Chapter 16
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. -*Both A and B
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. -* Both A and B
Why might a solvent like turpentine be better for removing grease and grime than water?
-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. -Like dissolves like. -*all of the above
Why does oxygen have such a low solubility in water?
-Water's attraction for itself is stronger than its attraction for oxygen molecules. -Water and oxygen only attract one another by means of weak dipole-induced dipole attractions. -* Both A and B are true.
Which of the following statements describes a saturated solution?
-a carbonated beverage with bubbles -a solution of salt water with salt at the bottom -a solution where the solvent cannot dissolve any more solute -*all of the above
Which of the following material phases cannot form a solution?
-solids -gases -liquids -*All of the above can form solutions.
If you need 3.01 × 1023 molecules of sucrose, how many liters of a 4.00 molar solution would you need?
0.125 L
Which of the following solutions is the most concentrated?
0.5 liter of water with 50 grams of sugar
How many moles of sugar, C12H22O11, are there in 200. grams?
0.585 moles
A sample of water that is 99.9999 percent pure contains 0.0001 percent impurities. Consider from Chapter 1 that a glass of water contains on the order of a trillion trillion (1 × 1024) molecules. If 0.0001 percent of these molecules were the molecules of some impurity, about how many impurity molecules would this be?
1,000,000,000,000,000,000 (one million trillion: 1 × 1018)
What is the molarity of 0.5 liters of a solution with five moles of sucrose in it?
10 molar
If you need 10 moles of sucrose, how many liters of a 4.0 molar solution would you need?
2.5 L
How many grams of sugar (sucrose) are there in 5 liters of sugar water that has a concentration of 0.5 grams per liter of solution?
2.5g
A solid has a solubility at room temperature of 78 grams per liter. If 1.0 L of a hot solution containing 100. g of solute is cooled to room temperature, how much solid is formed?
22 g
How many molecules of sucrose are in a 0.5 moles of sucrose?
3.01 × 1023 molecules of sucrose
What is the sum of the atomic masses of all the atoms in sucrose, ?
342 amu
If the solubility of a compound is 72 grams per liter, how many grams of the compound will dissolve in 0.50 liters?
36 g
What is the molarity when water is added to 2 moles of sodium chloride to make 0.5 liter of solution?
4 M
How many grams of sodium chloride are needed to make 15 L of a solution that has a concentration of 3.0 g per liter of solution?
45 g
How many moles of water are there in 100. grams of water?
5.55 moles
How many molecules of sucrose are in 0.5 L of a 2 molar solution of sucrose?
6.02 × 1023 molecules of sucrose
A student is told to use 20.0 grams of sodium chloride to make an aqueous solution that has a concentration of 10.0 grams of sodium chloride per liter of solution. Assuming that 20.0 grams of sodium chloride has a volume of 7.5 milliliters, about how much water will she use in making this solution?
9.9925 L
Mixtures can be separated into their components by taking advantage of differences in the chemical properties of the components. Why might this separation method be less convenient than taking advantage of differences in the physical properties of the components?
A chemical property involves a chemical change so that you no longer have what you had.
What is the difference between a compound and a mixture?
A mixture can be physically separated into its components; a compound cannot be physically separated into its components.
Which has the most atoms?
All of the above have the same number of atoms
How does a suspension differ from a solution?
Although a solution and suspension are both homogeneous mixtures, only the components of a suspension will separate by spinning the mixture in a centrifuge
How is the solubility of a gas affected by temperature?
As temperature goes down, the solubility goes up.
At 10°C, which is more concentrated-a saturated solution of sodium nitrate, NaNO3, or a saturated solution of sodium chloride? (See figure shown above )
At 10°C a saturated solution of sodium nitrate, NaNO3, is more concentrated than a saturated solution of sodium chloride, NaCl.
Account for the observation that ethyl alcohol, C2H5OH, dissolves readily in water but dimethyl ether, CH3OCH3, which has the same number and kinds of atoms, does not.
Because dimethyl ether lacks an -OH group, it is significantly less polar than is ethyl alcohol and is not readily soluble in water.
Which of the above might best describe how soap behaves in a nonpolar solvent like turpentine?
C
Rank the following solutions in order of increasing concentration: solution A, 0.5 mole of sucrose in 1.0 L of solution; solution B, 1.0 mole of sucrose in 2.5 L of solution; solution C, 1.5 moles of sucrose in 4.0 L of solution.
C B A
Which of the following might have the lowest solubility in water?
CH3CH3
Which of the following might have the best solubility in water?
CH3OH
The ratio of water molecules to pesticide molecules in the glass is so great that drinking the water is not problematic.
Compared to the billions and billions of water molecules, a thousand molecules of something else is practically nothing.
What statement best describes a mole?
