MIDTERM - Extraction, Sublimation, and Melting Point Determination Flashcards
two methods of chemical analysis:
qualitative and quantitative
- involves the determination of the
chemical composition of a sample. - It encompasses a set of analytical chemistry techniques to provide nonnumerical information about a specimen.
- can tell you whether an atom, ion, functional group, or compound is present or absent in a sample, but it does not provide information about its quantity.
qualitative analysis
Quantification of a sample, in contrast, is called
quantitative analysis
typically measures changes in, but not limited to:
- color, melting point, odor, reactivity, radioactivity, boiling point, bubble production, and precipitation.
Methods include, but not limited to:
- distillation, extraction, precipitation, chromatography, and spectroscopy.
qualitative analysis
random error
human error
eg. a researcher misreading a weighing scale records an incorrect measurement
systematic error
machine error
eg. a miscalibrated scale consistently registers weights as higher than they actually are
gross errors
Gross errors are errors that are so serious (i.e. large in magnitude) that they cannot be attributed to either systematic or random errors associated with the sample, instrument, or procedure.
eg. writing down a value of 100 when the reading was actually 1.00.
Caffeine is a member of the class of
compounds called
alkaloids
nitrogen-containing basic compounds that are found in plants.
They usually taste bitter and often are
physiologically active in humans.
alkaloids
Caffeine acts as a ________. It is physically addictive.
stimulant
It is the most widely used βlegalβ stimulant, rivaled by its sister molecule, ____________, which is found in the cacao bean (and
chocolate).
Both of these molecules have the parent purine ring structure, which is also seen in guanine and adenine (found in
DNA and RNA).
THEOBROMINE
The other components aside from caffeine in tea leaves include _______ and classes of compounds called
cellulose
tannins, flavins, and chlorophylls
the physical process by which a compound (or mixture of compounds) is transferred from one phase to another.
extraction
Water-soluble components in the tea leaves or coffee beans are being transferred from a solid phase, the leaves or beans, into a liquid phase, the hot water.
This is an example of
solid-liquid extraction
In the extraction experiment, we make use of ORGANIC SOLVENT to extract the organic components, namely caffeine, from tea.
This process is known as
liquid-liquid extraction
The physical process that rules liquid-liquid extraction is known as ________________, or the distribution of solutes between a pair of solvents.
solvent-solvent partitioning
Organic solvents such as diethyl ether, toluene, and methylene chloride (dichloromethane, DCM) have a very limited solubility in water.
These solvents are _________ with water.
immiscible
For example, if DCM is mixed with water, a two-layer system is obtained. The upper layer contains the less-dense solvent (water, density = ππ/πππ) and the lower layer is the more-dense solvent (DCM, density = π.πππ/πππ).
The water layer along with its components is called the _____________.
The DCM layer along with its components is called the _____________.
aqueous phase
organic phase
The tendency of a solute (in this case, caffeine) to dissolve preferentially in one solvent over another can be represented in a
partition (distribution) coefficient, π²π .
If π²π« >π, solute prefers the
organic phase
If π²π« < π, the solute prefers the
aqueous phase
Suppose solute A is added to a mixture of water and DCM. The system is shaken and attains equilibrium. Solute A will be present in both layers, but larger amounts of it will be in the solvent for which it has a higher affinity.
The distribution between both solvents is dictated by the _____________, of A between the two solvents.
partition coefficient π²π
- measures the efficiency of the extraction.
Increasing the volume of organic solvent increases the percent recovery as more solute is extracted into the larger organic phase.
percentage recovery
It is standard to perform ____ organic
extractions of caffeine.
THREE
The tea is made under basic conditions to ionize mildly acidic flavonoids and tannins, causing them to be more ___________.
In the liquid-liquid (DCM-water) extraction, caffeine will be separated from the water-soluble pigments. After removing trace amounts of water, the low-boiling solvent is evaporated to yield the crude organic extracts.
Further purification by ________ results in white crystals of caffeine.
water-soluble
sublimation
- What is the role of sodium
carbonate, π΅πππͺπΆπ, in the
extraction of caffeine from tea
leaves?
NEUTRALIZES ACIDS
- It prevents caffeine from becoming protonated (positively charged) by any acidic components in the tea leaves. This ensures caffeine stays soluble in the organic solvent used later.
PRECIPITATES TANNINS
- It reacts with tannins, turning them into sodium salts that are insoluble in the organic solvent used for caffeine extraction. This prevents unwanted tannins from being extracted alongside caffeine.
- Which is more efficient, single
extraction or multiple
extraction? Why?
Multiple extraction is more efficient than single extraction for caffeine.
In a single pass, some caffeine remains trapped within the tea leaves. Multiple extractions with fresh solvent allow for more complete removal of caffeine.
- What is the role of anhydrous sodium sulfate in extraction?
Anhydrous sodium sulfate acts as a drying agent in caffeine extraction from tea leaves.
It removes residual water from the organic solvent layer containing the caffeine.
This ensures the extracted caffeine is purer and easier to handle later.
the transition of a solid into a gas
without passing through the intermediary liquid stage.
This normally occurs when the vapor pressure of a substance is GREATER than the atmospheric pressure.
It is a process used in the purification of substances that have non-volatile impurities or substances that have a significantly lower vapor pressure than a pure compound.
sublimation
the temperature at which a solid is
changed into a liquid.
happens when the solid phase of a substance and its liquid phase are in a
dynamic equilibrium.
can be used to determine its purity
melting point of a pure substance is fixed while an impure substance melts over a wide range of higher temperature and a lower temperature.
melting point
a white crystalline powder and is the simplest of aromatic carboxylic acids.
It has a melting point of πππ Β°πͺ and a boiling point of πππ Β°πͺ.
It is commonly used as a food preservative and a germicide or antifungal agent.
benzoic acid
