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138 Cards in this Set

  • Front
  • Back

What are cohesive forces?

Attractions between molecules that hold them together.

Which geometrical shape has the lowest surface-area-to-volume ratio, allowing the maximum number of molecules to be completely surrounded by other molecules?

The sphere

What is a solution?

Homogeneous mixtures of liquids with solids or other liquids.

T/F Molecules within gases are separated by small distances and move at low velocities.

False, Molecules within gases are separated by large distances and move at high velocities.

T/F Molecules in liquids are in intimate contact and interact strongly; however, they are still free to move around and past each other.

True

Molecules in solids are locked in place and only vibrate about a fixed point.

True

T/F In liquids, the attractions are strong enough to hold the molecule in one place.

False, the attractions are not strong enough to hold the molecule in one place, therefore they continually move around.

If a molecule in liquid form happened to be moving particularly fast when it reached the surface, it could overcome the relatively fewer attractions at the surface and shoot off into the air. What is this called?

Evaporation

The mobility of individual molecules gives liquids its properties. What are properties of liquids? (7)

Assumes container's shape


Flows and can be poured


Can evaporate


Can be boiled


-Incompressible


-Variable shape


-Fixed volume

The close contact between molecules in liquids is responsible for other properties such as their ________________ and ______ _________ compared with gases.

Incompressibility


High Density

T/F The water molecules that compose ice are identical in every way to those composing liquid water, just their movement and arrangement are different.

True

T/F In ice, the thermal energy is lower; molecules move less, allowing them to interact more.

True

What are crystalline solids?

Solids in which the constituent particles have long-range order. Ex. Ice.

The repeating pattern of the molecules or atoms of a crystalline solid is called what?

Crystalline structure

Whether a substance is a solid, a liquid, or a gas depends on a competition between two factors. What are the two factors?

The strength of cohesive forces between its molecules or atoms.


Thermal energy

What is thermal energy?

Random molecular motion.


The higher the temperature is, the greater the motion.

What is the definition of melting point?

The temperature at which a solid melts.

What does melting point depend on?

On the strength of the cohesive forces of the atoms or molecules that compose it.


The stronger the force is, the higher the melting point.

What is the definition of boiling point?

The temperature at which a liquid boils.

T/F Both liquid H2O and gas H2O are still water. No chemical bonds within the molecule have been broken, only the forces among the molecules have been overcome.

True

The strength of the cohesive forces among molecules is related to what?


And can be estimated by what?

The molecule's structure.


By examining the structure.

Substance A is composed of molecules that have stronger intermolecular forces than the molecules that compose substance B. Which substance has a lower boiling point?

Substance B. Weaker intermolecular forces result in lower melting and boiling points.

B

If not for _________ forces, all matter would be gaseous.

Cohesive forces

There are three major cohesive forces that occur between molecules. What are they?

Dispersion force


Dipole force


Hydrogen bond

List the three major cohesive forces in order of strength from weakest to strongest.

Dispersion force


Dipole force


Hydrogen bond

Which is the weakest cohesive force?

Dispersion force

Dispersion forces result in what, which in turn form what?

They result in small fluctuations in the electron clouds of atoms and molecules, which result in instances where electrons are not evenly distributed in the molecule or atom, forming an instantaneous dipole.

What is an instantaneous dipole?

It is like a polar bond but the difference is that polar bonds are permanent dipoles, whereas instantaneous dipoles are temporary.

T/F Instantaneous dipoles cause attractions between molecules.

True

An instantaneous dipole on one molecule or atom induces what on neighboring molecules or atoms?

Induces other instantaneous dipoles

The magnitude of the dispersion force is proportional to what of the molecule or atom?

The molar mass

The heavier a molecule or atom is, the stronger the what?

The dispersion force

What is A an example of?
What is B an example of?

What is A an example of?


What is B an example of?

A is an example of an instantaneous dipole.


B is an example of an instantaneous dipole inducing instantaneous dipoles in other molecules and rearranging so that negatives line up with positives.

As the molar mass __________ , the strength of the cohesive forces __________ and the boiling point __________ .

Increases


Increases


Increases

T/F Molar mass alone determines boiling point.

