Chemistry: Solutions

Question 1

Solutions

Answer 1

Homogenous mixtures of substances that combine to form a single phase, generally the liquid phase. Many important chemical reactions, both in the lab and in nature, take place in solution (including almost all reactions in living organisms).

Question 2

Solvent

Answer 2

Component of the solution whose phase remains the same after mixing. If the solute and solvent are already in the same phase, the solvent is the component present in greater quantity.

Question 3

Solvation

Answer 3

The interaction between solute and solvent molecules. Also known as dissolution. Solvation is possible when the attractive forces between solute and solvent are stronger than those between the solute particles. For nonionic solutes, solvation involves van der Waals forces between the solute and solvent molecules. The general rule is that like dissolves like: ionic and polar solutes are soluble in polar solvents, and nonpolar solutes are soluble in nonpolar solvents.

Question 4

Hydration

Answer 4

When water is the solvent. Resulting solution is known as an aqueous solution.

Question 5

Solubility

Answer 5

Solubility of a substance is the max amount of that substance that can be dissolved in a particular solvent at a particular temperature.

Question 6

Saturated

Answer 6

When the maximum amount of solute has been added, the solution is in equilibrium and is said to be saturated; if more solute is added, it will not dissolve.

Question 7

Dilute

Answer 7

A solution in which the proportion of solute to solvent is small.

Question 8

Concentrated

Answer 8

A solution in which the proportion of solute to solvent is large.

Question 9

Crystallization

Answer 9

When a dissolved solute comes out of solution and forms crystals.

Question 10

Supersaturated Solutions

Answer 10

Solutions that contain more solute than found in a saturated solution. In a supersaturated solution, the addition of more solute will cause the excess solute in the supersaturated solution to separate, and a saturated solution will subsequently form.

Question 11

Aqueous Solutions

Answer 11

Most common class of solutions, in which the solvent is water. In discussing chemistry of aqueous solutions, its useful to know how soluble various salts are in water.

Question 12

Solubility Rules: Alkali Metals

Answer 12

All salts of alkali metals are water soluble.

Question 13

Solubility Rules: Ammonium Ion

Answer 13

All salts of the ammonium ion (NH4+) are water soluble.

Question 14

Solubility Rules: Chlorides, Bromides, and Iodides

Answer 14

All chlorides, bromides, and iodides are water soluble, with the exceptions of Ag+, Pb+2, and Hg2+2.

Question 15

Solubility Rules: Sulfate Ion

Answer 15

All salts of the sulfate ion (SO4-2) are water soluble, with the exceptions of Ca+2, Sr+2, Ba+2, and Pb+2.

Question 16

Solubility Rules: Metal Oxides

Answer 16

All metal oxides are insoluble, with the exception of the alkali metals and CaO, SrO, and BaO, all of which hydrolyze to form solutions of the corresponding metal hydroxides.

Question 17

Solubility Rules: Hydroxides

Answer 17

All hydroxides are insoluble, with the exception of the alkali metals and Ca+2, Sr+2, and Ba+2.

Question 18

Solubility Rules: Carbonates, Phosphates, Sulfides, Sulfites

Answer 18

All carbonates (CO3-2), phosphates (PO4-3), sulfides (S-2), and solfites (SO3-2) are insoluble, with the exception of the alkali metals and ammonium.

Question 19

Nomenclature of Ionic Compounds: Multiple Positive Ions

Answer 19

For elements (usually metals) that can form more than one positive ion, the charge is indicated by a Roman numeral in parentheses following the name of the element.

• Fe+2 Iron (II)
• Fe+3 Iron (III)

An older but still commonly used method is to add the ending -ous or -ic to the root of the Latin name of the element to represent the ions with lesser or greater charge, respectively.

• Fe+2 Ferrous
• Fe+3 Ferric
• Cu+ Cuprous
• Cu+2 Cupric

Question 20

Nomenclature of Ionic Compounds: Monoatomic Anions

Answer 20

Monatomic anions are named by dropping the ending of the name of the element and adding -ide.

• H- Hydride
• F- Fluoride
• O-2 Oxide

Question 21

Nomenclature of Ionic Compounds: Multiple H+ Ions

Answer 21

Polyatomic anions often gain one or more H+ ions to form anions of lower charge. The resulting ions are named by adding the word hydrogen or dihydrogen to the front of the anion’s name. An older method uses the prefix bu- to indicate the addition of a single hydrogen ion.

• HCO3- Hydrogen carbonate or bicarbonate
• HSO4- Hydrogen sulfate or bisulfate
• H2PO4- Dihydrogen phosphate

Question 22

Oxyanions

Answer 22

Many polyatomic anions contain oxygen and are therefore called oxyanions.

When an element forms two oxyanions, the name of the one with less oxygen ends in -ite and the one with more oxygen ends in -ate.

• NO-2 Nitrite
• NO-3 Nitrate
• SO3-2 Sulfite
• SO4-2 Sulfate

When the series of oxyanions contains four oxyanions, prefixes are also used. Hypo- and per- are used to indicate less oxygen and more oxygen, respectively.

