MODULE 2 – EQULIBRIUM CHEMISTRY

Mole

Even the smallest samples we deal with in the laboratory contain enormous numbers of atoms, ions, or molecules.

mol

abbreviated as mol

Avogadro’s number

6.022 x 10²³

atomic weight

an element in atomic mass units is numerically equal to the mass in grams of 1 mol of that element.

molar mass

is numerically equivalent to the sum of the atomic weights of all the atoms present in a compound, and has the unit g/mol.

solution

is a homogenous mixture of two or more substances whose composition may be varied within certain limits.

solute

comprises one substance

solvent

dissolved in another substance

solute

is the substance that is present in the smaller amount.

solvent

is the substance that is present in the larger amount.

water

Most chemical reactions encountered in analytical chemistry take place in aqueous solutions, those whose solvent is ?

ionic compounds and polar compounds

Because water is polar, the solutes that can dissolved in it are ? and ?.

electrolytes

Ionic compounds form ? when they dissolve in water, while polar compounds do not.

Concentration

is a general measurement unit stating the amount of solute present in a known amount of solution.

molar

symbolized by M, which has the dimensions of mol/L.

Percent Composition

parts per million

parts per billion

Density and specific gravity

are related terms often found in the analytical literature.

density

of a substance is its mass per unit volume

specific gravity

the ratio of its mass to the mass of an equal volume of water at 4°C.

kilograms per liter or grams per milliliter

Density has units of

irreversible

Most chemical reactions are

microscopic scale

On a ______________, most chemical reactions are reversible which means it can occur both in the forward and backward directions.

reversible

Many reactions used in analytical chemistry never result in complete conversion of reactants to products ?

chemical equilibrium

Reversible reactions often proceed to a state of _____________ in which the ratio of concentrations of reactants and products is constant.

mass-action effect

An equilibrium shift brought about by changing the amount of one of the participating reactants or products is called a

equilibrium-constant expression

The influence of concentration on the position of a chemical equilibrium is conveniently described in quantitative terms by means of an ?

equilibrium constant

The constant K in in the equilibrium constant expression is a temperature-dependent numerical quantity called the

Kw

Ion-product constant

Ka or Kb

Dissociation constant

Slightly soluble compounds

are those that has a solubility in water of less than 0.020 mol/L.

solubility product expression

for a compound is the product of the concentration of its constituent ions, each raised to the power that corresponds to the number of ions in one formula unit of the compound.

Solubility

amount of compound that dissolves in a specified volume of solution. This is

usually expressed as g/L or g/100 mL.

Molar solubility

number of moles of a compound that dissolve to give 1 L of saturated solution. This is expressed as mol/L.

common ion effect

When a solution of a slightly soluble salt is added with one of its ions from another source, the solubility of that salt is reduced. This is known as the ?

solubility product constant (Ksp)

a constant that describes the extent to which a slightly soluble salt dissolves in water, by expressing the concentration of the ions in a saturated solution (at equilibrium).

fractional precipitation

We sometimes wish to remove selected ions from solution while leaving others with similar properties in solution. This separation process is called ?

The reaction shifts to the left.

Backward reaction is favored; thus, more reactants are produced.

The reaction shifts to the right.

Forward reaction is favored; thus, more products are produced.

mass-action effect

An equilibrium shift brought about by changing the amount of one of the participating reactants or products

thermodynamics

They are important because they allow us to predict the direction and completeness of chemical reactions.

less than

If K is small, (K<1) like ________ 10^-3 a reaction yields very small products before equilibrium is reached.

like above

If K is large, (K>>1) ________ 103 very few reactants are left before equilibrium is reached.

solubility product (Ksp)

most useful in the qualitative analysis of cations.

Slightly soluble compounds

are those that has a solubility in water of less than 0.020 mol/L.