10.2 Properties of Liquids

10.2 Properties of Liquids

​Presenter

​

​Dr. Luis Bello

​

​Online Textbook:

​

​https://openstax.org/books/chemistry-2e/pages/10-2-properties-of-liquids

Previous: 10.1 Intermolecular Forces

Types of intermolecular forces possible between atoms or molecules in condensed phases (dispersion forces, dipole-dipole attractions, and hydrogen bonding)

Types of intermolecular forces experienced by specific molecules based on their structures

Relation between the intermolecular forces present within a substance and the temperatures associated with changes in its physical state.

Classroom Resources | Intermolecular Forces | AACT

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Multiple Choice

Which of the following factors plays an important role in the identification of specific intermolecular forces in a molecule?

• bond type

• density

• solubility

• molecular polarity

Multiple Choice

Which of the following molecules contains only London dispersion forces?

• CF₄

• HCl

• H₂O

• MgO_(aq)

Multiple Choice

Which of the following molecules would have the lowest boiling point?

• CH₄

• C₂H₆

• C₃H₈

• C₄H₁₀

Multiple Choice

Propane is a gas at STP, while bromine is a liquid at STP. Which statement correctly explains these observations?

• Bromine has weaker intermolecular forces than propane does

• Bromine has greater molecular polarity than propane does

• Bromine has weaker molecular polarity than propane does

• Bromine has stronger intermolecular forces than propane does

Multiple Choice

Which of the following molecules has hydrogen bonding?

• HCl

• HI

• HF

• HBr

Multiple Choice

Which of the following statements correctly compares the behavior of a mixture of ethanol and water at STP?

• Water will evaporate first, because it has weaker intermolecular forces

• Ethanol will evaporate first, because it has weaker intermolecular forces

• Ethanol and water will evaporate simultaneously

• The aqueous solution will evaporate partially at a temperature between the boiling points of water and of ethanol

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​The Structure and Properties of Water

​

​Key Points

• Water is a liquid at standard temperature and pressure (25 degrees Celsius and 1 atm, for liquids).

• Water is is tasteless and odorless.

• Water is transparent in the visible part of the electromagnetic spectrum.

• Water can act as either an acid or a base.

• Water is a universal solvent, dissolving many substances found in nature.

​Surface Tension

​Key Points

• ​Surface tension is a fundamental property of the surface of the liquid.

• ​Surface tension is responsible for the curvature of the surfaces of air and liquids.

• ​Surface tension is responsible for the ability of some solid objects to “float” on the surface of a liquid.

​Surface tension is responsible for the shape of the interface between two immiscible liquids.

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​​The surface tensions of a few common liquids and solutions are as follows, in dyne/cm (note the particularly high surface tension of the water):

• ​water, H(OH): 72.7

• ​benzene, C₆H₆: 40.0

• ​glycerin, C₃H₂(OH)₃: 63.0

• ​sucrose solution (85% in water): 76.4

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​Viscosity

Viscosity is a measure of a fluid’s resistance to flow.

​Key Points

• A fluid’s resistance to flow can be characterized by viscosity.

• Viscosity depends on the intermolecular forces present within the fluid.

• Viscosity is highly dependent on temperature.

Key Terms

• viscosity: A quantity expressing a fluid’s resistance to flow. It can be interpreted as a measure of the internal friction in a fluid.

• Laminar Flow: Smooth flow of a fluid in a tube or pipe.

• ​Viscosity is highly dependent on temperature, and therefore, when the value of the quantity is reported, the temperature at which the measurement was made must be included.

• ​Intermolecular Forces Affect the Viscosity of a Substance

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​Capillary Action

Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces.

​Key Points

• The rise or fall of a fluid in a capillary tube is governed by the balance of cohesive and adhesive forces.

• Intermolecular forces are responsible for cohesion and adhesion.

• The narrower the bore of a glass tube, the greater the extent of raising or lowering of the liquid.

Key Terms

• capillary: Pertaining to a narrow tube.

• cohesion: Various intermolecular forces that hold solids and liquids together.

• adhesion: The ability of a substance to stick to an unlike substance.

• meniscus: The curved surface of liquids in tubes, whether concave or convex, caused by the surface tension of the liquid.

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​In thermodynamics, a critical point (or critical state) is the endpoint of a phase equilibrium curve. The most prominent example is the liquid-vapor critical point, the endpoint of the pressure-temperature curve that designates conditions under which a liquid and its vapor can coexist. At higher temperatures, the gas cannot be liquefied by pressure alone. At the critical point, defined by a critical temperature T_c and a critical pressure p_c, phase boundaries vanish.

Multiple Choice

Which of these factors affects Viscosity?

• Temperature

• Colour

• Taste

Multiple Choice

Liquids with very low viscosity flow very _______________________.

• fast

• not at all

• slow

• whenever it wants

Multiple Choice

What is viscosity?

• A liquid's resistance to flow.

• a liquids flow.

• a liquid

• gas to solid.

Multiple Choice

All liquids _____________________.

• have no define shape and can flow

• take the shape of container

• have viscosity

• all of the above

Multiple Choice

As temperature increases viscosity _______________.

• increases

• stays the same

• decreases

Multiple Select

Surface tension is the property of water in which...

• water molecules at the surface tend to stick together.

• water spills easily.

• water tends to be see-through.