Chemistry Unit 7 Review

The separation of charges within a polar molecule is called a(n)

dipole.

Why might softened water not be good for some one who is trying to reduce their dietary sodium ion intake?

Water softeners work by replacing the calcium and magnesium ions of the water with sodium ions; softened water contains increased levels of sodium ions.

How many moles of sugar, C12H22O11, are there in 200. grams?

0.585 moles (Do the Pickett Fence Method)

If you need 10 moles of sucrose, how many liters of a 4.0 molar solution would you need?

2.5 L

A sealed plastic bottle is filled with enough sand so that the bottle floats just beneath the surface in ocean water. Some sand is then removed and the bottle is then placed in some fresh water where it floats just beneath the surface. What is true about the amount of sand that was removed from the bottle?

The amount of sand removed from the plastic bottle equals the amount of salt dissolved in the ocean water.

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.

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

Fluorine is a relatively

small atom.

A 1 molar solution of sugar water contains

Not enough information is given.

Does a plastic bottle of fresh water sink or float in the ocean? Why?

Floats; The bottle filled with fresh water floats in ocean water because it is less dense than the ocean water.

The charges with sodium chloride are all balanced for every positive sodium ion there is a corresponding negative chloride ion. Since its charges are balanced, how can sodium chloride be attracted to water, and vice versa?

As a water molecule gets close to the sodium chloride it can distinguish the various ions and it is thus attracted to an individual ion by ion-dipole forces.

How many moles in 12 grams of carbon? Then, which statement best describes a mole?

It is a very large number chemists use to count atoms or molecules.

What is desalinization? Then, which of the following statements about desalinization is untrue?

You can use osmosis to remove salt from saltwater.

What is the molarity when water is added to 2 moles of sodium chloride to make 0.5 liter of solution?

4 M

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.

What is a mole? Then, which has the most atoms?

All singular atoms have the same number of atoms.

The warming of a saturated solution of calcium carbonate, CaCO3, produces

a precipitate.

Why are ion-dipole attractions stronger than dipole-dipole attractions?

The magnitude of the electric charge associated with an ion is much greater.

What is a hydrogen bond?

a special type of dipole-dipole attraction involving hydrogen bound to a highly electronegative atom

Does a low melting point indicate strong or weak attractions among molecules? Then, which of the following would have the lowest melting point?

A low melting point indicates weak attractions among molecules;
CF4 (it’s nonpolar)

If you need 3.01 x 10(23) molecules of sucrose, how many liters of a 4.0 molar solution would you need?

0.125 L

What property primarily determines the effect of temperature on the solubility of gas molecules?

the kinetic energy of the gas

What is a saturated solutions? Then, which of the following statements describes a saturated solution?

All of these: a solution where the solvent cannot dissolve any more solute

a solution of salt water with salt at the bottom

a carbonated beverage with bubbles

What is osmosis? Then, which of the following describes reverse osmosis?

a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane; High pressure saltwater is forced against a semipermeable membrane and fresh water comes out.

Cells at the top of a tree have a higher concentration of sugars than cells at the bottom. How might this fact assist a tree in moving water upward from its roots?

Water is pushed upwards by osmostic pressure.

What is an induced dipole-induced dipole attraction? Then, which of the following would have the smallest number of induced dipole-induced dipole interactions?

An induced dipole is a temporary separation of positive and negative charge in a neutral, nonpolar atom or molecule, caused by the electric field of a nearby ion or polar molecule, creating a weak, short-lived attraction; C6H14 (the atom/molecule with the least electrons)

Why might a solvent like turpentine be better for removing grease and grime than water?

All of these; Like dissolves like.

Oil and grease have similar interatomic forces as the turpentine and so are more soluble.

Water is too polar and doesn't interact well with the nonpolar oils.

Oil and grease have very limited solubility in the water.

What is reverse osmosis? Then, which of the following accurately describes regular osmosis?

a process by which a solvent passes through a porous membrane in the direction opposite to that for natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure; The more concentrated solution absorbs water from the less concentrated solution.

