Lesson 7: Precipitation and Volatilizatio Gravimetry

Question 1

A substance that is dissolved in a solution

Answer 1

Solute

Question 2

the liquid in which asoluteisdissolvedto form a solution.

Answer 2

Solvent

Question 3

a solution that contains less than the maximum amount of solute that is capable of being dissolved

Answer 3

Unsaturated Solution

Question 4

a solution that has dissolved as much solute as it is capable of dissolving

Answer 4

Saturated Solution

Question 5

interaction between solute and solution that forms ionic bond or precipitate

Answer 5

Precipitate Forms

Question 6

a solution that contains more than the maximum amount of solute that is capable of being dissolved at a given temperature.

Answer 6

Supersaturated Solution

Question 7

an Unstable solution that contains a higher solute concentration than a saturated solution

Answer 7

supersaturated solution

Question 8

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

It is based on mass measurements with an analytical balance

Answer 8

Gravimetric Methods

Question 9

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.

Answer 9

Precipitation Gravimetry

Question 10

the method in which the analyte is converted to a soluble precipitate

Answer 10

Precipitation Gravimetry

Question 11

can be obtained by filtering, washing free of impurities, converting to a product of known composition by suitable heat treatment, and weighing.

Answer 11

precipitate

Question 12

What are the 4 properties of precipitating agents

Answer 12

(1) easily filtered and can be washed free of contaminants
(2) of sufficiently low solubility that no significant loss of the analyte occurs during filtration and washing;
(3) Chemical inert or is unreactive with the constituents of the open atmosphere;
(4) Composition can be determined with high confidence after it was dried or ignited.

Question 12

a few ions, atoms, or molecules (around four or five) come together to form a stable solid. Often, these nuclei form on the surface of suspended solid contaminants, such as dust particles.

Answer 12

Nucleation

Question 13

two ways at which precipitates are formed

Answer 13

Nucleation and particle growth

Question 14

If predominates, a precipitate containing a large number of small particles results

Answer 14

nucleation

Question 15

if predominates, a smaller number of larger particles is produced.

Answer 15

particle growth

Question 15

competition between additional nucleation and growth of existing nuclei

Answer 15

particle growth

Question 16

minimum number of atoms, ions, or molecules join together to give a stable solid

Answer 16

Nucleation

Question 17

As excess solute precipitates with time, supersaturation decreases to zero

Answer 17

supersaturated solution

Question 18

coagulation of colloids can be hastened by what methods?

Answer 18

1. Heating
2. continuously stirring
3. by adding an electrolyte into the mixture that will act as a medium

Question 19

What is the reason for the stability of colloidal particles?

Answer 19

its particles are either positively or negatively charged and thus repel one another.

Question 20

a process in which a substance (gas, liquid, or solid) is held on the surface of a solid.

Answer 20

adsorption

Question 21

retention of a substance within the pores of a solid.

Answer 21

absorption

Question 22

random movement of solute in solution

Answer 22

Brownian Motion

Question 23

Positive charge

Answer 23

Cation

Question 24

negative charge

Answer 24

Anion

Question 25

happens when colloids are washed, because during washing, some of the electrolytes responsible for keeping the coagulated form are leached from the internal liquid in contact with the solid particles.

Answer 25

Peptization

Question 26

process by which a coagulated colloid reverts to its original dispersed state.

Answer 26

Peptization

Question 27

How to prevent the the effect of increasing the volume of the counter-ion layer in peptization?

Answer 27

solvent that can easily volatilize is used for washing, so that during the drying step, this solvent is removed from the precipitates.

Question 27

What happens when electrolyte is removed in Peptization?

Answer 27

has the effect of increasing the volume of the counter-ion layer.

Question 28

are particles with diameters ranging from order of tenths of a millimeter or greater.

Answer 28

crystalline suspension

Question 28

of which the particles are too small (10-7 to 10-4( in diameter) that they are invisible to the naked eye.

Answer 28

colloidal suspensions

Question 29

suspended within the mixture, they show no tendency to settle thus making them difficult to filter

Answer 29

colloidal suspensions

Question 30

The particles of a crystalline suspension tend to settle spontaneously and are easily filtered.

