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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