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

When is a solution saturated? Then, which of the following solutions is the most concentrated?

when it contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature; 0.5 liter of water with 50 grams of sugar

What is the "molar"? Then, which of the following best describes a two-molar sucrose solution?

a unit of concentration, specifically molarity, defined as the number of moles of solute dissolved in one liter of total solution; one liter of solution that contains 2 moles of sucrose

Deuterium oxide, D2O, and water, H2O, have the same chemical structure and differ only in that D2O possesses the deuterium isotope of hydrogen, whereas water possesses the protium isotope. Deuterium oxide, also known as heavy water, is 11 percent heavier than water. Might you expect its boiling temperature also to be about 11 percent greater? Why or why not?

Since they have the same chemical structures, there is a similar molecular attraction between the molecules, so their boiling temperatures are similar.

What is a hydrogen bond? Then, which of the following molecules is most likely to show a hydrogen bonding interaction?

a strong electrostatic attraction between a slightly positive hydrogen atom (covalently bonded to N, O, or F) and a slightly negative atom (like N, O, or F) in another nearby molecule or part of the same molecule; CH3OH

A single Velcro hook is weak. But a two strips of Velcro are difficult to pull apart. Why? Then, which of the following would have the highest boiling point?

C12H26

What is the purpose of adding aluminum salts and a base to water during water treatment?

The two together gel and trap dirt and bacteria.

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.

Why do sticky molecules have higher boiling points? Then, which of the following would have the highest boiling point?

I2

Why are induced induced dipoles relatively weak? Then, which of the following is most likely to have the weakest induced dipole-induced dipole interaction?

because they are transient, temporary, and depend on constantly fluctuating electron distributions rather than permanent charge separation; F2 (least electrons)

How does the hydrogen bond help with solubility in water? Then, which of the following might have the lowest solubility in water?

enabling polar solutes to form strong, favorable intermolecular attractions with water molecules (hydration), allowing them to dissolve readily; CH3CH3 (largest non-polar)

Why is methane nonpolar? Then, which of the following molecules is most likely to show a dipole-dipole attraction?

symmetry cancels out the polar bonds; CH3OH

How many molecules of sucrose are in 0.5 L of a 2 molar solution of sucrose?

6.02 x 10(23) molecules of sucrose

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.

What is potable water? Then, which of the following is not a typical use for potable water?

water that is safe for humans to drink; irrigation

Why is a large quantity of water used in industrial processes in the U.S. purified by desalinization?

The sources are brackish or metal ion rich.

How can you tell whether a sugar solution is saturated or not?

Cool the solution to see if there is a precipitate.

If nitrogen, N2, were pumped into your lungs at high pressure, what would happen to its solubility in your blood stream?

The greater the pressure, the greater the solubility.

Why do red blood cells, which contain an aqueous solution of dissolved ions and minerals, burst when placed in fresh water?

The fresh water acts to dissolve the blood cell wall. (supposedly, but its actually wrong) The fresh water acts to dissolve the blood cell wall. (This is the real correct answer)

Why are noble gases infinitely soluble in noble gases?

Noble gases can be mixed homogeneously in any proportion.

A saturated solution of compound X in water has a greater concentration than does a saturated solution of compound Y. Does it follow that compound X is also more soluble in water?

Yes, compound X is more soluble than is compound Y because a greater concentration in water can be obtained.

How many molecules of sucrose are in a 0.5 moles of sucrose?

3.1 x 10(23) molecules of sucrose

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 fluids_much 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.

What makes for good solubility in water? Then, which of the following might have the best solubility in water?

Good solubility in water is primarily driven by the "like dissolves like" principle, where polar and ionic substances dissolve best in polar water as well as hydrogen bonds; CH3OH

Might reverse osmosis be used to obtain fresh water from a sugarwater solution?

Yes, reverse osmosis can be applied to any aqueous solution for the generation of fresh water.

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 a dipole? Then, which of the following is the weakest form of interatomic attraction?

a separation of opposite electrical charges (positive and negative) or magnetic poles;
an induced dipole-induced dipole interaction