False, Molar mass alone does not determine boiling point.

T/F Molar mass can only be used as a guide to the magnitude of dispersion forces when comparing a family of similar elements or compounds; it is not useful in comparing widely different elements or compounds.

True

T/F Dipole forces, stronger than dispersion forces, are present in polar molecules.

True

Polar molecules have ___________ dipoles that result in strong attractions between ___________ molecules.

Permanent dipoles


Neighboring molecules

What are polar bonds?

Bonds in which electrons are unevenly shared between the bonding atoms.

Which has the higher boiling point, Cl2 or Br2?

Br2 because it has the higher molar mass.

Which has the higher boiling point, C8H18 or C10H22?

C10H22

T/F Hydrocarbons - compounds that contain ONLY carbon and hydrogen - are nonpolar.

True

Is Methane (CH4) polar or nonpolar?

Nonpolar

Is Hexane (C6H14) polar or nonpolar?

Nonpolar

Is Benzene (C6H6) polar or nonpolar?

Nonpolar

T/F Because polar molecules have permanent dipoles, the cohesive attractions between neighbors are stronger than in nonpolar molecules. Consequently, a polar molecule has a higher boiling point than a nonpolar molecule of similar molecular weight.

True

Which has stronger cohesive forces and therefore a higher boiling point, Ethane (CH3CH3) or Formaldehyde (CH2O)?

Formaldehyde. It is a polar molecule meaning it has stronger, dipole cohesive forces, giving it a higher boiling point.

T/F Polar molecules are attracted to each other, and they are strongly attracted to nonpolar molecules.

False, Polar molecules ARE attracted to each other, but they are NOT strongly attracted to nonpolar molecules.


Oil and water not mixing together is an example of what?

Polar molecules not being attracted to nonpolar molecules.

Determine whether the following molecules are polar or nonpolar.




a. O2


b. H-Cl


c. CHCl3


d. CH3CH3


e. CH3OH


f. CCl4

a. Nonpolar


b. polar


c. polar


d. nonpolar


e. polar


f. nonpolar

Determine whether the following molecules are polar or nonpolar.



a. HF


b. N2


c. CH3Cl


d. CH3CH2OH


e. CH3CH2CH2CH2CH3

a. Polar


b. Nonpolar


c. Polar


d. Polar


e. Nonpolar

What is a hydrogen bond?

The cohesive force that polar molecules have when containing H atoms bonded to either F, O, or N atoms.

T/F A hydrogen bond is a cohesive attraction between MOLECULES and should not be confused with a CHEMICAL BOND that holds atoms together to form molecules.

True

T/F One end of soap is polar and the other end is nonpolar.

True

Hydrogen bonds only occur when what is bonded to one of what three possibilities?

Hydrogen to either Nitrogen, Oxygen or Fluorine.

This is an example of what? 

This is an example of what?

Hydrogen bonds (the dashed lines)

This is an example of what? 

This is an example of what?

Hydrogen bonds (the dashed lines)

One of the following molecules is a liquid at room temperature. Which one and why?



CH4


CH3OH


C2H6

CH3OH


This is the only molecule that displays hydrogen bonding.

Which of the following molecules do you expect to have the highest boiling point?




NH3


Ne


O2


NO

NH3


This is the only molecule that displays hydrogen bonding.

Liquids that vaporize easily have a what and are termed what?

High vapor pressure


Volatile

Liquids that do not vaporize easily have a what and are termed what?

Low vapor pressure


Nonvolatile

Why is evaporation slower in water than it is in perfume?

Because water molecules form hydrogen bonds, which are a stronger cohesive force than the ones found in perfume.

Acetone doesn't hydrogen bond. Why not?


C3H6O

Because the hydrogen atoms in acetone are not bonded directly to the oxygen atom in acetone.

What does Endothermic mean?

Accompanied by or requiring the absorption of heat.

What does Exothermic mean?

Accompanied by the release of heat.

A mixture initially contains equal masses of pentane (C5H12), octane (C8H18), and decade. The mixture is left in an open beaker overnight. Do you expect the mixture to contain equal masses of all three components in the morning?

