chem 20 unit 4

to form a hydrogen ion

-consider the most common isotope of the hydrogen atom which contains one proton, one electron and no neutrons -atom loses one electron -this leaves just a proton in the nucleus of the ion

Calculating [OH-]

10^-pOH

autoionization

The process by which a molecule (usually water) spontaneously dissociates into cations and anions. careful experiments on the electrical conductivity of pure water have shown that water self ionizes to a very small extent to form hydronium and hydroxide

indicator abbreviations

To represent the two forms an indicator may have, use abbreviations: HIn(aq) represents the form with low pH In¯(aq) represents the form with high pH.

arrhenius acid and base reaction or neutralization

a neutralization or double replacement reaction between an arrhenius acid and base arrhenius acid + arrhenius strong base -> a salt + water arrhenius acid is not always strong so always have to look for net ionic equation

modified arrhenius base

a strong base is a metal hydroxide compound that dissociates to form hydroxide ions and a weak base reacts partially with water to form hydroxide ions

polybasic or polyprotic base

a weak base that react with water more than once in general each successive base is weaker

arrhenius base

according to the arrhenius theory a base is a substance that dissociates to form hydroxide ions in aqueous solution which are strong bases

triprotic acid

an acid able to donate three protons per molecule (H3X(aq))

modified arrhenius acid

an acid is any substance that reacts with water to form the hydronium ion, H3O+

diprotic acid

an acid that can donate two protons per molecule (H2X(aq))

polyprotic acid

an acid that form more than one hydrogen ion in general each successive acid from a polyprotic acid is a weaker acid

problem with arrhenius base

an arrhenius base was defined as a substance that dissociates to produce hydroxide ions in aqueous solutions however this theory does not explain the basic behavior of weak bases that do not contain hydroxide ions that dissociate from the substances

indicators

are intensely colored complex organic weak acids and bases

function of indicators

are used to determine the pH of a solution

strong acids vs weak acids

completely react with water while a weak acid partially reacts with water to form hydronium ions strong acids use a one way arrow weak acids use a one way arrow and <50% over the arrow or use a two way arrow

the original arrhenius theory

did not consider the hydronium ion

pH values

dont have units since the formula deals with the numerical part of the {H3O+} and you cannot take the logarithum of the unit mol/L

The Acid-Base Indicator table + example

gives the range of pH values over which different indicators change color. Example: methyl red changes color between a pH of 4.8 and 6.0. Methyl red is red when pH greater than 4.8 Methyl red is yellow when pH less than 6.0 Between 4.8 and 6.0 the colour is a blend of red and yellow.

a few years after arrhenius work on the theory of electrolytes

he proposed a theory to explain the behavior of acids and bases

arrhenius acid

is a substance that produces the hydrogen ion or proton H+ in aqueous solution.

the hydrogen ion

is also referred to as a proton

pOH formula

is less common but is calculated in a similiar way to the calculation of pH pOH = -log{OH-}

modern days acids

now we know that bare protons become hydrated in aqueous solution to form the hydronium ion H3O+

monoprotic acid

one proton to donate (HX(aq)

significant digits in a pH value

only the digits that follows the decimal place are significant in a pH value

relashinship between pH and pOH

pH + pOH = 14

monobasic or monoprotic base

produces 1 OH

dibasic or diprotic base

produces 2 OH

tribasic or triprotic base

produces 3 OH

concentration of OH- and H3O+

ranges from 1.0 x 10 to the power of -14 mol/L to 1.0 x 10 to the power of 0 this represents a 10 to the power of 14 times difference in concentration and often you are dealing with very low concentrations

the pOH scale

similar to the pH representing the power of hydrogen ion a value referred to pOH represents the power of the hydroxide ions in an solution

in 1909

soren sorensen proposed the pH scale ad a more convenient way to deal with the small concentration of OH- and H3O+ found in many aqueous solutions

If an acid has COOH + example

the H in the COOH is the only H atom that can react with water. CH3COOH is monprotic. HOOCCOOH is diprotic

pH

the power of hydrogen ion is defined as pH = -log{H3O+}

if concentration of hydroxide is lower than the concentration of hydronium

then the solution is acidic

if concentration of hydroxide is greater than the concentration of hydronium

then the solution is basic

if the concentration of hydronium is equal to the concentration of hydroxide

then the solution is neutral

notation

use a lower case for p and an upper case for H when ever writing pH

because of autonization

we can assume that all dilute aqueous solutions contain both concentrations of hydroxide and hydronium ions

finding the concentration of H3O+ formula

{H3O+} = 10 to the power of -pH