Answer 30

crystalline suspension

Question 31

the phenomenon in which the particles in a colloid scatter the beams of light that are directed at them

Answer 31

Tyndall effect

Question 31

Factors That Determine the Particle Size of Precipitates

Answer 31

Precipitate Solubility Temperature Reactant Concentrations Rate At Which Reactants Are Mixed

Question 32

equation for relative supersaturation

Answer 32

Q-S / S

Question 33

What is meant by Q in the formula of relative supersaturation?

Answer 33

the concentration of the solute

Question 34

What is meant by S in the formula of relative supersaturation?

Answer 34

the equilibrium solubility

Question 35

if (q-s/s) is large, the precipitates will tend to be _____?

Answer 35

colloidal

Question 35

when (q-s/s) is small, then we can expect that the precipitates will be____?

Answer 35

crystalline in nature

Question 36

How to improved the particle size of a crystalline solid?

Answer 36

by minimizing Q or maximizing S, or both in equation.

Question 37

How to minimize Q the particle size of a crystalline solid ?

Answer 37

diluting the solution and adding the suitable precipitating agent slowly accompanied by good mixing should be done.

Question 38

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

Answer 38

Digestion

Question 39

How to maximize S the particle size of a crystalline solid?

Answer 39

S is increased by precipitating from hot solution or by adjusting the pH of the precipitation medium.

Question 40

the solution from which a precipitate was formed

Answer 40

Mother liquor

Question 41

a normally soluble compound is carried out of solution on the surface of a coagulated colloid.

Answer 41

Surface Adsorption

Question 42

often the major source of contaminants in coagulated colloids but this problem doesn’t arise on crystalline precipitates.

Answer 42

Adsorption

Question 42

Explain how digestion improved the purity of many coagulated colloids.

Answer 42

water is expelled from the solid to give a denser mass that has a smaller specific surface area for adsorption

Question 43

How to improved the purity of many coagulated colloids?

Answer 43

Digestion

Question 43

This compound consists of the primarily adsorbed ion and an ion of opposite charge from the counter-ion layer.

Answer 43

Surface Adsorption

Question 44

the filtered solid is re-dissolved and reprecipitated

Answer 44

Reprecipitation

Question 45

water is expelled from the solid to give a denser mass that has a smaller specific surface area for adsorption.

Answer 45

Reprecipitation

Question 46

contaminant ions replace an ion in the lattice of a crystal

Answer 46

mixed crystal formation

Question 46

adds substantially to the time required for an analysis.

Answer 46

Reprecipitation

Question 47

Requirement for the exchange in Mixed-Crystal Formation

Answer 47

ions should have the same charge and their ionic sizes should differ in not more than 5%.

Question 48

When a crystal is growing rapidly during precipitate formation, foreign ions in the counter-ion layer may become trapped, or occluded, within the growing crystal.

Answer 48

Occlusion

Question 49

occurs when crystals lie close together during growth. Several crystals grow together and in so doing trap a portion of the solution in a tiny pocket.

Answer 49

Mechanical entrapment

Question 50

are at a minimum when the rate of precipitate formation is low, that is, under conditions of low supersaturation

Answer 50

occlusion and mechanical entrapment

Question 51

There are four types of coprecipitation:

Answer 51

1. surface adsorption, 2. mechanical entrapment, 3. occlusion 4. mixed-crystal formation

Question 52

a reaction that involves the simultaneous occurrence of nucleation, growth, coarsening, and/or agglomeration processes.

Answer 52

Coprecipitation

Question 52

a type of coprecipitation in which a compound is trapped within a pocket formed during rapid crystal growth.

Answer 52

Occlusion

Question 53

a process in which normally soluble compounds are carried out of solution by a precipitate

Answer 53

Coprecipitation

Question 54

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

Answer 54

Homogeneous precipitation

Question 54

Two types of Gravimetric Analysis 

Answer 54

Precipitation Method and Volatilisation method

Question 55

may occur in both colloidal and crystalline precipitates, but occlusion and mechanical entrapment are confined to crystalline precipitates.

Answer 55

Mixed-crystal formation

Question 56

nvolve the generation of a precipitating agent from a chemical reaction carried out slowly.

Answer 56

Precipitation in homogeneous solutions

Question 57

are better suited for analysis than a solid formed by direct addition of a precipitating reagent.

Answer 57

both colloidal and crystalline

Question 58

analysis of an ion by measuring mass of a precipitate formed from the ion 

Answer 58

Precipitation Method

Question 59

measuring mass before and after heating and removal of a volatile substance 

Answer 59

Volatilisation method