Exam 3 practice problems (Mod 7, 8, 9)

Which of the following substances is pure? -None would be considered pure substances. -a covalent compound consisting of one type of molecule -an ionic compound consisting of sodium and chlorine ions -an element -All would be considered pure substances.

-All would be considered pure substances.

Which of the following describes the term concentration? It is what you are doing now to answer this question. -It is the given amount of solvent per amount of solute. -It is the given amount of solution in a given container. -It is the amount of solvent in a given amount of solution. -It is the amount of solute in a given amount of solution.

-It is the amount of solute in a given amount of solution.

Why is soap useful for removing nonpolar substances from your hands? -Soap is necessary because it has both a polar and nonpolar end to interact with the nonpolar molecules on your hands and the polar water molecules. -Soap is not useful because the nonpolar water molecules are attracted to the nonpolar molecules on your hands. -Soap is necessary because it creates a film on the surface of your skin, shielding it from interacting polar water molecules. -None of the answers are correct.

-Soap is necessary because it has both a polar and nonpolar end to interact with the nonpolar molecules on your hands and the polar water molecules.

How many moles of sugar, C12H22O11, are there in 200. grams? 1.71 moles 0.684 moles 68,400 moles 0.585 moles

0.585 moles

How many moles of sugar, C12H22O11, are there in 200. grams? 68,400 moles 0.585 moles 1.71 moles 0.684 moles

0.585 moles

A student is told to use 10.00 grams of sodium chloride to make an aqueous solution that has a concentration of 10.00 grams of sodium chloride per liter of solution. About how much water will she use in making this solution? 0.992 L 1.08 L 1.00 L

0.992 L

If you need 10. moles of sucrose, how many liters of a 4.0 molar solution would you need? 2.5 L 10. L 0.25 L 25 L None of the answers are correct.

2.5 L

How many molecules of sucrose are in a 0.500 moles of sucrose? 3.01 × 1023 molecules of sucrose 6.02 × 1023 molecules of sucrose 12.04 × 1023 molecules of sucrose 1 gram 0.5 gram

3.01 × 1023 molecules of sucrose

If the solubility of a compound is 72 grams per liter at a given temperature, how many grams of the compound will dissolve in 0.50 liters at the same temperature? 72 g None of the answers are correct. 144 g 36 g 30 g

36 g

How many moles of water are there in 100. grams of water? 0.018 moles 100 moles 5.55 moles 1800 moles

5.55 moles

How many molecules of sucrose are in 0.500 L of a 2.00 molar solution of sucrose? 0.5 gram 12.04 × 1023 molecules of sucrose 1 gram 3.01 × 1023 molecules of sucrose 6.02 × 1023 molecules of sucrose

6.02 × 1023 molecules of sucrose

Would you expect to find more dissolved oxygen in polar or tropical ocean waters? Why? A) There would be more dissolved oxygen in the polar oceans because the solubility of oxygen in water decreases with increasing temperature. B) There would be more dissolved oxygen in the polar oceans because the colder oxygen would "sink" and dissolve into the water. C) There would be more dissolved oxygen in the tropical oceans because intense tropical storms mix up the atmospheric oxygen into the ocean water. D) There would be more dissolved oxygen in the tropical oceans because the heated oxygen molecules in the air would collide with and mix into the water.

A) There would be more dissolved oxygen in the polar oceans because the solubility of oxygen in water decreases with increasing temperature.

*In which of the following molecules will water induce a temporary dipole? None of the molecules. N2 CO2 All of the molecules. O2

All of the molecules.

Which of the following material phases cannot form a solution? Only liquids and gases can form solutions. solids liquids All of the phases can form solutions. gases

All of the phases can form solutions.

Which of the following material phases cannot form a solution? gases liquids solids Only liquids and gases can form solutions. All of the phases can form solutions.

All of the phases can form solutions.

Which of the following describes reverse osmosis in the desalination of water? A) High pressure saltwater is reacted with aluminum, which absorbs the sodium ions in an oxidation reaction. B) High pressure saltwater is forced against a semipermeable membrane and fresh water comes out. C) Saltwater is chemically reacted with aluminum particles, which chemically binds to the chloride ions. D)The water is heated until it evaporates and condenses in a pure form.

B) High pressure saltwater is forced against a semipermeable membrane and fresh water comes out.

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? A) Since it has a greater ability to dissolve more solute at a higher temperature, its concentration has decreased. B) Since concentration depends on how much mass is dissolved in a given volume, as the volume increases, the concentration decreases. C) Since it has a greater ability to dissolve more solute at a higher temperature, its concentration has increased. D) The concentration of a solution increases as the solute fits into the new spaces between the molecules.

B) Since concentration depends on how much mass is dissolved in a given volume, as the volume increases, the concentration decreases.

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.) A) Structure A represents the gas molecule because there are more bonds to gain energy from, giving it a higher energy content than oil. B) 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 giving the appearance of a thicker solution than gasoline. C) Structure B represents crude oil which is processed to generate longer molecules of gasoline to prevent toxic vapors from harming consumers. D) Structure B represents the oil molecule. Because oil molecules are smaller, they can compact closer together, giving the appearance of a thicker solution than gasoline.

B) 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 giving the appearance of a thicker solution than gasoline.

What happens when the molecule-to-molecule attractions in the solute are comparable to those in the solvent? A) The solute does not dissolve in the solvent. B) The solute can have infinite solubility in the solvent. C) The material has only limited solubility in the solvent. D) The solution will become saturated.

B) The solute can have infinite solubility in the solvent.

