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Analytical Chemistry > Gravimetric Analysis 1-2 > Flashcards

Gravimetric Analysis 1-2 Flashcards

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1
Q

Are quantitative methods based on determining the mass of a pure compound to which the analyte is chemically related.

A

GRAVIMETRIC METHODS

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2
Q

What are the four types of gravimetric methods?

A
  1. Precipitation gravimetry
  2. Volatilization gravimetry
  3. Electrogravimetry
  4. Gravimetric titrimetry
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3
Q

It is the most common type of gravimetry. The analyte is separated from a solution of the sample as a precipitate and is converted to a compound of known composition that can be weighed.

A

Precipitation gravimetry

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4
Q

The analyte is separated from other constituents of a sample by converting it to a gas of known chemical composition. The mass of gas serves as a measure of the analyte concentration.

A

VOLATILIZATION GRAVIMETRY

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5
Q

The analyte is separated by deposition on an electrode by an electric current and the mass of this product provides a measure of the analyte concentration.

A

ELECTROGRAVIMETRY

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6
Q

The mass of the reagent unknown concentration required to react completely with the analyte provides the information needed to determine the analyte concentration.

A

GRAVIMETRIC TRITRIMETRY

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7
Q

The analyt is converted to a sparingly soluble precipitate

A

PRECIPITATION GRAVIMETRY

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8
Q

The precipitate is filtered, washed free of impurities, and converted to a product of known composition by suitable heat treatment and weighed.

A

PRECIPITATION GRAVIMETRY

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9
Q

This agent of precipitation gravimetry should ideally react specifically or selectively with the analyte.

A

GRAVIMETRIC PRECIPITATING AGENT

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10
Q

In gravimetric precipitation agent of precipitation gravimetry, what kind of reagents are rare and react only with a single chemical species?

A

SPECIFIC REAGENTS

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11
Q

In gravimetric precipitation agent of precipitation gravimetry, what kind of reagents are more common and react with a limited number of species?

A

SELECTIVE REAGENT

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12
Q

Precipitating agent that would react with analyte to give a product that is **easily filtered and washed free of contaminants, low solubility, unreactive with constituents of the atmosphere, and of known chemical composition after dried or ignited.

A

IDEAL PRECIPITATING AGENT

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13
Q

What is the preferable size of particles, large or small. IT MUST BE EASY TO FILTER AND MUST BE PURER THAN FILTRATES.

A

LARGE PARTICLES

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14
Q

What are the two types of precipitates?

A

Colloidal and crystalline

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15
Q

Solid particles with less than 10^-14cm in diameters

A

Colloid

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16
Q

Tiny particles invisible to naked eye (10^-7 to 110^-4cm)

A

Colloidal suspension

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17
Q

Show no tendency to settle and difficult to filter

A

Colloidal particles

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18
Q

Colloidal suspensions may be perfectly clear in diffuse light but the presence of the second phase can be detected by shining a flashlight into the solution.

A

Tyndall effect

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19
Q

It is larger than a colloid. It describes a solution in which particles with dimensions on the order of a tenth of a millimeter or greater are temporarily dispersed in the liquid phase. The particles *tend to settle+ and easily filtered

A

Crystalline suspension

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20
Q

It is an unstable solution that contains a higher solute concentration than saturated solution. Solutions are likely because precipitation reactions are so low.

A

SUPERSATURATED SOLUTION

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21
Q

Calculates relative supersaturation. Lower value means crystalline precipitate. Higher value means colloidal precipitate.

A

Von Weimarn Ratio Q-S/S

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22
Q

The process by which a minimum number of atoms, ions, or molecules join together to give a stable solid.

A

Nucleation

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23
Q

Particle grows both by

A

Additional nucleation and growth of existing particles.

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24
Q

If _______ predominates, the resulting precipitate contains many small particles. If ______ predominates, the resulting precipitate contains large particles.