• ClO- Hypochlorite
• ClO2- Chlorite
• ClO3- Chlorate
• ClO4- Perchlorate

Question 23

Electrolytes

Answer 23

The electrical conductivity of aqueous solutions is governed by the presence and concentration of ions in solution. Therefore, pure water doesn’t conduct an electrical current well since the concentrations of hydrogen and hydroxide ions are very small.

Solutes whose solutions are conductive are called electrolytes.

Question 24

Strong Elecrolyte

Answer 24

Strong electrolytes include ionic compounds, such as NaCl and KI, and molecular compounds with high polarity covalent bonds that dissociate into ions when dissolved, such as HCl in water.

Question 25

Weak Electrolyte

Answer 25

A weak electrolyte, on the other hand, ionizes or hydrolyzes incompletely in aqueous solution, and only some of the solute is present in ionic form. Examples include acetic acid and other weak acids, ammonia and other weak bases, and HgCl2.

Question 26

Nonelectrolyte

Answer 26

Many compounds do not ionize at all in aqueous solution, retaining their molecular structure in solution, which usually limits their solubility. These compounds are called nonelectrolytes and include many nonpolar gases and organic compounds, such as oxygen and sugar.

Question 27

Units of Concentration

Answer 27

Concentration denotes the amount of solute dissolved in a solvent. The concentration of a solution is most commonly expressed as percent composition by mas,s mole fraction ,molarity, molality, or normality.

Question 28

Percent Composition by Mass

Answer 28

The mass of the solute divided by the mass of the solution, multiplied by 100.

Question 29

Mole Fraction

Answer 29

Equal to the number of moles of the compound divided by the total number of moles of all species within the system. The sum of the mole fractions in a system will always equal 1. Xb = moles of b/sum of moles of all compounds

Question 30

Molarity

Answer 30

The number of moles of solute per liter of solution. Solution concentrations are usually expressed in terms of molarity. Molarity depends on the volume of the solution, not on the volume of solvent used to prepare the solution.

Question 31

Molality

Answer 31

Number of moles of solute per kilogram of solvent. For dilute aqueous solutions are 25 degrees celsius, the molality is approximately equal to the molarity, because the density of water at this temperature is 1 kilogram per liter. But note that this is an approximation and true only for dilute aqueous solutions.

Question 32

Normality

Answer 32

Equal to the number of gram equivalent weights of solute per liter of solution. A gram equivalent weight, or equivalent, is a measure of the reactive capacity of a molecule.

To calculate, we must know what purpose the solution is being used for, because it’s the concentration of the reactive species with which we are concerned.

Normality is unique among concentration units in that it’s reaction dependent. For example, a 1-molar solution of sulfuric acid would be 2 normal for acid-base reactions (because each mole of sulfuric acid provides 2 moles of H+ ions) but is only 1 normal for a sulfate precipitation reaction (because each mole of sulfuric acid provides only 1 mole of sulfate ions).

Question 33

Dilution

Answer 33

A solution is diluted when solvent is added to a solution of high concentration to produce a solution of lower concentration. The concentration of a solution after dilution can be determined by this: MiVi = MfVf where M is molarity, V is volume, and the subscriptes i and f refer to initial and final values, respectively.

Question 34

Solution Equilibria

Answer 34

The process of solvantion tends toward an equilibrium. Immediately after solute has been introduced into a solvent, most of the change taking place is dissociation, because no dissolved solute is initially present. However, according to Le Chatelier’s principle, as solute dissociates, the reverse reaction (precipitation of the solute) also beings to occur. Eventually, an equilibrium is reached, with the rate of solute dissociation equal to the rate of precipitation, and the net concentration of the dissociated solute remains unchanged regardless of the amount of solute added. An ionic solid introduced into a polar solvent dissociates into its component ions. The dissociation of such a solute in solution may be represented by AmBn(s) mA^n+(aq) + nB^m-(aq) AgCl(s) Ag+(aq) + Cl-(aq)

Question 35

Solubility Product Constant

Answer 35

A slightly soluble ionic solid exists in equilibrium with its saturated solution. In the case of AgCl, for example, the solution equilibrium is as follows AgCl(s) <–> Ag+(aq) + Cl-(aq)

The ion product (I.P.) of a compound in solution is defined as follows I.P. = [A^n+]m[B^m-]n The same expression for a saturated solution at equilibrium defines the solubility product constant Ksp = [A^n+]m[B^m-]n in a saturated solution. However, IP is defined WRT initial concentrations and doesn’t represent either an equilibrium or a saturated solution, while Ksp does; at any point other than at equilibrium, the ion product is often referred to as Qsp. Each salt has its own distinct Ksp, at a given temperature.

If at a given temperature salt’s IP is equal to its Ksp, the solution is saturated. If IP > Ksp, the solution is supersaturated. If IP < Ksp, the solution is unsaturated, no precipitate will form.

Question 36

Factors Affecting Solubility

Answer 36

The solubility of a substance varies depending on the temperature of the solution, the solvent, and in the case of a gas-phase solute, the pressure.

Solubility is also affected by the addition of other substances to the solution. The solubility of a salt is considerably reduced when it’s dissolved in a solution that already contains one of its ions, rather than in a pure solvent. For example, if a salt such as CaF2 is dissolved in a solution already containing Ca+2 ions, the dissociation equilibrium will shift toward the production of the solid salt. This reduction in solubility, called the common ion effect, is another example of Le Chatelier’s principle.