amount of some other substance (precipitation from solution; decomposition product resulting from

ignition of a compound & may be deposited on an electrode by electrolysis)

2. Differentiate Direct from Residual Titration

Direct Titration is conducted by introducing a standard acid solution gradually from a buret into a

solution of the base being assayed until chemical equivalent amounts of each have reacted. Residual

titration is used whenever a reaction proceeds slowly or when the substance to be assayed does not

give a distinct, sharp end point with an indicator by direct titration. It is carried out by dissolving y the

substance under examination in an accurately measured quantity od standard solution known to be in

excess and titrating the excess of the latter with another standard solution.

3. Differentiate between Acidimetry from Alkalimetry

Acidimetry is the direct or residual titrimetric analysis of bases using an accurately measured volume

of acid (supplied in the analytical control of a considered number of official substances both organic &

inorganic). Alkalimetry on the other hand, is the direct or residual titrimetric analysis of acids (by

directly titrating an exact quantity of the acid, acid sa lt, pr other acidic substance with standard alkali

solution or by adding an excess of the latter and determining the amount in excess by residualtitration with a standard acid solution.)

4. Bronsted-lowrys definition of an acid & a base-

According to this theory, an acid is defined as an ionic or molecular substance capable of giving up a

proton (proton donor). A base is defined as an ionic or molecular substance capable of uniting with

a proton (proton acceptor).

5. Aurrhenius Theory-

Acids are substances which produce hydrogen ions in solution. Bases are substances which produce

hydroxide ions in solution. Neutralisation happens because hydrogen ions and hydroxide ions react

to produce water.

6. Methods of Analysis considered as REDOX

*Permanganate Method *Ceric Sulfate Titration Methods *Iodometric Method *Iodimetric Method

7. 3 general considerations that will tend to prevent reversal & lead to completion of a chemical

reaction are:

*The formation of an insoluble gas *The formation of a sparingly soluble solid *The formation of

very slightly ionized molecules

8. A reaction that will illustrate the determination of a chemical equilibrium constant(refer to your

book: gravimetric Methods of Analysis..& lecture ni Engr.)

9. Differentiate Oxidizing from Reducing agents

Oxidizing agent gains the electrons lost by the reducing agent. The reactant which loses electron in an

Oxidation-Reduction reaction is the reducing agent.

10. Why is the mixture of Silver Chloride placed in dark areas instead of exposing it to sunlight?

The mixture is allowed to stand in the dark to minimize the reducing effect of the light on Silver

chloride; free silver is produced. The purplish color which the precipitate acquires on exposure to

light is due to the free metal being formed in the precipitate.

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