EXP. 1 Flashcards
may be defined as the ratio of the
mass of a substance to the mass of an equal volume
of another substance taken as the standard.
SPECIFIC GRAVITY
For gases, the standard may be ____/_____; for
liquids and solids, it is ____.
hydrogen or air
water
True or False
The principle underlying the determination of the specific
gravity of either a liquid or a solid is the same: to find the ratio of
the mass (weight) of the substance to that of an equal density
of water
False- Density->Volume
Specific Gravity is expressed as?
Ws/Ww
is a factor that expresses how much
heavier or lighter a substance is – when compared to the
standard (water).
SPECIFIC GRAVITY
sometimes called absolute specific gravity, is
used if the masses are determined in, or referred to, a vacuum.
True specific gravity
True specific gravity is also called
Absolute Specific Gravity
the calculated result if the masses are
determined in air.
Apparent specific gravity
True or False
The difference between these specific gravities is, as a rule, very small.
True
Liquids that are lighter than
water have a specific gravity?
less than 1
those heavier
than water have a specific
gravity?
greater than 1
The common practice with regard to the determination
of specific gravity is that defined by the USP:
Unless
otherwise stated, the specific gravity basis is 25°
/25°
,
ie, the ratio of the weight of a substance in air at 25°
to
that of an equal volume of water at the same
temperature.”
is solid at 25°, the specific gravity
is determined on 100°/25° basis
Theobroma Oil
Theobroma oil, which is solid at ____°, the specific gravity
is determined on _____ basis
25
100°/25°
it is determined on a 15.56°/15.56° basis
because many years ago the US government adopted
60°F (15.56°C)
Alcohol
Alcohol, it is determined on a ______ basis
because many years ago the US government adopted
______ as the temperature at which
_____measurements are to be made for
government control of alcoholic liquids.
15.56°/15.56°
60°F (15.56°C)
alcoholometric
is a glass flask with a close-
fitting ground glass stopper with a capillary
hole through it.
PYCNOMETER
A pycnometer is a special glass bottle used to determine specific gravity.
Generally available for laboratory use in volumes ranging from _____.
1 mL to 50 mL
The Westphal Balance was first described
by German chemist _____
in _____
Carl Friedrich Mohr 1832
Westphal Balance:
Modifications were made by the good _____ who replaced a _____
with an _____.
Dr.
Westphal
tray method
adjustable arm counterweight
Westphal Balance is A.K.A.
Mohr Westphal Balance
A direct-reading instrument for
determining the densities of solids
and liquids; a _____ of known
mass is immersed in the liquid whose
density is to be measured.
Westphal Balance
plummet
WESTPHAL BALANCE relies on______ and
is balanced by an array of horseshoe-shaped
______ which come in _____,____,_____,_____ masses.
Archimedes’ Principle of buoyancy
counterweights/riders
5 g, 0.5 g, 0.05 g, and 0.005
g
respectively signify the ones place of the specific gravity
of the sample solution, the tenths place, the hundredths
place, and the thousandths place.
counterweights (sometimes called riders)
The numerical value each rider represents is equal to the
numbered ______ which it sits in when the scale
is balanced.
notch of the arm
True or False
The Westphal Balance is capable of highly
accurate density readings
False- capable->incapable
For extremely accurate density readings one may
prefer to use a _____ although for speed
and ease of use a _____ can quickly provide a
very close approximation to the true density of
any liquid solution.
pycnometer & Westphal
is an instrument used for
determining the specific gravity of liquids.
hydrometer
is usually made of glass and
consists of a cylindrical stem and a bulb
weighted with mercury or lead shot to
make it float upright.
hydrometer
Parts of the Westphal Balance:
- Balance Beam
- Transverse notch scale
- Stationary counterweight
- Balance indicator scale
- Glass float
- Riders
- Vessel with liquid
- Thermometer
- Double Pan
9.a. Upper Pan (solid brass)
9.b. Lower Pan (glass or aluminum w/ openings)
The function of the hydrometer is based on
Archimedes’ principle
Thus, the lower the density of the substance,
the _____ the hydrometer will sink.
lower
Hydrometers can be divided into two general classes:
liquids heavier than water and liquids lighter than water
In the standard hydrometer scale, known as the specific
gravity scale, distilled water equals ______, the initial point of
measurement.
1.000
Liquids lighter than water are scaled ____ 1.000 specific
gravity, and liquids heavier than water are scaled _____
1.000 specific gravity.
below; above
for
liquids heavier than water.
Heavy Hydrometer
liquids
lighter than water.
Light Hydrometer
