Chapter 15 ChemPhys
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Explain why water molecules are polar?
The hydrogen atoms have a slightly positive charge and the oxygen atom has a slightly negative charge
Why do the particles at the surface of the liquid behave differently from those in the bulk of the liquid?
Surface molecules are attracted to the liquid molecules below but not to the air. Molecules inside the liquid are attracted in all directions.
Why does water have a high surface tension?
Strong hydrogen bonding causes an inward pull that tends to minimize the surface area.
Describe some observable effects that are produced by the surface tension of a liquid.
Drops are spherical, objects denser than the liquid can float on its surface
What is a surfactant? Explain how it works.
It is a wetting agent such as soap that interferes with hydrogen bonding between water molecules and reduces surface tension
How can the 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.
Explain why water has a relatively high boiling point.
Water has a relatively low vapor pressure
Explain why bodies of water with large surface areas such as lakes and oceans do not evaporate rapidly
Water has a low vapor pressure
What characteristic of ice distinguishes it from other solid substances?
Ice is less dense than liquid water. The molecules in ice are farther apart in ice than in liquid water.
Explain the role of hydrogen bonds in ice.
Hydrogen bonds between water molecules hold the molecules in a regular, open structure.
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.
What would be some of the consequences if ice were denser than water?
Bodies of water would freeze from bottom to top. This would kill many forms of aquatic life.
Distinguish between a solution in general and an aqueous solution.
An aqueous solution is a solution that has water as the solvent.
In the formation of a solution, how does the solvent differ from the solute?
The solvent is the part of the solution present in the largest amount. It is the dissolving medium. The solute is the dissolved particles.
Describe the process of solvation
Solvent molecules surround positively charged and negatively charged ions.
Why is water an excellent solvent for most ionic and polar covalent compounds but not for non-polar compounds?
Polar water molecules electrostatically attract ions and polar covalent molecules, but non-polar compounds are unaffected because they have no charges
Explain why gasoline doesn't dissolve in water
Water is polar and gasoline is non-polar
What particles must be present in a solution in order to conduct an electric current?
What is the main distinction between an aqueous solution of a strong electrolyte and an aqueous solution of a weak electrolyte?
A strong electrolyte is almost totally ionized
What is meant by a substance's water of hydration?
Water is a crystal structure of a substance
Some hydrates are efflorescent. Explain what that means. Under what conditions will a hydrate effloresce?
Efflorescence is the loss of water of hydration that occurs when the hydrate is a higher vapor pressure than that of the water vapor in air
Explain why a hygroscopic substance can be used as a desiccant?
Hygroscopic substances can absorb water vapor from the air and create a dry environment in a sealed container.
Why is it important to keep some hygroscopic substances in tightly sealed containers?
They absorb water vapor from the air
Colloids, suspensions, and solutions by increasing particle size
solutions, colloids, suspensions
How could you tell through an observation among the three?
Colloids and suspensions exhibit the Tyndall effect but the solution doesn't. The particles in a suspension will settle out over time.
What is the Tyndall effect?
It is the scattering of light by colloids and suspensions.
Why don't solutions demonstrate the Tyndall effect?
The molecules or ions are too small to have reflective surfaces
What causes Brownian motion?
Collisions of molecules of the dispersing medium with the small, dispersed colloidal particles
What are 2 circumstances that help keep colloidal particles in a suspension.
Brownian motion and repulsion between like-charged ions absorbed on the surfaces of colloidal particles
What makes a colloidal dispersion stable?
The addition of an emulsifier
Explain why the dissolved component doesn't settle out of a solution.
Random collisions of the solvent molecules with the solute particles provide enough force to overcome gravity
the amount of a substance that dissolves in a given quality of solvent at specified conditions of temp. and pressure to produce a saturated solution
a solution containing the max amount of solute for a given amount of solvent at a constant temp. and pressure
a solution that contains less solute than the saturated solution at a given temp. and pressure
describes liquids that dissolve in each other
describes liquids that are insoluble in each other.
If a saturated solution of sodium nitrate is cooled, what can be observed?
crystals will form
Can a solution with undissolved solute be supersaturated? Explain
No, if there were undissolved solute, the excess solute would come out of a supersaturated solution
What is the effect of pressure on the solubility of gases in liquids?
Solubility increases with pressure
Why is the molarity of a solution more meaningful than whether a solution is dilute or concentrated?
Dilute and concentrated are relative terms and not quantitative. Molarity provides the exact number of moles of a solute per liter of solution.
The number of moles of solute dissolved in one liter of solution
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