A

Nucleation, growth

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25
Q

Factors that minimize supersaturation and thus produce crystalline growth include:

A

Elevated temperatures, dilute solutions, slow addition of precipitating agent

26
Q

TRUE OR FALSE: If solubility of the precipitate depends on pH, larger particles can be produced by controlling pH.

A

TRUE

27
Q

Many precipitates cannot be formed as crystals under ____________.

A

Laboratory conditons

28
Q

Can be hastened by heating, stirring, and by adding in electrolyte to the medium

A

Coagulation

29
Q

A process by which a substance is held on the surface of a solid.

A

ADSORPTION

30
Q

Is the retention of a substance within the pores of a solid.

A

Absorption

31
Q

Is the attached directly to the solid surface.

A

Primary adsorption layer

32
Q

Surrounds the charged particle

A

Counter-ion layer

33
Q

The primarily adsorbed ions and the negative counter-ion layer constitute an ____________ that imparts stability to the colloidal suspension.

A

ELECTRIC DOUBLE LAYER

34
Q

The higher the ______________, the thinner the distance.

A

electrolyte concentration

35
Q

Thick electrical double layer keep them too far apart for the coagulation to occur

A

Concentrated solution

36
Q

They can approach more closely, allowing a coagulated precipitation to appear.

A

Dilute solution

37
Q

They can approach more closely, allowing a coagulated precipitation to appear.

A

Dilute solution

38
Q

Coagulated colloid reverts to its original disperse state.

A

Peptization

39
Q

Removes some electrolyte

A

washing

40
Q

Is the process in which a precipitate is heated in the solution from which it was formed(the mother liquor) and allow to stand in contact with the solution

A

Digestion

41
Q

How to improve the filter ability of the coagulated colloid.

A

Stand for an hour

42
Q

Generally more easily filtered and purified than coagulated colloid.

A

Crystalline precipitates

43
Q

Generally more easily filtered and purified than coagulated colloid.

A

Crystalline precipitates

44
Q

To improve the particle size of crystalline solids, you must

A

minimize Q, maximize S, or both in the von Weimarn ratio

45
Q

Is the process in which normally soluble compounds are carried out of the solution *by a precipitate.

A

Coprecipitation

46
Q
  1. Surface adsorption
  2. Mixed crystal formation
  3. Occlusion
  4. Mechanical entrapment
A

Four types of Precipitation

47
Q

Common and can cause significant contamination of precipitates with large specific surface areas

A

Surface Adsorption

48
Q

A contaminant replaces an ion in the lattice of a crystal

A

Mixed crystal formation

49
Q

A compound is trapped within a pocket formed during rapid crystal growth.

A

occlusion

50
Q

Crystals grow together and trap a portion of the solution in a tiny pocket.

A

Mechanical entrapment

51
Q

Can be used to improve the purity of many coagulated colloids

A

Digestion

52
Q

The filtered solid is redissolved and reprecipitation to reduce the contaminant concentration.

A

reprecipitation

53
Q

Coprecipitated impurities lead to a _______ if the contaminant is not a compound of the ion being determined.

A

Positive error

54
Q

A compound contaminant may produce ______ error

A

Positive or negative

55
Q

Is a process in which a precipitate is formed by slow generation of a precipitating reagent homogeneously throughout a solution.

A

Homogenous precipitation

56
Q

Homogenous precipitation of crystalline precipitates results in

A

Increase in crystal size and improvements in purity

57
Q

A gravimetric precipitate is heated until its mass becomes ______.

A

constant

58
Q

Removes the solvent and any volatile species.

A

Heating

59
Q

Some precipitates are ignited to decompose the solid and produce a compound of known composition called the ________.

A

Weighing form

60
Q

Is the process of recording thermal decomposition curves.

A

Thermogravimetric analysis

61
Q

Are the mass versus temperature curves

A

thermograms

62
Q

The combined constant factors in a gravimetric calculation are called the

A

Gravimetric factor

Analytical Chemistry (1 decks)

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