Possible Exp. 2 Questions

Question 1

Liquids are held together by (the same, different) forces mentioned in the recrystallization lecture

Answer 1

The same

Question 2

Liquids have a (tighter, not as tight) arrangement as compared to solids

Answer 2

Not so tight

Question 3

What will happen if the attractions within a liquid are overcome?

Answer 3

The liquid will vaporize

Question 4

Define vapor pressure

Answer 4

The pressure a liquid exerts on the atmosphere surrounding it

Question 5

Define boiling point

Answer 5

When the temperature at which the vapor pressure of the liquid equals the pressure exerted upon the surface of that liquid

Question 6

What kind of pressure suppresses the liquids?

Answer 6

Atmospheric

Question 7

Energy in the form of ______ is required to increase the _______ energy and to overcome this pressure so the liquid can boil

Answer 7

Heat, kinetic

Question 8

The boiling point is used in ________.

Answer 8

Characterization

Question 9

Determining the boiling point of a liquid is (more, less) complex than recording the melting point

Answer 9

More

Question 10

Why is boiling point not as good of an indicator of purity?

Answer 10

Distillation requires more material and is affected less by impurities

Question 11

What effect do impurities have on the boiling point?

Answer 11

Impurities raise the boiling point

Question 12

A pure liquid has a (constant, changing) boiling point

Answer 12

Constant

Question 13

A changing boiling point is evidence of what?

Answer 13

Impurities

Question 14

The boiling point of a liquid is affected by what attractive forces?

Answer 14

Ionic attraction, hydrogen bonding, dipole-dipole interactions, and Van der Waals forces

Question 15

What are the internal factors that cause variations in boiling point? (Hint: There are 3)

Answer 15

Molecular weight, polarity, and shape

Question 16

Higher molecular weight=(higher, lower) boiling point

Answer 16

Higher

Question 17

Molecules with dipoles will have (higher, lower) boiling points than those of the same molecular weight that lack dipoles

Answer 17

Higher

Question 18

Molecules that can form H-bonds will boil at (higher, lower) temperatures

Answer 18

Higher

Question 19

How does shape affect boiling point?

Answer 19

Spherical molecules have lower boiling points because they do not have as many points of attraction to adjacent molecules

Question 20

What are the external factors that cause variations in the boiling points of liquids?

Answer 20

Applied pressure (usually atmospheric) and added solute

Question 21

Boiling point of most liquids (increases, decreases) about 0.5 degrees Celsius for each 10mmHg decrease in atmospheric pressure (In short, boiling point does what as pressure decreases)

Answer 21

Decrease

Question 22

The vapor pressure of the liquid will reach the pressure exerted on the surface (faster, slower) with a decrease in atmospheric pressure

Answer 22

Slower

Question 23

How does added solute cause variation in boiling point? Why?

Answer 23

Added solute raises the boiling point, because it alters the vapor pressure

Question 24

Define distillation

Answer 24

A technique for separating and purifying liquids

Question 25

Explain how a distillation works

Answer 25

A liquid is heated to boiling and the components of that liquid are separated by boiling point

Question 26

The more volatile will evaporate (first, last)

Answer 26

First

Question 27

What does volatile mean in relation to boiling point?

Answer 27

The liquid with the lower boiling point

Question 28

What is the significance of the condensing column?

Answer 28

The vapor (obtained by boiling the liquid) enters the condensing column and condenses and trickles into a collection glass

Question 29

What are the types of distillation?

Answer 29

Simple, fractional, vacuum, and micro-boiling point determination

Question 30

What is a simple distillation?

Answer 30

A way of separating two liquids with vastly different boiling points

Question 31

Define "vastly different boiling points" with regard to a simple distillation.

Answer 31

At least 40 degrees Celsius apart

Question 32

Will one have a 100% pure liquid after a single simple distillation?

Answer 32

NO. In order to get closer to 100% pure, another distillation may be necessary

Question 33

What separates fractional distillation from simple distillation?

Answer 33

Fractional distillation involves several simple distillations and uses a fractionating column to obtain theoretical plates

Question 34

What is a theoretical plate?

Answer 34

When a compound goes from the liquid to the vapor phase and back to the liquid phase. Also known as a simple distillation

Question 35

How can one control the number of theoretical plates?

Answer 35

The amount of surface area in the fractionating column. The more surface area that is available, the more theoretical plates will be performed resulting in purer products.

Question 36

What is the significance of the fractionating column?

Answer 36

The fractionating column allows multiple simple distillations to occur, and creates theoretical plates which separate the liquids once they have gone from liquid to gas and back to liquid phase

Question 37

In a fractional distillation, once the liquid starts to evaporate, more volatile liquids will push towards the (top, bottom) of the fractionating column while liquids with higher boiling points will (remain towards the bottom, move to the top)

Answer 37

Top, Remain towards the bottom

Question 38

What is vacuum distillation?

Answer 38

Vacuum distillation lowers the atmospheric pressure (or exerted pressure) to meet the vapor pressure of the liquid being distilled, causing it to vaporize

Question 39

How does vacuum distillation differ from simple or fractional distillation?

Answer 39

Vacuum distillation lowers the atmospheric pressure to meet the vapor pressure, whereas simple and fractional distillation raise the vapor pressure to meet the atmospheric pressure

Question 40

Is any heat required for a vacuum distillation?

Answer 40

No, or at least only minimal

Question 41

When is vacuum distillation useful?

Answer 41

When distilling liquids with extremely high boiling points or are particularly temperature sensitive

Question 42

What is micro-boiling point determination?

Answer 42

Used to determine the boiling point of a liquid that is small in quantity.

Question 43

What defines "small in quantity" with relation to a micro-boiling point determination?

Answer 43

<3mL of a liquid

Question 44

Micro-boiling point determination requires the use of a _______

Answer 44

Thiele Tube, or a large test tube filled with mineral oil heated around the sample

Question 45

Micro-boiling point determination yields (better, worse) results than a simple distillation

Answer 45

Worse

Question 46

How does barometric pressure affect a distillation?

Answer 46

Most distillations are done in open systems, so boiling point can be affected by barometric changes (since boiling point depends on existing air pressure)

Question 47

Define viscosity

Answer 47

The resistance of a fluid to flow

Question 48

Define an azeotrope

Answer 48

A mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition

Question 49

Azeotropes have _______ boiling points that can be either below or above the boiling points of the individual components

Answer 49

Constant

Question 50

Give an example of an azeotrope

Answer 50

Ethanol/water azeotrope; by doing more distillations, there will never be 100% ethanol, it will always stay 95% (as 95% ethanol is an azeotrope)

Question 51

What were the two reagents that were distilled?

Answer 51

Cyclohexene and methanol