ACIDS AND BASES AND PH

Chemistry Acids and Bases Properties and pH

Chemical Warfare!

What is an Acid?  3 Major Definitions: Arrhenius, Bronsted-Lowry, and Lewis.  Arrhenius and Bronsted-Lowry say an acid is: A proton donor  What is a proton? A proton = H + H + = H 3 O +

Acid and Base Strength  Acids and bases are considered “strong” or “weak” depending on how much they dissociate  The more something dissociate, the stronger acid or base it is.  This means we are looking at the amount of H + or OH - is in the solution

Ionization of HCl and formation of hydronium ion, H 3 O + H 2 O + HCl  H 3 O + + Cl - Proton donor Proton acceptor

Strong Acids vs. Weak Acids Strong acids are assumed to be 100% disassociated in solution (good proton donors). Are Strong Electrolytes Weak acids are usually less than 5% disassociated in solution (poor proton donors). Are Weak Electrolytes. HClH 2 SO 4 HNO 3 H 3 PO 4 HC 2 H 3 O 2

Strong Acid Dissociation

Weak Acid Dissociation

Arrhenius & Bronsted-Lowry Acids= Proton Donors Monoprotic acidsDiprotic acidsTriprotic acids HCl HC2H3O2HC2H3O2 HNO 3 H 2 SO 4 H 2 CO 3 H 3 PO 4

Properties of Acids  Acids taste sour  Acids effect indicators  Blue litmus turns red  Methyl orange turns red  Acids have a pH lower than 7  Acids are proton (hydrogen ion, H + ) donors  Acids react with active metals, produce H 2  Acids react with carbonates, produce CO 2  Acids neutralize bases

Sulfuric Acid  Highest volume production of any chemical in the U.S.  Used in the production of paper  Used in production of fertilizers  Used in petroleum refining

Nitric Acid Used in the production of fertilizersUsed in the production of fertilizers Used in the production of explosivesUsed in the production of explosives Nitric acid is a volatile acid – its reactive components evaporate easilyNitric acid is a volatile acid – its reactive components evaporate easily Stains proteins (including skin!)Stains proteins (including skin!)

Hydrochloric Acid Used in the pickling of steelUsed in the pickling of steel Used to purify magnesium from sea waterUsed to purify magnesium from sea water Part of gastric juice, it aids in the digestion of proteinPart of gastric juice, it aids in the digestion of protein Sold commercially as “ Muriatic acid ”Sold commercially as “ Muriatic acid ”

Phosphoric Acid oA flavoring agent in sodas oUsed in the manufacture of detergents oUsed in the manufacture of fertilizers oNot a common laboratory reagent

Acetic Acid  Used in the manufacture of plastics  Used in making pharmaceuticals  Acetic acid is the acid present in vinegar

Acids Effect Indicators Blue litmus paper turns red in contact with an acid.

Acids Have a pH less than 7

Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl 2 + H 2 (g) Acids did not react with Copper, because copper is not an “ Active Metal ”

Acids React with Carbonates 2HC 2 H 3 O 2 + Na 2 CO 3 2 NaC 2 H 3 O 2 + H 2 O + CO 2

Effects of Acid Rain on Marble (calcium carbonate) George Washington: BEFORE George Washington: AFTER

What is a Base?  3 Major Definitions: Arrhenius, Bronsted-Lowry, and Lewis.  Arrhenius Base increases OH - concentration when in solution.  NaOH when disassociated produces: Na + & OH -  Bronsted-Lowry Bases are proton (H + ) acceptors.  NH 3 + HCl  NH Cl -  An Arrhenius base is always a B-L Base, but a B-L base is not always an Arrhenius base.

Properties of Bases  Bases taste bitter  Bases effect indicators  Red litmus turns blue  Phenolphthalein turns purple  Bases have a pH greater than 7  Bases are proton (hydrogen ion, H + ) acceptors  Solutions of bases feel slippery  Bases neutralize acids

Examples of Bases  Sodium hydroxide (lye), NaOH  Potassium hydroxide, KOH  Magnesium hydroxide, Mg(OH) 2  Calcium hydroxide (lime), Ca(OH) 2

Strong Bases vs. Weak Bases Strong bases are assumed to be 100% disassociated in solution. Are strong electrolytes! Weak acids are usually less than 5% disassociated in solution. Are Weak electrolytes! NaOH Ca(OH) 2 Cu(OH) 2 NH 3

Strong Base Dissociation NaOH Na + OH -

Weak Acid Dissociation OH - AgOH Ag + AgOH

Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

Bases have a pH greater than 7

Is H 2 O an acid or base?  HCl + H 2 O  H 3 O + + Cl -  H 2 O is an base! = proton acceptor  NH 3 + H 2 O  NH OH -  H 2 O is an acid! = proton donor  H 2 O can be either. This is called  Amphoteric = can act like an acid or base.

Ion Concentration in Water

pH- what is it?  pH is a measure of the H + or H 3 O + concentration.  The higher the concentration of H + or H 3 O +, the lower the pH.  Acids have higher [H 3 O + ], than pure water  pH range of an acid is  pH of pure water is 7

pOH- what is it?  pOH is a measure of the OH - concentration.  The higher the OH - concentration, the lower pOH.  Bases have higher OH - concentrations than pure water.  pH and pOH are exact opposites!  In a solution: when the [H 3 O + ] increases, [OH - ] decreases when pH increases, pOH decreases

Self-Ionization of Water H 2 O + H 2 O  H 3 O + + OH - pH explained

H+, OH-, and pH

pH Scale

How Do You Determine?  Described by an ionization equation:  Each acid and base will have either a high or low percent ionization  i.e. a high or low amount of the solution which dissociates into ions  The higher the percent ionization the stronger the acid HCl(aq) → [H] + + [Cl] –

pH  The pH is defined according to the following formula: pH = -log[H + ] and [H + ]=10 -pH  where [H + ] represents the concentration of hydrogen ions in mol/L

pOH  The pOH is defined according to the following formula: pOH = -log[OH - ] and [OH - ]=10 -pOH  Also note that pH + pOH= 14

pH and pOH is logarithmic  The pH and pOH scale is logarithmic, just like the Richter scale for earthquakes!  So a change of 1 pH means the concentration has changed by a factor of 10!

Acid and Base Strength For bases, a solution with a pH of 13 is: 10 times more basic than a solution with a pH of times more basic than a solution with a pH of 11 For acids, a solution with a pH of 3 is: 10 times more acidic than a solution with a pH of times more acidic than a solution with a pH of 5

Measuring pH with wide-range paper

Narrow-Range pH Paper

How Else Can We Measure Strength?  Scientists use a pH scale to represent how acidic or basic a solution is  pH means "power of hydrogen”

Practice Problems What is the pH of a 1.2 x HBr solution? What is the pOH of a 1.2 x HBr solution?

Practise Problems  What is the [H+] concentration in a solution with a pH of 7?  What is the [OH-] concentration in a solution with a pH of 12?

Indicators  The most common method to get an idea about the pH of solution is to use an acid base indicator  An indicator is a chemical that changes colour depending on the pH  A variety of indicators change color at various pH levels

Litmus paper  The most common indicator is found on "litmus" paper  It is red below pH 4.5 and blue above pH 8.2

Phenolphthalein  Phenolphthalein is a most common liquid indicator  It is clear below pH 8.5 and pink above pH 8.5

Other Indicators  Can also be obtained from many natural sources like strawberries, cabbage, tea and tulips

OTHER Tools  Basic indicators only show if a substance is acidic or basic, but not strength  Universal indicator are a mixture of indicators and can show strength of acid or base  So can a pH Meter