Dipole-induced dipole forces of attraction exist between water and gasoline, and yet these two substances do not mix because water has such a strong attraction for itself. Which of the following compounds might best help to make these two substances mix into a single liquid phase? A) The molecule on the right will form attractions with the polar ends of the water, allowing the gasoline a chance to mix with the water. B) the molecule on the far left because the O-H bond is polar and the carbon and hydrogen bonds are nonpolar C) the molecule in the middle because when the salts mix into the water, it will help separate the water and decrease the attraction for itself D) All of these molecules would be equally effective at increasing the mixing of gasoline and water.

B) the molecule on the far left because the O-H bond is polar and the carbon and hydrogen bonds are nonpolar

Why does oxygen have such a low solubility in water? Both of the answers are correct. Neither of the answers are correct. 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 of the answers are correct.

How can you tell whether a sugar solution is saturated or not? A) As long as there are more water molecules than sugar molecules, there is a saturated solution. B) Add more sugar, if it dissolves, it is saturated. C) Add more sugar. If it does not dissolve after mixing, the solution is saturated. D) There will be a precipitate if the water is heated.

C) Add more sugar. If it does not dissolve after mixing, the solution is saturated.

Based on atomic size, which would you expect to be more soluble in water: helium, He, or nitrogen, N2? A) He atoms are bigger and so helium molecules should be more soluble in water due to greater dipole-induced dipole attractions. Although B) He is smaller, its outer orbital is filled and the atom will have little attraction to the water molecules. C) Nitrogen atoms are bigger and so nitrogen molecules should be more soluble in water due to greater dipole-induced dipole attractions. D) Since He atoms are smaller, more of them can fit into solution, so it has a higher solubility in water.

C) Nitrogen atoms are bigger and so nitrogen molecules should be more soluble in water due to greater dipole-induced dipole attractions.

Why is soap useful for removing nonpolar substances from your hands? A) Soap is not useful because the nonpolar water molecules are attracted to the nonpolar molecules on your hands. B) Soap is necessary because it creates a film on the surface of your skin, shielding it from interacting polar water molecules C) Soap is necessary because it has both a polar and nonpolar end to interact with the nonpolar molecules on your hands and the polar water molecules. D) None of the answers are correct.

C) Soap is necessary because it has both a polar and nonpolar end to interact with the nonpolar molecules on your hands and the polar water molecules.

Which of the following molecules is most likely to show a hydrogen bonding interaction? CH3OH H-CC-H CH4 CH3SH A, B and C

CH3OH

Which of the following molecules is most likely to show a dipole-dipole interaction? CH4 CO2 SO2 H-CC-H None of the answers are correct.

CO2

Why might softened water not be good for some one who is trying to reduce their dietary sodium ion intake? A) The softened water leaches sodium from the body, so a person might not be getting the dietary recommended levels of sodium. B) A person needs a certain level of calcium and magnesium in the water to help excrete the sodium from their body. C) The potassium used in the softener to replace the calcium and magnesium ions increases the sodium retention in the body. D) Water softeners work by replacing the calcium and magnesium ions of the water with sodium ions; softened water contains increased levels of sodium ions.

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

Might reverse osmosis be used to obtain fresh water from a sugar-water solution? A) No, osmosis and reverse osmosis only apply to aqueous solutions containing ions. B) Yes, because sugar molecules are smaller than sodium or chloride ions. C) No, the molecular attractions between sugar and water are too strong. D) Yes, reverse osmosis can be applied to any aqueous solution for the generation of fresh water.

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

What is a hydrogen bond? A) a special type of dipole-dipole attraction involving hydrogen bound to another hydrogen atom B) a special type of attraction involving any molecules that contain hydrogens C) None of the answers are correct. D) a special type of dipole-dipole attraction involving hydrogen bound to a highly electronegative atom E) a special type of dipole-dipole attraction involving hydrogen bound to any other atom

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

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 amount of gas in the solution would stay the same. The pressure goes down and the gas moves out of the solvent. The pressure goes down and the gas goes into the solvent. The solution is compressed and the gas is forced out of the solvent. The gas is forced into solution and the solubility increases.

The gas is forced into solution and the solubility increases.

What is the special property of a semipermeable membrane that makes osmosis possible? -Ions only move one way through the membrane. -The pores in the membrane only allow water to pass through. -Only the ions travel through the membrane. none of the above -Water only moves through the membrane in one direction.

The pores in the membrane only allow water to pass through.

What happens when the molecule-to-molecule attractions in the solute are comparable to those in the solvent? The solute does not dissolve in the solvent. The material has only limited solubility in the solvent. The solute can have infinite solubility in the solvent. The solution will become saturated.

The solute can have infinite solubility in the solvent.

Which of the following solutions is the most dilute? 0.2 liter of water with 2 grams of sugar They all have the same concentration. 0.1 liter of water with 1 gram of sugar 0.5 liter of water with 5 grams of sugar 1 liter of water with 10 grams of sugar

They all have the same concentration.

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 gene DNA a cell a nucleoside

a cell

Water being purified using aluminum salts and a base is an example of ________. a chemical separation an acid-base reaction a chemical reaction a physical separation

a physical separation

A soap molecule is ________. both polar and nonpolar a neutral compound primarily nonpolar primarily polar

both polar and nonpolar

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 dipole-dipole molecular attractions -Ions are formed as the plastic rubs against itself. -by way of induced dipole-induced dipole molecular attractions -by way of dipole-induced dipole molecular attractions

by way of induced dipole-induced dipole molecular attractions

Hard water contains excessive amounts of ________. fluoride and sodium ions calcium and magnesium ions calcium and sodium ions magnesium and sodium ions

calcium and magnesium ions

Which of the above would best describe how soap behaves in water? a c b d

d