Acids, bases, and pH

Objectives

• Describe the ionization of strong acids in water and the DISSOCIATION of strong BASES in water

• Distinguish between solutions of weak acids or bases and strong acids or bases

• Relate pH to the concentration of HYDRONIUM ions in a solution

What are acids

ACIDS

• Acid – any compound that INCREASES the number of HYDRONIUM ions when dissolved in water

• Example : H2O + HCl H3O+ + Cl-

• Acids will IONIZE in water = form ions see above example

• Acids will turn BLUE litmus paper RED

Common acids

• Common examples of acids –

• citrus fruits

• Formic acid – an acid found in stinging ants HCOOH

• Vinegar = acetic acid CH3COOH

• Hydrochloric acid – HCl

• Nitric acid HNO3

Acids IONIZE

• When an acid is dissolved in water the Hydrogen from the acid forms a bond with a water molecule to form a HYDRONIUM ION and the anion from the acid

• Example : H2O + HCL H3O+ + Cl-

• H2O + CH3COOH H3O+ + CH3COO-

• • A double arrow in an equation indicates

that the reaction goes in both directions

• Weak acids DO NOT ionize completely• A double arrow indicates that the ions

quickly go back to the original acid and water

• Weak acids are POOR ELECTROLYTES• A STRONG acid DOES ionize completely

indicated by a single arrow• Strong acids are GREAT

ELECTROLYTES

• STRONG ACIDS conduct electricty = Electrolyte – a light bulb will glow brightly

• Weak Acids are POOR Electrolytes

• A light bulb will BARELY glow

http://www.youtube.com/watch?v=a21kuzQW7AE

Indicators

• A compound that can reversibly change color depending on the pH of the solution

• Litmus paper – Identifies if a solution is an acid or a base

• An acid turns blue litmus paper RED• A base turns red litmus paper blue• pH paper – will determine the pH of the

solution from a range of pH1(strong acid) red through pH14 (strong base) blue

Acids are dangerous in concentrated form

• Concentrated acids damage human tissue• Acetic acid = vinegar sold in 5% solution

b/c concentrated acetic acid(glacial) damages tissue and the vapors damage tissues of the eyes, mouth, lungs

• Stomach acid = pH 2 which damages tissue outside of the stomach – when a person “throwsup” the mucus lining of their throat and nose is “burned”

BASES

• Any compound that increases the number of HYDROXIDE ions when dissolved in water

• Example: Strong bases

• NaOH + H2O Na+ + OH- + H2O

• KOH + H2O K+ +OH- + H2O

• Strong ELECTROLYTES

WEAK BASES

• Do minimally increase the OH-

• Do not dissociate completely in water• The water acts like an ACID by donating

the hydrogen ion• NH3 + H2O NH4

+ + OH-

• • Ammonia becomes ammonium ion

• CH3NH2 + H2O CH3NH3+ + OH-

• • Just as in the weak acid the “double

arrow” in the equation means the reaction is going in both directions

• Weak Electrolyte – since the ions form and then reform into noncharged molecules again

pH scale

• http://www.alternativemedicinedirect.com/NewSiteImages2011/phscalergb.jpg

pH power of hydronium

• A value used to express the acidity or alkalinity(base) of a solution

• Negative logarithm• Logarithm = exponent• Example:• If the concentration of H3O+ = 1x10-2

• The exponent = -2• The “NEGATIVE” of -2 = 2• The pH then =2

WATER

• Because water dissociates the concentration of H3O+ equals the concentration of OH-

• The total concentration of H3O+ and OH-

ions = 1x10-14

• H3O+ = 1x10-7

• OH- = 1x10-7

How pH tells us acidity

• If the pH of a solution = 1x10-1 then the amount of H3O+ = .1

• If .1 was money = 10 cents

• I

• If the pH of a solution was 1x10-2 then the H3O+ concentration = .01

• If .01 was money = one penny

• Which value is MORE acidic – pH1 or pH2

• Which is more money a dime or a penny

• If the concentration of H3O+ = .0000000000001 then the pH = 1x10-13

• You would need a WHOLE lot of these to just equal ONE PENNY!

• There are VERY little H3O+ ions in solution!

• How many OH- ions will be in this solution?

Calculating OH- ions via pH

• H3O+ + OH- = 1x10-14

• If H3O+ = 1x10-13 then• 1x10-13 + OH- = 1x10-14 then • OH- = 1x10-1

• 1x10-1(OH-) = .1 (a dime)• 1x10-13(H3O+) = very very very very little• So there are MUCH more OH- • pH13 solution is a very strong BASE

8-2 Reactions with acids and bases

• Objectives:

• Write ionic equations for neutralization reactions

• Identify the products of neutralization reactions

• Describe the composition of a salt

Neutralization Reactions

• Reactions with Acids and Bases

Examples

• AB + CD AD + BC

• The cation of the first compound will form a new bond with the anion of the second compound

• The cation of the second compound will form a bond with the anion of the first compound

• HCl + NaOH HOH + NaCL

• Notice HOH = H2O

• A strong acid (HCl) reacts with a strong Base (NaOH) to form water and a salt

• ALWAYS!!!!! Any strong acid any strong base reacts to from water and a salt

• WATER is NEUTRAL pH =7

• Thus “Neutralization” reaction

WHAT ARE SPECTATOR IONS

• Spectator = a bystander of an event

• Wouldn’t we all love to be a spectator in LONDON this summer for the olympics?

• Spectator ions are the ions that will eventually form the salt

• HCl + NaOH Na+ + Cl- + H2O

• H2SO4 + KOH K+ + SO4- + H2O

• In both reactions, once the water evaporates the salts will form NaCl and K2SO4

NOT all Neutralization reactions form salts.

• Weak acid + Strong base weak base no water still too many OH- ions in solution

• Strong acid + Weak Base weak acid no water still too many H3O+ ions in solution

• Our body has Natural “buffers” to prevent our blood from being TOO acidic or TOO basic

• H+aq + HCO-

3aq H2CO3aq H2OL+ CO2g

8-3 Acids, Bases, Salts in the home