It is a very large number chemists use to count atoms or molecules
Which of the following describes the term concentration?
It is the amount of solute in a given amount of solution.
If water is added to 1 mole of sodium chloride in a flask until the volume of the solution is 1 L, what is the molarity of the solution?
M = 1 M
What is the molarity when water is added to 2 moles of sodium chloride to make 0.5 L of solution?
M = 4 M
Why are noble gases infinitely soluble in noble gases?
Noble gases can be mixed homogeneously in any proportion.
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
Suggest why sodium chloride, NaCl, is insoluble in gasoline. Consider the electrical attractions.
Salt is composed of ions that are too attracted to themselves. Gasoline is non-polar so salt and gasoline will not interact very well.
Many solvents expand to occupy greater volumes with increasing temperature. What happens to the concentration of a solution made with such a solvent as its temperature is increased?
Since concentration depends on how much mass is dissolved in a given volume, as the volume increases, the concentration decreases.
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.
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 synthetic
How are intermolecular forces and solubility related?
Solubility depends on the solvent's ability to overcome the intermolecular forces in a solid.
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 hot 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.
What is the difference between a compound and a mixture?
The components of a mixture are not chemically bonded together
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.
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 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 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.
From the schematic above: 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 can be said about drinking water that is 99.9999 percent free of some poison, such as a pesticide?
The ratio of water molecules to pesticide molecules in the glass is so great that drinking the water is not problematic.
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.
Why can't the elements of a compound be separated from one another by physical means?
Their atoms are too tightly bound to one another.
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.
Which of the following solutions is the most dilute?
They all have the same concentration.
What do chicken noodle soup and garden soil have in common?
They are both examples of heterogeneous mixtures.
Assuming that 20.0 g of sodium chloride has a volume of 7.50 mL, find what a volume of water will she need to make this solution. In making this solution, should she add the solute to the solvent or the solvent to the solute?
V = 1.99 L the solvent to the solute
Why isn't distillation used commercially to purify water?
Water requires large amounts of energy to boil affordably.
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.
Fatty acid molecules can also align to form a bilipid layer that extends in 3-dimensions. Shown below is a cross section of this structure. What is this structure called? (Hint: it forms the basis of all life)
a cell
Allowing water to cascade or bubble in a fountain during the purification process is an example of ________.
a gas dissolving in a liquid
How would you classify the following material? a cappuccino (with foam)
a heterogeneous mixture
Water being purified using aluminum salts and a base is an example of ________.
a physical separation
How would you classify the following material? coffee (black)
a solution
How would you classify the following material? coffee (with milk)
a suspension
How would you classify the following material? milk
a suspension
Which of the following is a mixture?
air
Which of the following picture might best describe a soap or detergent?
b
Which of the following is a pure substance?
baking soda
Which of the following might best describe the product obtained from soap and hard water (i.e., soap scum)?
c
Many dry cereals are fortified with iron, which is added to the cereal in the form of small iron particles. How might these particles be separated from the cereal?
collect the iron filings with a magnet
A combination of two or more substances in which they no longer retain their chemical properties is called a(n) ________.
compound
Classify the following as element, compound, or mixture, and justify your classifications: table salt, stainless steel, table sugar, aluminum, ice.
compound; mixture; compound element; compound
Half-frozen fruit punch is always sweeter than the same fruit punch completely melted because
crystallization is a purifying process.
Which of the above would best describe how soap behaves in water?
d
How would you classify the following material? swimming pool water
homogeneous mixture
If you filter sea water to remove all of the particles you would be left with a clear ________.
homogeneous mixture called a solution
When blue food coloring is stirred into water, the result is a ________.
homogeneous mixture called a solution
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
Based on atomic size, which would you expect to be more soluble in water: helium, He, or nitrogen, N2?
n atoms are bigger and so nitrogen molecules should be more soluble in water due to greater dipole-induced dipole attractions.
In a solution of 77 percent nitrogen and 23 percent oxygen, which is the solvent?
nitrogen
Assume the total number of molecules in a sample of liquid is about 4 million trillion. One million trillion of these are molecules of some poison, while 3 million trillion are water molecules. What percentage of all the molecules in the glass are water?
nwater = 75 %
Which of the following best describes a two-molar sucrose solution?
one liter of solution that contains 2 moles of sucrose
Which of the following solutions is the most dilute?
one liter of water with 1 gram of sugar
Which of the following solutions is the most concentrated?
one liter of water with 10 grams of sugar
Which of the following would be considered a heterogeneous mixture?
salad dressing
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
What is molarity?
the number of moles of solute per liter of solution
What is the purpose of treating water with chlorine gas or ozone during water purification?
to kill bacteria
Which of the following would be considered a homogeneous mixture?
wine