Acids and Bases

Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

Acid Nomenclature Review No Oxygen  w/Oxygen An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

Arrhenius acid is a substance that produces H + in water Arrhenius base is a substance that dissociate in water to produce hydroxide ions, OH - Acid/Base definitions Definition 1: Arrhenius HCl (aq) H + (aq) + Cl - (aq) NaOH (aq) Na + (aq) + OH - (aq) Problems: Some substances acted as bases and didn’t contain hydroxide ions (OH) ex: NH 3, Na 2 CO 3 This only works when water is the solvent!

Acid/Base Definitions Definition #2: Brønsted – Lowry (our focus)Definition #2: Brønsted – Lowry (our focus) Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost its electron! A donor needs an acceptor so the acid and The base must always be present together. Acid-base pairs!

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor acid conjugate base base conjugate acid

ACID-BASE THEORIES The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID

Conjugate Pairs Acid and its conjugate base are linked by a transfer of H +

Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH -  Cl - + H 2 O H 2 O + H 2 SO 4  HSO H 3 O + AcidAcid AcidAcid BaseBase BaseBase Conj. Base Conj. Acid

Acids & Base Definitions Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair Definition #3 – Lewis

The pH scale is a way of expressing the concentration of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base

Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X pH = - log 1 X pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

Try These! Find the pH of these: 1)A 0.15 M solution of Hydrochloric acid 2) A 3.00 X M solution of Nitric acid pH = - log [H+] pH = - log 0.15 pH = - (- 0.82) pH = 0.82 pH = - log 3 X 10-7 pH = - (- 6.52) pH = 6.52

pH calculations – Solving for H+ If the pH of Coke is 3.12, [H + ] = ??? Because pH = - log [H + ] then - pH = log [H + ] - pH = log [H + ] Take antilog (10 x ) of both sides and get 10 -pH = [H + ] [H + ] = = 7.6 x M *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

More About Water H 2 O can function as both an ACID and a BASE. In pure water there can be AUTOIONIZATION Equilibrium constant for water = K w K w = [H 3 O + ] [OH - ] = 1.00 x at 25 o C

More About Water K w = [H 3 O + ] [OH - ] = 1.00 x at 25 o C In a neutral solution [H 3 O + ] = [OH - ] and so [H 3 O + ] = [OH - ] = 1.00 x M Autoionization

pOH Since acids and bases are opposites, pH and pOH are opposites!Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH.pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a basepOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

pH [H + ] [OH - ] pOH

[H 3 O + ], [OH - ] and pH What is the pH of the M NaOH solution? [OH-] = (or 1.0 X M) pOH = - log pOH = - log pOH = 3 pOH = 3 pH = 14 – 3 = 11 OR K w = [H 3 O + ] [OH - ] [HO + ] = 1.0 x M [H 3 O + ] = 1.0 x M pH = - log (1.0 x ) = 11.00

What is the pH of a 2 x M HNO 3 solution? HNO 3 is a strong acid – 100% dissociation. HNO 3 (aq) + H 2 O (l) H 3 O + (aq) + NO 3 - (aq) pH = -log [H + ] = -log [H 3 O + ] = -log(0.002) = 2.7 Start End M 0.0 M What is the pH of a 1.8 x M Ba(OH) 2 solution? Ba(OH) 2 is a strong base – 100% dissociation. Ba(OH) 2 (s) Ba 2+ (aq) + 2OH - (aq) Start End M M0.0 M pH = – pOH = log(0.036) = 12.56

End of section 8.1 Homework page 503