Chapter 34: Preparing Samples for Analysis

Question 1

TRUE or FASE
Crushing and grinding the sample often changes its composition

Answer 1

TRUE

Question 2

Crushing and grinding is usually required to

Answer 2

decrease the particle size of solid samples

Question 3

Benefits of grinding

Answer 3

increases the surface area of the solid
increases its susceptibility to reaction with atmosphere

Question 4

TRUE or FALSE
Crushing and grinding must be continued until the entire sample passes through a screen of the desired mesh size.

Answer 4

TRUE

Question 5

TRUE or FALSE
Mechanical abrasion of the surfaces of the grinding device can contaminate the sample

Answer 5

TRUE

Question 6

a useful device for grinding solids that are not too hard and is used for medium-sized samples and particles

Answer 6

Ball mill

Question 7

Tools for reducing the size of solid samples

Answer 7

ball mill
mixer/ mill
Platter diamond mortar

Question 8

is used for crushing hard, brittle materials

Answer 8

Platter diamond mortar

Question 9

forms an integral part of the molecular or crystalline structure of a compound in its solid state.

Answer 9

essential water

Question 10

is water that is formed when a pure solid is decomposed by heat or other
chemical treatment.

Answer 10

water of constitution

Question 11

is the water that is physically retained by a solid.

Answer 11

nonessential water

Question 12

is a type of nonessential water that is retained on the surface of
solids, which are dependent on humidity, temperature, and the specific surface area of the solid

Answer 12

adsorbed water

Question 13

TRUE or FALSE
Adsorption of water occurs to some degree on all solids.

Answer 13

TRUE

Question 14

is encountered with many colloidal substances, such as starch, protein, charcoal, zeolite minerals, and silica gel. It is also defined as contained within the interstices of the molecular structure of a colloidal compound

Answer 14

sorbed water

Question 15

types of nonessential water

Answer 15

adsorbed
sorbed
occluded

Question 16

TRUE or FALSE
In contrast to adsorbed water, the quantity of sorbed water is often large,
amounting to as not as much as 20% or more of the total mass of the solid

Answer 16

FALSE
In contrast to adsorbed water, the quantity of sorbed water is often large, amounting to as much as 20% or more of the total mass of the solid

Question 17

liquid water entrapped
in microscopic pockets spaced irregularly throughout solid crystals

Answer 17

occluded

Question 18

is the ratio of the
vapor pressure of water in the atmosphere
to its vapor pressure in air that
is saturated with moisture

Answer 18

relative humidity

Question 19

TRUE or FALSE
The essential water content of a compound depends on the temperature and relative humidity of its surroundings

Answer 19

TRUE

Question 20

example of types of essential water

Answer 20

CaC2O4 . 2H2O
BaCl2 . 2H2O

Question 21

second type of essential water and is found in compounds that yield stoichiometric amounts of water when heated or otherwise decomposed. Example of which is found in the heating process of KHSO4 such that when heated gives the following chemical reaction
2KHSO4–> K2S2O7 +H2O

Answer 21

water of constitution

Question 22

TRUE or FALSE
the composition of a sample containing essential water depends greatly on the relative humidity of its environment.

Answer 22

TRUE

Question 23

TRUE or FALSE
The amount of water adsorbed on a solid decreases as the temperature of the solid increases and generally approaches zero when the solid is heated above 100°C.

Answer 23

TRUE

Question 24

TRUE or FALSE
Adsorption or desorption of moisture usually occurs rapidly, with equilibrium often being reached after an hour. The speed of the process is often observable during the weighing of finely divided anhydrous solids, where a continuous increase in mass will occur unless the solid is contained in a tightly stoppered vessel.

Answer 24

FALSE
5 to 10 min

Question 25

TRUE or FALSE the sorption process may require days or even weeks to attain equilibrium, particularly at room temperature.

Answer 25

TRUE

Question 26

is not in equilibrium with the atmosphere and, therefore, is insensitive to changes in humidity.

Answer 26

occluded water

Question 27

is a process in which a crystalline material containing occluded water explodes during heating because of a buildup in internal pressure resulting from steam formation.

Answer 27

decrepitation

Question 28

TRUE or FALSE Heating a solid containing occluded water may cause a gradual diffusion of the moisture to the surface, where it evaporates

Answer 28

TRUE