chapter 4 - reactions in aqueous solutions

solutions

homogenous mixture of 2 or more pure substances

in a solution, ___ is present in the greatest abundance

solvent

aqueous solution

when water is the solvent

how do substances dissolve?

by solvation: surrounding of the solute by solvent

dissolution of ionic compounds

dissociation - water surrounds separated ions

dissolution of molecular compounds

may disperse in water, but most remain intact - some form ions in water when dissolved

solubility rules of ionic compounds

used to decide what combination of ions will dissolve

electrolytes

a substance that dissociates into ions when dissolved in water

strong electrolytes

• dissociate completely when dissolved in water

• solution conducts electricity

• chemical equation has single arrow

weak electrolytes

• partially dissociates when dissolved in water

• chemical equation has double arrow (f    ) which indicates a chemical equilibrium

nonelectrolytes

• do not dissociate in water

• solution does not conduct electricity

precipitation reactions

occur when 2 or more solutions containing soluble salts are mixed and an insoluble salt is produced; solid(s) is called a precipitate

metathesis (exchange) reactions

anions in the reactant compounds exchange

acids

substances that ionize in aqueous solutions to form hydrogen ions (H+)

bases

substances that react with, or accept, H+ - increase hydroxide ions (OH-) when dissolved in water

strong acids

completely dissociate in water

weak acids

partially dissociate in water

strong bases

dissociate metal cations and hydroxide anions in water

weak bases

partially react to produce hydroxide anions

all ionic substances are ___ ___

strong electrolytes

molecular substance - ___ acids are ___ electrolytes

strong

molecular substance - ___ acids and ___ bases are ___ electrolytes

weak

molecular substance - all other compounds are ___

nonelectrolytes

neutralization reactions

reactions between an acid and a base

when the base is a metal hydroxide…

…water and a salt (ionic compound) are produced

when a carbonate or bicarbonate reacts with an acid…

…a salt, carbon dioxide, and water are produced

oxidation =

= loss of electrons

reduction =

= gain of electrons

oxidation numbers

we assign an oxidation number to each element in a neutral compound or charged entity to determine if an oxidation-reduction reaction has occurred

rules to assign oxidation numbers

1. atoms in their elemental form have an oxidation number of 0

2. the oxidation number of a monoatomic ion is the same as its charge

3. nonmetals usually have negative oxidation numbers; sometimes they can be positive

4. sum of oxidation numbers in a neutral compound is 0; the sum of the oxidation numbers in a polyatomic ion is the charge on the ion

monoatomic elements

+1: H, Li, Na, K

+2: Be, Mg, Ca

+3: B, Al, Ga

+4: C, Si, Ge

-1: F, Cl, Br, I

-2: O

-3: N

peroxide ion

-1

hydrogen

+1 when bonded to a nonmetal; -1 when bonded to a metal

halogens

usually -1; oxyanions will be positive

displacement reactions

oxidation of metals by acids and salts - ions oxidize an element

activity series and hydrogen

elements above hydrogen will react with acids to produce hydrogen gas; elements below will not react

if oxidation number increases, element is ___

oxidized

if oxidation number decreases, element is ___

reduced

concentration

the amount dissolved in a solution

molarity (M)

a way to measure the concentration of a solution - M = moles of solute/volume of solution in liters (mol/L)

mixing a solution of a known molarity

1. weigh out a known mass (and therefore number of moles) of solute

2. add solute to flask

3. add solvent to line on neck of flask

how can a solution be diluted?

add only solvent

finding molarity of new solution

M_c x V_c = M_d x V_d

• Mc = molarity of concentrated solution

• Md = molarity of dilute solution

• Vc = volume of concentrated solution

• Vd = volume of dilute solution