CHM 205 LAB FINAL REVIEW
What is the purpose of using a fluted cone? - Answer Creates higher surface area,
allowing for faster filtration
Which is the most efficient technique to remove solids from microscale solutions? -
Answer use a filter pipette with a small piece of cotton and filter the solution into a craig
tube.
What is the correct way to hold a pipette and why? - Answer Vertical, the liquid must not
touch the sides and this prevents a change in the sample volume from occurring.
Types of melting point tests - Answer slow run
fast run
mixed melting point: mix your unknown with you known and report the range
melting point range - Answer refers to the range of the temperatures in which a solid will
melt and it can be used to establish the purity of a compound. Pure compounds will
exhibit narrow melting point ranges and higher melting points.
dissolution vs melting point definition - Answer dissolution is the process of when a
gaseous, solid, or liquid phase dissolves in a solvent to form a solution. melting point is
the process of a solid turning into a liquid, phase change occurs
proper heating rate - Answer The proper heating rateis 1-2 C/min. If the rate is
exceeded, you may risk having an inaccurate melting point range.
average number of drops in 1 mL - Answer 28 drops/mL
why is preheated filter paper used in hot gravity filtration - Answer to prevent the
solution from immediately recrystallizing as it hit the cold filter paper.
how is sand (inorganic) material removed? - Answer The solution is filtered leaving only
the sand on the filter paper.
how is colored organic material removed? - Answer Activated charcoal is added to the
solution which absorbs the contaminants and then it is filtered.
how is very soluble material removed? - Answer A very soluble contaminant will remain
in the solution when the recrystallization solution is filtered (vaccuum filtration).
Why is acetone used in the lab? - Answer Acetone is a good solvent for cleaning
glassware due to it being water soluble and having low surface tension which allows it
to clean the surface without forming droplets. Low surface tension also allows the
solvent to dissolve contaminants easily.
, What do boiling chips do? - Answer they prevent bumping and local overheating
liquid-liquid extraction - Answer used for the separation of compounds comprising a
sample mixture with two immiscible solvents.
Immiscible solvents definition - Answer Immiscible solvents are solvents that do not
from a homogenous mixture when they are mixed. form two distinct layers
why is a drying agent used in liquid-liquid extraction? - Answer To remove trace amount
of water, added in small amounts at a time.
ratio of concentration of a solute in each layer is defined by... - Answer the partion
coefficient K=C2/C1
in the biphasic layer of the solution which one usually rests at the top - Answer the
organic solvent, less dense than water
What is used to spot TLC plates - Answer capillary tubes
why should spots be small on the TLC plates - Answer big spots will produce blurry and
indistinct lines
how to remedy a streak on a TLC spot - Answer add a few drops of ammonia or
carboxylic acid.
What happens to the TLC plate in the iodine jar - Answer iodine reacts with the plate
forming brownish yellowish complexes
retardation factor defined - Answer The ratio of the distance the compound travels to the
total distance the solvent travels. distance traveled/ total distance
What is the purpose of the wick/ filter paper - Answer creates an atmosphere saturated
with the solvent, helps stabilize the plate, and speeds up the process of the
development of the plate.
Polarity of compounds on a TLC plate - Answer Polar Compounds: travel up TLC plate
slowly and have a lower Rf value
Non-polar Compounds: travel up TLC plate fast and have a higher Rf value.
Polarity in TLC - Answer More polar=more intermolecular interactions
Less polar=less intermolecular interaction
What is the direction of motion of mobile phase in column chromatography? - Answer
down through the column
What is the purpose of using a fluted cone? - Answer Creates higher surface area,
allowing for faster filtration
Which is the most efficient technique to remove solids from microscale solutions? -
Answer use a filter pipette with a small piece of cotton and filter the solution into a craig
tube.
What is the correct way to hold a pipette and why? - Answer Vertical, the liquid must not
touch the sides and this prevents a change in the sample volume from occurring.
Types of melting point tests - Answer slow run
fast run
mixed melting point: mix your unknown with you known and report the range
melting point range - Answer refers to the range of the temperatures in which a solid will
melt and it can be used to establish the purity of a compound. Pure compounds will
exhibit narrow melting point ranges and higher melting points.
dissolution vs melting point definition - Answer dissolution is the process of when a
gaseous, solid, or liquid phase dissolves in a solvent to form a solution. melting point is
the process of a solid turning into a liquid, phase change occurs
proper heating rate - Answer The proper heating rateis 1-2 C/min. If the rate is
exceeded, you may risk having an inaccurate melting point range.
average number of drops in 1 mL - Answer 28 drops/mL
why is preheated filter paper used in hot gravity filtration - Answer to prevent the
solution from immediately recrystallizing as it hit the cold filter paper.
how is sand (inorganic) material removed? - Answer The solution is filtered leaving only
the sand on the filter paper.
how is colored organic material removed? - Answer Activated charcoal is added to the
solution which absorbs the contaminants and then it is filtered.
how is very soluble material removed? - Answer A very soluble contaminant will remain
in the solution when the recrystallization solution is filtered (vaccuum filtration).
Why is acetone used in the lab? - Answer Acetone is a good solvent for cleaning
glassware due to it being water soluble and having low surface tension which allows it
to clean the surface without forming droplets. Low surface tension also allows the
solvent to dissolve contaminants easily.
, What do boiling chips do? - Answer they prevent bumping and local overheating
liquid-liquid extraction - Answer used for the separation of compounds comprising a
sample mixture with two immiscible solvents.
Immiscible solvents definition - Answer Immiscible solvents are solvents that do not
from a homogenous mixture when they are mixed. form two distinct layers
why is a drying agent used in liquid-liquid extraction? - Answer To remove trace amount
of water, added in small amounts at a time.
ratio of concentration of a solute in each layer is defined by... - Answer the partion
coefficient K=C2/C1
in the biphasic layer of the solution which one usually rests at the top - Answer the
organic solvent, less dense than water
What is used to spot TLC plates - Answer capillary tubes
why should spots be small on the TLC plates - Answer big spots will produce blurry and
indistinct lines
how to remedy a streak on a TLC spot - Answer add a few drops of ammonia or
carboxylic acid.
What happens to the TLC plate in the iodine jar - Answer iodine reacts with the plate
forming brownish yellowish complexes
retardation factor defined - Answer The ratio of the distance the compound travels to the
total distance the solvent travels. distance traveled/ total distance
What is the purpose of the wick/ filter paper - Answer creates an atmosphere saturated
with the solvent, helps stabilize the plate, and speeds up the process of the
development of the plate.
Polarity of compounds on a TLC plate - Answer Polar Compounds: travel up TLC plate
slowly and have a lower Rf value
Non-polar Compounds: travel up TLC plate fast and have a higher Rf value.
Polarity in TLC - Answer More polar=more intermolecular interactions
Less polar=less intermolecular interaction
What is the direction of motion of mobile phase in column chromatography? - Answer
down through the column
