chem 116 quiz 3 Flashcards
when a solute is added to a liquid, the freezing point of the resulting solution is ? this is known as ?
lower than the freezing point of the pure liquid; freezing point depression
freezing point depression can be calculated by the equation
delta T = i m Kf
(delta T is freezing point depression, i is the Van’t Hoff factor, m is molality, and Kf is the freezing point depression constant)
Kf depends on
the solvent, not the solute
when is lowering the freezing point of a solvent useful?
salting roads during the winter
solution properties are defined as colligative if
the property depends only on the ratio of the number of particles of solute and solvent in the solution, not the identity of the solute
list some colligative properties
boiling point, vapor pressure, osmotic pressure, freezing point
the larger the ratio of particles of solute to solvent, the ? the deviation will be from that of the pure solvent
greater
with the addition of a solute, the boiling point will?, the vapor pressure and osmotic pressure ?, and the freezing point ?
boiling point - elevated
VP and OP - decreased
FP - depressed
the Van’t Hoff factor (i) is used in calculations to account for
the number of particles contributed to a solution by a solute
the concentration unit used in the calculation of freezing point depression is
molality
why use molality instead of molarity for FP depression calculations?
molality is independent of temperature effects on the density of the solution
in this lab, you will determine the freezing point depression constant, Kf, of a solvent by
adding a measured amount of a known impurity (solute)
you can calculate Kf because you can measure the change in temperature and calculate the concentration
moles solute =
solute mass / molar mass
molality is
moles solute / kg solvent
mole mass =
(i * Kf * solute mass) / (delta T * kg solvent)
hexane has
a strong odor
with naphthalene, hexane, and the unknown compound, you should
avoid eye and skin contact
because organic chemicals are often flammable, we will use
NO FLAMES - hot plates only (don’t get burned on the hot plate or the water or its container)
dispose of naphthalene in
the solid waste bin
excess unknown and hexane can be disposed of by being
poured into the waste bottle
naphthalene synonym
moth balls; white tar; moth flakes
hexane synonym
normal hexane; n-Hexane
what to do to prevent coming into contact with hexane
vents; safety goggles; lab attire; impervious gloves
what to do to prevent coming into contact with naphthalene
keep away from heat or flame; do not ingest; avoid contact with eyes; lab attire; ventilation; gloves
what to do if you come into contact with hexane
eye contact: flush eyes with running water for at least 15 minutes
skin contact: wash with soap and water; cover the irritated skin with an emollient
serious skin contact: wash with a disinfectant soap and cover the contaminated skin with an anti-bacterial cream; seek medical attention
inhalation: remove to fresh air; get oxygen or artificial breathing
ingestion: do not induce vomiting; loosen tight clothing
what to do if you come into contact with naphthalene
eye contact: flush eyes with running water for at least 15 minutes
skin contact: wash with plenty of water; cover irritated skin with emollient
inhalation: rest in a well ventilated area
ingestion: do not induce vomiting; loosen tight clothing
to determine the melting point of a substance,
heat it and record the temperature at which you first begin seeing evidence of liquid; melting point should equal the freezing point?
