Chapter 34: Preparing Samples for Analysis Flashcards
TRUE or FASE
Crushing and grinding the sample often changes its composition
TRUE
Crushing and grinding is usually required to
decrease the particle size of solid samples
Benefits of grinding
increases the surface area of the solid
increases its susceptibility to reaction with atmosphere
TRUE or FALSE
Crushing and grinding must be continued until the entire sample passes through a screen of the desired mesh size.
TRUE
TRUE or FALSE
Mechanical abrasion of the surfaces of the grinding device can contaminate the sample
TRUE
a useful device for grinding solids that are not too hard and is used for medium-sized samples and particles
Ball mill
Tools for reducing the size of solid samples
ball mill
mixer/ mill
Platter diamond mortar
is used for crushing hard, brittle materials
Platter diamond mortar
forms an integral part of the molecular or crystalline structure of a compound in its solid state.
essential water
is water that is formed when a pure solid is decomposed by heat or other
chemical treatment.
water of constitution
is the water that is physically retained by a solid.
nonessential water
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
adsorbed water
TRUE or FALSE
Adsorption of water occurs to some degree on all solids.
TRUE
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
sorbed water
types of nonessential water
adsorbed
sorbed
occluded
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
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
liquid water entrapped
in microscopic pockets spaced irregularly throughout solid crystals
occluded
is the ratio of the
vapor pressure of water in the atmosphere
to its vapor pressure in air that
is saturated with moisture
relative humidity
TRUE or FALSE
The essential water content of a compound depends on the temperature and relative humidity of its surroundings
TRUE
example of types of essential water
CaC2O4 . 2H2O
BaCl2 . 2H2O
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
water of constitution
TRUE or FALSE
the composition of a sample containing essential water depends greatly on the relative humidity of its environment.
TRUE
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.
TRUE
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.
FALSE
5 to 10 min
TRUE or FALSE
the sorption process may require days or even weeks to attain equilibrium, particularly at room temperature.
TRUE
is not in equilibrium with the atmosphere and, therefore, is insensitive to changes in humidity.
occluded water
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.
decrepitation
TRUE or FALSE
Heating a solid containing occluded water may cause a gradual diffusion of the moisture to the surface, where it evaporates
TRUE
