Chem 1010 - Quiz 7
Which of the following would have the smallest number of induced dipole-induced dipole interactions?
*******NOT -C12H26 (nonpolar molecule) OR -C8H18 (nonpolar molecule)
What happens when the molecule-to-molecule attractions in the solute are comparable to those in the solvent?
*******NOT -The material has only limited solubility in the solvent. OR -The solute does not dissolve in the solvent.
Chlorine, Cl2, is a gas at room temperature, but bromine, Br2, is a liquid. Explain.
*******NOT -The smaller chlorine molecules are able to pack together in a tighter physical orientation. OR -Chlorine atoms are larger and this makes the formation of induced dipole-induced dipole attractions more favorable.
How is the solubility of a solid affected by temperature?
-As temperature goes up, the solubility goes up. -As temperature goes down, the solubility goes down.
Why is it important to conserve fresh water?
-It is expensive to purify nonpotable water. -As the human population grows, so does our need for fresh water. -There is little fresh water available to us on our planet.
Why might a solvent like turpentine be better for removing grease and grime than water?
-Like dissolves like. -Water is too polar and doesn't interact well with the nonpolar oils. -Oil and grease have very limited solubility in the water. -Oil and grease have similar interatomic forces as the turpentine and so are more soluble.
Why does oxygen have such a low solubility in water?
-Water and oxygen only attract one another by means of weak dipole-induced dipole attractions. -Water's attraction for itself is stronger than its attraction for oxygen molecules.
Which of the following substances is pure?
-an element -a covalent compound consisting of one type of molecule -an ionic compound consisting of sodium and chlorine ions
Which of the following material phases cannot form a solution?
-liquids -solids -gases
What is the purpose of allowing water to cascade or bubble in a fountain during the purification process?
-to remove radioactive gases -to remove unpleasant smelling chemicals like sulfur -to mix air into the water and improve flavor
How is the solubility of a gas affected by temperature?
As temperature goes down, the solubility goes up.
Which of the above might best describe how soap behaves in a nonpolar solvent like turpentine?
C
Which of the following might best describe the product obtained from soap and hard water (i.e., soap scum)?
C
Which of the following would have the lowest melting point?
CF4 (nonpolar molecule)
Which of the following might have the best solubility in water?
CH3OH (polar molecule)
Which of the following molecules is most likely to show a hydrogen bonding interaction?≡
CH3OH (polar molecule)
Which of the above would best describe how soap behaves in water?
D
Which of the following is most likely to have the weakest induced dipole-induced dipole interaction?
F2 (nonpolar molecule)
Which of the following molecules would you expect to be the most strongly attracted to a Cl- ion?
H-F (polar molecule)
Which of the following describes reverse osmosis?
High pressure saltwater is forced against a semipermeable membrane and fresh water comes out.
At 10oC, which is more concentrated ---- a saturated solution of sodium nitrate, NaNO3, or a saturated solution of sodium chloride, NaCl? (See figure shown below) .
NaNO3
Based on atomic size, which would you expect to be more soluble in water: helium, He, or nitrogen, N ?
Nitrogen atoms are bigger and so nitrogen molecules should be more soluble in water due to greater dipole-induced dipole attractions.
In which of the following molecules will water induce a temporary dipole?
O2 (nonpolar molecule) CO2 (nonpolar molecule) N2 (nonpolar molecule)
Phosphate ions, PO43-, were once added to detergents to assist in cleaning. What function did they serve?
Phosphate ions would bind to and remove calcium ions, thus acting as a water softening agent.
Which of the following molecules is most likely to show a dipole-dipole interaction?
SO2 (polar molecule)
How necessary is soap for removing salt from your hands?
Soap is not at all necessary for removing salt from your hands. The strong ion-dipole interactions between fresh water and the salt are most sufficient to lift the salt away from your hands.
What is the main difference between a soap and a detergent?
Soaps are made from fatty acids, detergents are have a variety of nonpolar tail structures.
How are intermolecular forces and solubility related?
Solubility depends on the solvent's ability to overcome the intermolecular forces in a solid.
Describe what usually happens to a hot solution that is saturated with a solid as it cools.
Some of the solid comes out of the solution.
Two chemical structures are shown, one of a typical gasoline molecule and the other of a typical motor oil molecule. Which is which? Base your reasoning not on memorization but rather upon what you know about molecular interactions and the various physical properties of gasoline and motor oil. Note that motor oil is more viscous or sticky than gasoline.