No, all three are hydrocarbons and therefore only have dispersion forces but each molecule has a different molar mass meaning that each molecule's dispersion forces will be of different strengths. So the one with the weakest dispersion force will lose more of its molecules than the others.

What is a solution defined as?


What are some examples of solutions?

A homogeneous mixture of two or more substances.


Gasoline, seawater, coffee, blood plasma...



In a solution, what is the solvent?

The majority component of the solution.

In a solution, what is the solute?

The minority component of the solution.

What is the solvent and the solute in a sugar/water solution?

Solvent - Water


Solute - Sugar

T/F Not all substances form solutions when mixed. For example, oil and water remain separate even when mixed vigorously. Whether or not a solution forms depends on the interactions between the components of the mixture. If the components attract each other, a solution forms. Sugar and water form a solution because sugar molecules and water molecules are both polar and therefore attract one another.

True

What is concentration in regards to solutions?

Concentration is the amount of solute relative to the amount of solvent.

What are five ways expressed in the book to express concentration?

Percent by mass


Percent by volume


Molarity (M)


Parts per Million (ppm)


Milligrams per Liter (mg/L)

What is an example of percent by mass?

5% sugar solution contains 5 g sugar for every 100 g of solution.

What is an example of percent by volume?

3% acetic acid solution contains 3 mL acetic acid for every 100 mL of solution.

Molarity is represented by what?

M

What is molarity?

The number of moles of solute divided by the number of liters of solution.

20 g of NaCl is mixed with enough water to make 500 mL of solution. What is the molarity of the resulting sodium chloride solution?


(NaCl = 58.4 g)



Molar mass is expressed in what units?

g / mol

Draw the equation for molarity.

molarity (M) = moles solute / liters solution

40 g sugar (molar mass = 342 g/mol) is mixed with enough water to make 200 mL of solution. What is the molarity of the resulting sugar solution?



What are the units for molarity?

mol / L

How many grams of NaCl are present in 2.8 L of a 0.53 M NaCl solution? (NaCl = 58.5 g/mol)



How many grams of NaF are present in 1.3 L of a 0.78 M solution? (NaF = 41.99 g/mol)



For solutions, ppm is usually expressed in terms of what and in what unit?

Mass


Grams

Draw the formula for finding the concentration of a solution in ppm.



1 Liter of water weighs approximately how many grams?

1000 g

Draw the formula for finding the concentration of a solution in milligrams per liter.



What is CaCO3?

Calcium Carbonate

What is Calcium Carbonate's chemical symbol?

CaCO3

A 100.0 g sample of hard water is found to contain 0.012 g of calcium carbonate. What is the concentration of calcium carbonate in parts per million?



A 75.0 g sample of tap water is found to contain 8.1 * 10^-5 g of sodium fluoride. What is the concentration of sodium fluoride in parts per million?



A 250 mL sample of tap water is found to contain 0.38 mg of lead. What is the concentration of lead in milligrams per liter?



A 400.0 mL sample of tap water is found to contain 0.22 mg of copper. What is the concentration of copper in milligrams per liter?



Water is highly _______ and contains two O-H bonds that _________ - _______ to other water molecules.

Polar


Hydrogen-Bond

What must happen for water to become a gas?

The hydrogen bonds must be broken. This requires a lot of thermal energy, making the boiling point of water high.

Draw hydrogen bonds in liquid water (molecular structures).



T/F Water contracts when it freezes. Virtually every other liquid expands on freezing.

False, Water expands when it freezes. Virtually every other liquid contracts on freezing.

T/F Ice occupies a greater volume than the water from which it was formed. The lower density of ice relative to liquid water makes ice float rather than sink.

True

What is the name of the process in the frozen food industry where food is frozen very quickly to prevent water molecules from ordering in their ideal crystalline structure and results in less expansion and therefore less cell rupture?

Flash Freezing

What percentage of water on Earth is in readily usable forms?


What percentage of Earth's water is in the oceans?

0.0014%


97.4%

What is the Hydrologic cycle?

The cycle that explains how usable land water comes from unusable ocean water.

T/F Water-borne diseases cause about 95% of the world's sickness.

False, Water-borne diseases cause about 80% of the world's sickness.

T/F Virtually no water is pure. Water is a solution containing a number of different elements and compounds.

