chem 116 quiz 3

Question 1

when a solute is added to a liquid, the freezing point of the resulting solution is ? this is known as ?

Answer 1

lower than the freezing point of the pure liquid; freezing point depression

Question 2

freezing point depression can be calculated by the equation

Answer 2

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)

Question 3

Kf depends on

Answer 3

the solvent, not the solute

Question 4

when is lowering the freezing point of a solvent useful?

Answer 4

salting roads during the winter

Question 5

solution properties are defined as colligative if

Answer 5

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

Question 6

list some colligative properties

Answer 6

boiling point, vapor pressure, osmotic pressure, freezing point

Question 7

the larger the ratio of particles of solute to solvent, the ? the deviation will be from that of the pure solvent

Answer 7

greater

Question 8

with the addition of a solute, the boiling point will?, the vapor pressure and osmotic pressure ?, and the freezing point ?

Answer 8

boiling point - elevated
VP and OP - decreased
FP - depressed

Question 9

the Van’t Hoff factor (i) is used in calculations to account for

Answer 9

the number of particles contributed to a solution by a solute

Question 10

the concentration unit used in the calculation of freezing point depression is

Answer 10

molality

Question 11

why use molality instead of molarity for FP depression calculations?

Answer 11

molality is independent of temperature effects on the density of the solution

Question 12

in this lab, you will determine the freezing point depression constant, Kf, of a solvent by

Answer 12

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

Question 13

moles solute =

Answer 13

solute mass / molar mass

Question 14

molality is

Answer 14

moles solute / kg solvent

Question 15

mole mass =

Answer 15

(i * Kf * solute mass) / (delta T * kg solvent)

Question 16

hexane has

Answer 16

a strong odor

Question 17

with naphthalene, hexane, and the unknown compound, you should

Answer 17

avoid eye and skin contact

Question 18

because organic chemicals are often flammable, we will use

Answer 18

NO FLAMES - hot plates only (don’t get burned on the hot plate or the water or its container)

Question 19

dispose of naphthalene in

Answer 19

the solid waste bin

Question 20

excess unknown and hexane can be disposed of by being

Answer 20

poured into the waste bottle

Question 21

naphthalene synonym

Answer 21

moth balls; white tar; moth flakes

Question 22

hexane synonym

Answer 22

normal hexane; n-Hexane

Question 23

what to do to prevent coming into contact with hexane

Answer 23

vents; safety goggles; lab attire; impervious gloves

Question 24

what to do to prevent coming into contact with naphthalene

Answer 24

keep away from heat or flame; do not ingest; avoid contact with eyes; lab attire; ventilation; gloves

Question 25

what to do if you come into contact with hexane

Answer 25

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

Question 26

what to do if you come into contact with naphthalene

Answer 26

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

Question 27

to determine the melting point of a substance,

Answer 27

heat it and record the temperature at which you first begin seeing evidence of liquid; melting point should equal the freezing point?