Structure A represents motor oil, illustrating a molecule with greater induced dipole-induced dipole molecular interactions thus, the molecules are strongly attracted to one another.
Fish don't live very long in water that has just been boiled and brought back to room temperature. Suggest why.
The boiling process removes the air that was dissolved in the water. Upon cooling the water is void of its usual air content, hence, the fish drown.
Why do water heaters lose their efficiency quicker in households with hard water?
The calcium carbonate on the inner surface of the hot water tank builds up to the point that it insulates the water from the heating element.
If you were to increase the pressure of a gas above a liquid (such as by pressing a piston above a liquid) what happens?
The gas is forced into solution and the solubility increases.
Why is the surface area of a gecko's foot so extensive?
The greater the surface area the greater the number of induced dipole-induced dipole forces of attraction that can occur between the gecko's foot and the surface.
Why might sodium carbonate (washing soda, Na2CO3) be added to hard water to aid in cleaning?
The hard ions in the water are more attracted to the carbonate ions -2 charge.
The air that a scuba diver breathes is pressurized to counteract the pressure exerted by the surrounding water. Under these conditions, excessive amounts of nitrogen dissolves in bodily fluids, such as blood. If the diver ascends to the surface too rapidly, the excessive nitrogen bubbles out of the bodily fluidsÑmuch like carbon dioxide bubbles out of a soda immediately after its has been opened. This results in a painful and potentially lethal medical condition known as the bends. Why does breathing a mixture of helium and oxygen rather than air help divers to avoid getting the bends?
The helium is less soluble in the bodily fluids and so less dissolves for a given pressure. Upon decompression, there is less helium to "bubble out" and cause potential harm.
From the schematic below: why do nonpolar molecules have a difficult time passing through the bilipid layer?
The nonpolar molecules have a difficult time getting past the ionic heads of the fatty acid molecules, which are surrounded by water molecules.
What is the special property of a semipermeable membrane that makes osmosis possible?
The pores in the membrane only allow water to pass through.
What makes a semipermeable membrane selective for one chemical species but not another?
The pores in the membrane select by size, they are big enough for water only.
What is the purpose of adding aluminum salts and a base (slaked lime, Ca(OH)2)to water during water treatment?
The two together gel and trap dirt and bacteria.
What is happening at the molecular level when a polar molecule like water interacts with a typical sodium ion? Hint: See figure 7.1 on page 196 of your text.
The water molecule aligns such that the oxygen interacts with the sodium.
Would you expect to find more dissolved oxygen in polar or tropical ocean waters? Why?
There would be more dissolved oxygen in the polar oceans because the solubility of oxygen in water decreases with increasing temperature.
When you set a pot of tap water on the stove to boil, you'll often see bubbles start to form well before boiling temperature is ever reached. Explain this observation.
These initial bubbles are the gases that were dissolved in the water coming out of solution. The solubility of gases in water decreases with increasing temperature.
Why isn't distillation used commercially to purify water?
Water requires large amounts of energy to boil affordably.
Which of the following is the strongest form of interatomic attraction?
a chemical bond
Which of the following describes an aqueous solution?
a mixture of pure substances dissolved in water
What is a hydrogen bond?
a special type of dipole-dipole attraction involving hydrogen bound to a highly electronegative atom
Which of the following is the weakest form of interatomic attraction?
an induced dipole-induced dipole interaction
Plastic wrap is made of nonpolar molecules and is able to stick well to polar surfaces, such as glass, by way of dipole/induced dipole molecular attractions. How is it that plastic wrap also sticks to itself so well?
by way of induced dipole-induced dipole molecular attractions
Which of the following intermolecular forces best describes why molecules like sucrose also known as table sugar (which has many OH groups) are very water soluble?
hydrogen bonding
A sample of steel is composed of 5 percent carbon and 95 percent iron. Which is the solvent?
iron
Which of the following is not a typical use for potable water?
irrigation
What is the difference between a dipole-dipole interaction and an ion-dipole interaction?
one involves dipole attraction between neutral molecules while the other involves dipole interactions with ions
A dipole is a ________.
separation of charges
A gemstone is an example of a ________.
solid solution
In a solution made from one teaspoon of sugar and one liter of water, which is the solute?
sugar
What property primarily determines the effect of temperature on the solubility of gas molecules?
the kinetic energy of the gas
During osmosis ________.
the water moves into the concentrated solution faster than it leaves
What is the purpose of treating water with chlorine gas or ozone during water purification?
to kill bacteria