True

What are the most common impurities in tap water?


Water rich in these things is called what?

Calcium and Magnesium ions


Hard water

How is hard water characterized?

By the amount of calcium carbonate that would form if all the calcium ions in the water reacted to form calcium carbonate.

List the classifications of the hardness of water.

Very Soft: less than 15 ppm CaCO3


Soft: 15-50 ppm CaCO3


Medium: 50-100 ppm CaCO3


Hard: 100-200 ppm CaCO3


Very Hard: more than 200 ppm CaCO3

Does hard water produce adverse health effects?

No

A sample of hard water contains 55.0 ppm CaCO3. If a person consumes 1.50 liters of this water, how many grams of CaCO3 have they consumed? (1.00 g/mL - density of water)



A sample of water contains 2.0 ppm NaF. How many grams of NaF are contained in 25 L of water? (1.00 g/mL - density of water)



There are two categories of water contaminants. What are they?



Biological contaminants


Chemical contaminants

There are three types of chemical contaminants. What are they?

Organic contaminants


Inorganic contaminants


Radioactive contaminants

T/F Boiling water vigorously for several minutes kills most microorganisms.

True

Organic chemical contaminants can be broken down into two types. What are they?

Volatile organics


nonvolatile organics

Biological contamination comes from what?

The dumping of human and animal waste into the ground or rivers and lakes.

Both types of organic contaminants come from what?

Fertilizers


Gasoline


Pesticides


Paints


Solvents

Inorganic contaminants include what?

Asbestos


Nitrates


Mercury


Lead

T/F Because Nitrates are nonvolatile, they are not removed from water by boiling. Boiling results in water with a higher nitrate concentration.

True

How do Nitrates get into water?

Animal waste


Fertilizer


Septic tanks


Sewage

T/F Nitrates pose little danger to humans.

False, Nitrates pose an immediate danger to humans.

Radioactive contaminants include what?

Uranium


Radium


Radon

An older home has lead pipes. Should you boil the water that comes out of the pipes before drinking it? Why or why not?

No. Lead is not volatile; therefore, boiling water that is contaminated with lead will only make the water more concentrated in lead. Some of the water boils away, but virtually all of the lead is left behind.

How many milligrams of chlorobenzene are present in 45 L of water with a chlorobenzene concentration of 0.12 mg/L?



How many milligrams of nitrate are present in 185 L of water with a nitrate concentration of 15 mg/L?



What does SDWA stand for?

Safe Drinking Water Act

When and why was the SDWA enacted?


When and how was the SDWA amended?

1974


To ensure high water quality for all Americans.


1986


It was amended to allow the EPA to establish maximum contaminant levels for 90 different contaminants likely to be found in public drinking water systems.

What does MCLs stand for?

Maximum contaminant levels

What must the water supplier do if any of the contaminants controlled by the EPA are above the maximum contaminant level?

- Remove the contaminant as quickly as possible


- Must notify the state agency of the violation


- Must notify the consumer

This is a picture of the steps taken for public water treatment. Fill in the blanks.

This is a picture of the steps taken for public water treatment. Fill in the blanks.



If you receive your drinking water from a public water provider, the EPA believes what?

That home treatment is unnecessary of the protection of your health but that home treatment might be good for water hardness, poor clarity, and undesirable taste.

T/F Unless you get a notice from your water provider stating otherwise, the water from your tap is safe to drink over a lifetime.

True

There are three types of home water treatment talked of in the book. What are they?

Carbon Filtration


Water softening


Reverse osmosis

Which is the most inexpensive home water treatment?

Carbon filtration

Which is the most common water treatment?

Water softening

What is a Zeolite and with which home water treatment is it associated?

Water softening


Zeolites are solid materials with a rigid, cagelike structure that can hold metal ions. Hard water is passed through them, which exchanges the metal ions, usually sodium, for the hard water producing calcium and magnesium ions.

What is osmosis?

A naturally occurring process in which water flows from an area of low solute concentration to high solute concentration.

What happens when treating water using reverse osmosis?

Pressure is applied to the salt water side of the membrane, forcing water through the membrane in reverse. As the salt water solution flows through the membrane, water passes through, but the salt does not.