Honors Chemistry II- Ch 13, 15, 16- Textbook Questions

what are colligative properties? identify three and explain why each occurs

-Colligative properties are properties of a solution that depend only on the number of solute particles; boiling point elevation, freezing point depression, and vapor pressure lowering. -Boiling points are elevated because shows of solvent form around solute particles, reducing the amount of solvent molecules that have sufficient energy to escape the solution; relative to the pure solvent, the amount of energy required to cause vaporization or boiling increases -solutes disrupt the ordering of the solvent structure so more Connecticut Energy must be withdrawn from a solution for it to solidify -this lowers the freezing point of a solution

Describe evaporation, vapor pressure, and boiling point

-Evaporation--> is the conversion of a liquid to a gas or vapor when the liquid is below the boiling point -Vapor Pressure--> is the force per unit area exerted by the vaporized particles on the walls of a sealed container -boiling point--> is the temperature at which the vapor pressure of the liquid becomes equal to the external pressure

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

-ICE is regular open framework of hydrogen-bonded water molecules arranged like a honey-comb -this structure collapses in liquid water

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

Liquid A has a vapor pressure of 7.37 kPa at 40 degrees C. Liquid B has a vapor pressure of 18.04 kPa at 40 degrees C. Which liquid would evaporate faster at 40 degrees C? which liquid would boil first?

-Liquid B would evaporate quicker because it has a higher vapor pressure -Liquid A would boil first

Distinguish between the boiling point and the normal boiling point of a liquid

-The boiling point is the temperature at which the vapor pressure equals the external pressure -at normal boiling point, the external pressure is 101.3 kPa

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

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

what causes atmospheric pressure, and why is it much lower on the top of a mountain than it is at sea level?

-atmospheric pressure results from the collisions of particles in air with objects. -there are fewer particles in a given volume of air at the top of a mountain than at sea level

what causes Brownian motion?

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

-some hydrate are efflorescent. Explain what that means. -under what conditions will a hydrate effloresce?

-is the loss of water of hydration that occurs when the hydrate has a higher vapor pressure then that of the air

describe what happens on a particle level when a liquid is at its boiling point

-particles overcome the attractive forces and move faster -pressure is equal -when a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil

why is water an excellent solvent for most ionic and polar covalent compounds but not for non polar compounds?

-polar water molecules electrostatic ally attract ions and polar covalent molecules, but non polar compounds are unaffected, because they have no charges

what is the Tyndall effect?

-scattering visible light by colloids and suspensions

how can you distinguish between a suspension and a solution?

-suspension has large particles that settle to the bottom -particles in a solution stay suspended

why don't solutions demonstrate the Tyndall effect?

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

explain why evaporation leads to cooling of the liquid

-the particles with the highest kinetic energy escape first -the particles left have a lower kinetic energy than those that escaped -As evaporation takes place, the liquids temperature decreases because there is less kinetic energy -therefore, evaporation is a cooling process

what is the typical particle size in a colloidal dispersion?

1 nm to 1000 nm

Why is the equilibrium that exists between a liquid and its vapor in a closed container called a dynamic equilibrium?.

Although the net amounts of vapor and liquid remain constant, some molecules are evaporating while an equal number of particles are condensing

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

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

In a series of liquids, as the intermolecular forces of attraction strengthen, would you expect the vapor pressure to increase or decrease?.

Decrease -as the attractions become stronger, it becomes more difficult for

Describe the effect that increasing temperature has on vapor pressure of liquid

It increases the average kinetic energy, which increases the vapor pressure

Explain why increasing the temperature of a liquid increases it rate of evaporation

More molecules have enough energy to escape attractions within the liquid

Would you expect a dynamic equilibrium in a liquid in an open container?

No -in an open container, most of the participles that escape from the surface of the liquid as vapor do not condense back to liquid

What happens to the average kinetic energy of the water molecules in your body when you have a fever?

The average kinetic energy of the molecules is greater because, by definition,a fever is a state of increased body temperature

Explain why a liquid stays at a constant temperature while it is boiling.

The temperature is constant while the liquid boils because the added energy is used to vaporize the molecules

Describe what is happening at the molecular level when a dynamic equilibrium occurs

Two opposing processes are occurring at identical rates

When you remove the lid from a food container that has been left in a freezer for several months, you discover a large collection of ice crystals on the underside of the lid. Explain what happened,

Water from the food sublimes and condensed on the lid

what is a surfactant? explain how it works.

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

explain which properties of water are responsible for these occurrences... a) water in tiny cracks in rocks helps break up the rocks when it freezes b) water beads up on a newly waxed car c) a longer time is needed for a teaspoon of water to evaporate than a teaspoon of alcohol

a) water expands when it freezes b) water is polar and wax is non polar, and water has a high surface tension c) water has a lower vapor pressure than alcohol

how can a colloid be destroyed?

add ions with a charge opposite that of the colloidal particles

distinguish between a solution in general and an aqueous solution

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

what is the typical particle size in a suspension?

greater than 1000 nm

arrange these liquids in order of increasing surface tensions: water (H2O), hexane (C6H14), ethanol (C2H5OH)

hexane, ethanol, water

explain the role of hydrogen bonds in ice

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

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

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 an electrode

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

no the molecules and ions are smaller than the pores of the filter

arrange colloids, suspensions, and solutions in order of increasing particle size

solutions, colloids, suspensions

why does water have a high surface tension?

strong hydrogen bonds causes an inward pull that tends to minimize the surface area

why do the particles at the surface of a 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 above

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

the container would break because water expands as it freezes

in old-fashioned ice cream makers, a mixture of rock salt and ice is used to cool the creamy mixture as it is stirred. What is the purpose of the salt?

the salt lowers the freezing point of the ice-water cooling mixture

explain why a hygroscopic substance can be used as a desiccant

they absorb water vapor from the air

why is it important to keep some hygroscopic substances in tightly sealed containers?

they absorb water vapor from the air

what is meant by a substance's water of hydration?

water in crystal structure of a substance

explain why gasoline does not dissolve in water

water is polar, gasoline is nonpolar

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

water: solvent sugar: solute

explain how a decrease in the vapor pressure of a solution results in an increase in its boiling point

when vapor pressure is lowered relative to pure solvent, more energy must be supplied to reach the boiling point; the boiling point is increased relative to pure solvent