Chem. Test #1

Why does water have high surface tension?

Because of the strong hydrogen boning that causes an inward pull that tends to minimize the surface area

Why do particles at the surface of the liquid behave differently than those in the bulk of the liquid?

Because the surface molecules are attracted to the liquid molecules below, but not to the air above

What is a surfactant? How does it work?

A surfactant is a wetting agent such as soap or detergent that interferes with hydrogen bonding between water molecules and reduces surface tension

How can an unusually low vapor pressure of water be explained?

Hydrogen bonds hold water molecules to each other, so the tendency for them to escape the solution is low

How does the structure of ice differ from the structure of water?

Ice is a regular open framework of hydrogen-bonded water molecules arranged like a honeycomb. This structure collapses in liquid water

Explain the role of hydrogen bonds in ice

Hydrogen bonds between water molecules hold the molecules in a regular, open structure

Distinguish between a solution in general, and an aqueous solution

An aqueous solution is a solution that has water as the solvent

Identify the solvent and solute in a solution of table sugar in water

Water=solvent
Sugar=solute

Why is water an excellent solvent for most ionic and polar covalent compounds, but not nonpolar compounds?

Polar water molecules electrostatically attract ions and polar covalent molecules, but nonpolar compounds are unaffected because they have no charge

Suppose an aqueous solution contains both sugar and salt. Can you separate either of these solutes from the water by filtration? explain

No; the molecules and ions are smaller than the pores of the filter

Explain why gasoline does not dissolve in water

Water is polar and gasoline is nonpolar

What particles must be present in a solution if it is to conduct electricity?

ions

Why does molten sodium chloride conduct electricity?

Its ions are free to move toward and electrode

What is meant by a substances water of hydration?

water of hydration is water in the crystal structure of a substance

Explain why a hydroscopic substance can be used as a desiccant

They absorb water vapor from the air

Why is it important to keep some hydroscopic substances in tightly sealed containers?

Because they absorb water from the air

What does efflorescent mean? Under what conditions will a hydrate effloresce?

Efflorescence is the loss of water of hydration that occurs when the hydrate has a higher vapor pressure than that of water vapor in the air

How can you distinguish between a suspension and a solution?

A suspension has large particles that settle to the bottom. The particles in a solution stay suspended

Arrange colloids, suspensions, and solutions in order of increasing particle size.

solutions, colloids, suspensions

What is the Tyndall effect?

the scattering of visible light by colloids and suspensions

Why don't solutions demonstrate the Tyndall effect?

Because the molecules or ions are too small to have reflective surfaces

What causes Brownian motion?

the collisions of molecules of the dispersing medium with the small dispersed colloidal particles

What are two circumstances that help keep colloidal particles in suspension?

Brownian motion and repulsion between like-charhedions absorbed on the surfaces of colloidal particles

How can a colloid be destroyed?

by adding ions with a charge opposite that of the colloidal particles

What is the maximum density of water?

1.00 g/mL

At what temperature does the maximum density of water occur?

4 degrees C

Describe what might happen if you put a sealed, full glass container of water into a freezer

The glass would break because water expands as it freezes

Explain why liquids and gases differ in density and the ability to be compressed

The particles in gas are relatively far apart compared to the particles in a liquid. Because of the extra space between particles, gas is less dense and easier to compress.

Compare the evaporation of a liquid in a closed container with that of a liquid in an open container

In both cases, particles with sufficient kinetic energy move from the liquid to the vapor phase. In a closed container, a dynamic equilibrium is set up between the contained liquid and its vapor

Describe whats happening at the molecular level when a dynamic equilibrium occurs

two opposing processes are occurring at identical rates