9.2 solution of Electrolytes and Nonelectrolytes

Of the following, which are electrolytes?

-All of the above Soluble ionic compounds, strong acids, and weak bases are all electrolytes of varying strength. This is because they will all dissociate into ions to some degree in aqueous solutions. Nonelectrolytes are typically covalently bonded molecules that do not dissociate into ions.

True or False? In solid form, an ionic compound is electrically conductive.

-False In solid form, an ionic compound is not electrically conductive because its ions are unable to flow (electricity is the flow of charged particles). When molten, however, it can conduct electricity because its ions are able to move freely through the liquid.

Which of the following occurs when an ionic compound dissolves in a polar solvent such as water?

-The water molecules attract both the anions and cations in the ionic salt. -The ions become solvated water molecules, which reduces the electrostatic attractions between the ions. When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic attractions between them. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.

Which of the following are not true of covalent electrolytes?

-They may contain ions. -All soluble covalent compounds are covalent electrolytes. Covalent electrolytes, by definition, must be entirely covalent compounds that contain no ions themselves; they merely yield ions in solution. Moreover, not all covalent compounds will yield ions when dissolved in water. Some, like sugar, will not react with water to produce ions to any appreciable extent.

Which of the following is a characteristic of weak electrolytes?

-They produce a low concentration of ions when dissolved in water. Weak electrolytes exhibit low (but still some) conductivity and produce a low concentration of ions when dissolved in water. Strong electrolytes exhibit high conductivity and produce a high concentration of ions when dissolved in water (choices a and d) and nonelectrolytes exhibit no conductivity (choice b).

Which of the following are generally weak electrolytes?

-Weak bases -Weak acids Weak acids and weak bases are generally weak electrolytes as they do not dissociate completely in aqueous solutions. Strong acids and bases dissociate completely into their ions.

Acetic acid, CH3COOH, is a weak acid. We can conclude that CH3COOH is also:

-a weak electrolyte Since CH3COOH is a weak acid, we can conclude that it only reacts with water to produce ions to a limited extent. Thus acetic acid is both a weak acid and a weak electrolyte.

When electrolytes are dissolved in water, they undergo:

-either of the above When some substances (electrolytes) are dissolved in water, they undergo either a physical or a chemical change that yields ions in solution. If the physical or chemical process that generates the ions is essentially 100% efficient (all of the dissolved compound yields ions), then the substance is known as a strong electrolyte. If only a relatively small fraction of the dissolved substance undergoes the ion-producing process, it is called a weak electrolyte.

When the electrostatic attractions between the ions in a crystal are so large that the increase in disorder cannot compensate for the energy required to separate the ions, the crystal is ________.

-insoluble Insoluble crystals have electrostatic attractions (between the ions) that are stronger than the energy available to separate the ions.

What types of interactions occur between ions and water molecules that promote the dissolution process?

-ion-dipole The dipoles on the water molecules will interact with the formally charged ions to produce ion-dipole interactions.

Which substance, when dissolved in water, will conduct the most electricity?

-potassium chloride Potassium Chloride (KCl) is the only strong electrolyte among the options, so it will conduct the most electricity. Ethanol is a nonelectrolyte. Both ammonia and acetic acid are weak electrolytes.

Dissolution occurs because:

-the cations and anions will make ion-dipole interactions with the solvent When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic attractions between them. This process represents a physical change known as dissociation.

Electrolyte

A substance that dissolves in water to give a solution that conducts electric current; a substance that when dissolves in water will product ions and conduct electricity

Why do ionic compounds not conduct electricity in their crystalline form

Electricity can only be conducted when ions are moving. Electricity can only be conducted when ions are moving. In their crystalline form, the ions in the ionic compound are locked tightly in one place.

A compound has a melting point of 545 degrees Celsius and dissolves well in water. Why?

The high melting point points toward an ionic compound, though the fact that it dissolves is irrelevant. The high melting point points toward an ionic compound, though the fact that it dissolves is irrelevant. Most ionic compounds are solids that typically melt at high temperatures and boil at even higher temperatures.

Which of the following is not true of ionic electrolytes?

They may be covalent compounds before dissolution. Covalent compounds are not ionic compounds; therefore they cannot be considered ionic electrolytes.

Identify the option below that is not true of ionic electrolytes.

They must be completely soluble in water. Ionic electrolytes include slightly soluble ionic compounds as well: although these do not dissolve in water completely, the small amount that does dissolve also dissociates to produce ions in water.

strong electrolyte

a solution in which a large portion of the solute exists as ions; completely dissolves in water

weak electrolyte

a solution that conducts electricity poorly because only a fraction of the solute exists as ions; some partials dissociate and some particles don't when in water; still conduct electricity but not as much

non-electrolyte

a substance that will not dissociate when dissolve in water

Covalent electrolytes are typically:

depends on the substance Covalent electrolytes can be strong or weak, depending on the strength of the acid or base. Strong acids and bases are typically strong electrolytes. Nonelectrolytes do not dissociate into ions in solution; nonelectrolyte solutions do not, therefore, conduct electricity.

Dipole-dipole attractions:

form between partially positive ends of one polar molecule and partially negative ends of another Dipole-dipole attractions form between partially positive ends of one polar molecule and partially negative ends of another.

As an ionic solid dissociates, disorder

increases The change from a fixed crystalline state to a mobile state will always mean an increase in disorder or entropy.

The process by which ionic solids dissociate into respective ions is a

physical process The process by which ionic solids dissociate into respective ions is a physical process as it does not chemically change the substance.

When sodium hydroxide NaOH dissociates in water, the oxygen atoms on the hydroxide anions will interact with:

the positive end of water's dipole Hydroxide ions ( OH−) are negatively charged, and the formal negative charge is on the oxygen atom. Since opposite charges attract, the oxygen atoms will interact with the positive end of water's dipole.

Which best describes the dipole-dipole attractions? They are specifically the interaction between

two formal, or permanent, dipoles As the name would suggest, these attractions occur when one formal dipole interacts with another formal dipole.