Acids, Bases & Redox Processes

Brønsted-Lowry acid

substance that donates a proton (H+ ion)

Brøsted-Lowry base

substance that accepts a proton (H+ ion)

conjugate acid-base pairs

two substances that differ by one proton: acid donates a proton → becomes conjugate base, base accepts a proton → becomes conjugate acid

pH-Scale

measures concentration of H+ ions in a solution

pH values

0-2: strong acid, 3-6: weak acid, 7: neutral, 8-11: weak alkali, 12-14: strong alkali

lower pH

more H+ ions, more acidic

higher pH

less H+ ions, more alkaline

pOH Scale

measures concentration of OH- ions

relationship between pH and pOH

at 25 degrees celsius: pH+pOH=14

indicators

substances that change colour depending on pH

Litmus

acid colour: red, alkali color: blue

Phenolphtalein

acid color: colorless, alkali color: pink

Methyl orange

acid color: red, alkali color: yellow

universal indicator

acid color: red/orange, alkali color: blue/purple

strong acids

completely ionize in water

weak acids

only partially ionize in water

strong/weak

describes degree of ionization

concentrated/dilute

describes amount of acid dissolved

dissociation constants (Ka)

measures acid strength

dissociation constant equation

Ka = ((H+)(A-))/(HA) HA=acid, H+=hydrogen ion, A-=conjugate base

large Ka

strong acid → ionizes more, produces more H+ ions

small Ka

weak acid

salt hydrolisis

happens when ions from salts react with water

strong acid + string base

= neutral

strong acid + weak base

= acidic

weak acid + strong base

= alkaline

oxidation

loss of electrons

reduction

gain of electrons

OIL RIG

oxidation is loss, reduction is gain

oxidation state

charge an atom would have if electrons were completely transferred

elements alone

0

group one metals

+1

group two metals

+2

usual oxidation state of oxygen

-2

usual oxidation state of hydrogen

+1

usual oxidation state of halogens

-1

oxidizing agent

causes oxidation, gains electrons, is reduced

reducing agent

causes reduction, loses electrons, is oxidized

oxidation causes

an increase in oxidation state

reduction causes

a decrease in oxidation state

rules for balancing redox equations

1. balance atoms except H and O

2. balance oxygen using H2O

3. balance hydrogen using H+

4. balance charge using electrons

5. check everything balances

Voltaic (Galvanic) Cells

produces electricity from a spontaneous redox reaction → chemical energy becomes electrical energy, electrons flow through wires, two half-cells are used

Salt Bridge

completes the circuit, allows ions to move, prevents charge build-up (keeps charge balanced)

Electrolytic Cells

uses electricity to force a chemical reaction → electrical energy becomes chemical energy, requires external power source (reaction is non-spontaneous), used in electroplating and metal extraction

electroplating

using electrolysis to coat an object with metal, reasons: improve appearance, prevent corrosion, reduce cost