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Analytical Chemistry > Chapter 8 Gravimetric Methods > Flashcards

Chapter 8 Gravimetric Methods Flashcards

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1
Q

coprecipitation

A

adsorption, occlusion or inclusion of impurities along with the desired analyte in a precipitate

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2
Q

adsorption

A

binding of impurities to the surface of a crystal

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3
Q

absorption

A

inclusions or occlusion of impurities within a crystal

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4
Q

digestion

A

letting a precipitate stand with the mother liquor to promote slow recrystallization

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5
Q

peptization

A

breaking up of a precipitate upon washing with water in the absence of an electrolyte

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6
Q

ionic strength

A

sum of product of concentration of different types of ions and electric charges in the solution

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7
Q

solubility

A

maximum amount of solute dissolved in a liter of solution

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8
Q

common ion effect

A

solubility of a partially soluble salt that decreases by the addition of a soluble salt that has an ion in common

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9
Q

Solubility of an ionic compound increase as ionic strength of solution

A

increases

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10
Q

ionic strength of solution increases when salt is

A

added to the solution, solubility of ionic compound also increases

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11
Q

increase in ionic strength will ___ ionic atmosphere around individual ion

A

increasing, shields from other ions and decreases the tendency for ions to bind together

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12
Q

gravimetry

A

QUANTITATIVE method based on the mass measurement of a pure compound chemically related to ANALYTE

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13
Q

crystalline suspension

A

0.1mm or bigger, easy to filter

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14
Q

colloidal suspensions

A

10^-7 -10^-4

difficult to filter

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15
Q

size of particles depends on

A

1) precipitate SOLUBILITY
2) Temperature
3) Reactants concentrations
4) Mixing rate of reactants

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16
Q

Supersaturation

A

Q-S/S
Q>S NO prec
LARGE RSS=Colloidal

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17
Q

nucleation

A

formation of new solid particle

18
Q

particle growth

A

increase in size of particles which already exist

19
Q

type of precipitate depends onw hich process dominates

A

nucleation: many small particles formed (colloidal) RN increases strongly with increased supersaturation

particle growth: fewer and bigger particles are formed, rate increases slightly with increased supersaturation

20
Q

Minimiza Supersaturation

A

increased temperature=increased solubility

dilute solution=minimize instant concentration Q

slow addition

pH control IF s depends on pH

21
Q

make colloids to coagulate=agglomerate

A

increased temp, stirring, external electrolyte

22
Q

Why colloidal precipitates are stable?

A

particles are either + or -

23
Q

peptization

A

during washing ,coagulated colloid goes back to dispersed form

24
Q

coprecipitation

A

normally soluble compounds end up in precipitate causing contamination,

1) surface adsorption
2) mixed crystal
3) occlusion

25
Q

Colloidal vs Crystalline Precipitate

A

a) size: less than 10^-4 vs more than
b) suitability: colloidal are not suitable
c) requirement of pretreatment: colloidal have no tendency of settling so coagulation needs to occur

26
Q

Gravimetric Precipitation vs Volatization

A

Grav: conversion of analyte to sparingle soluble precipitate, filtered and washed free from impurities. Then converted to a product of known composition by suitable heat

Vol: analyte volatilized at a suitable temp, collected, weighed or loss of mass

27
Q

precipitation vs coprecipitation

A

pre: solid phases are obtained and seperated out of solution
co: get precipitated in presence of analyte

28
Q

coagulation vs peptization

A

co: stick colloidal particles together, loss of double layer from electrolye
peptization: reversal coagulation

29
Q

occlusion vs mixed

A

occ: coprecipitation where foreign ion may entrap during crystal growth in the counter ion layer, controlled by digestion
mixed: ion in the lattice of a crystal is replaced by contaminant ion

30
Q

nucleation vs particle size

A

further precipitation or deposition of solid phase occurs and stable solid is formed

precipitation involves nucleationand particle growth, nucleation and particle both compete

IF NUCLEATION DOMINATES: COLLOIDAL

31
Q

digestion

A

WAY TO REMOVE WATER, bonded weakly to solution

32
Q

adsorption

A

small ions are attracted and held on surface of precipitates, helps crytal growth

33
Q

reprecipitation

A

minimizing adsorbents but removes impurity, inclusion

34
Q

inclusion

A

similar sized charged particle substitutes the ion or particle of precipitates lattice

35
Q

precipitation from homogeneous

A

way to get filterable and less contaminated precipitates

36
Q

counter ion layer

A

crystallizing agent that leads to crystal formation, charge on surface develops due to adsorbed charged ions that are in excess

First layer of adsorbed ions on surface of the solid is primary adsorption layer,

surrounding, counter ion layer that balances the charge on the surface of particles,

Both form double layer which is responsible for stability of colloidal suspensions

37
Q

Stability of Colloidal Suspensions

A

electric double layer

1) adsorbed ions helps in developing charge
2) counter ion layer that balances the charge

38
Q

mother liquor

A

solution that remains after crystallization

39
Q

supersaturation

A

solution contains more solute concentration than a saturated solution

40
Q

process of supersturation

A

involves increase in solubility, make solution at high temperature

very unstable and more liable to crystallization

41
Q

How can relative supersaturation be varied during precipitate formation?

A

slow addition, gentle heating, gentle stirring, dilute solution

relationship between particle size and process

Q large= less precipitate= colloidal

to get crystalline pre, low supersaturation

Analytical Chemistry (1 decks)

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