The Chemistry of Acids and Bases To play the movies and simulations included, view the presentation in Slide Show Mode.

Learning Objectives 12.1C: Acids and bases Learners be able to calculate, recognize, and understand 1) acidity/alkalinity in aqueous solution that Arrhenius and Bronsted-Lowry are equivalent 2) proton donors and bases are proton acceptors 3) pH as -log10[H+], and be able to convert pH to concentration and the reverse pH for a strong acid be able to calculate the pH of a strong acid and a strong base 4) know that water is weakly dissociated 5) know the ionic product of water, Kw and that Kw = [H+] [OH-]

New Terms Hydronium Ion which is (H3O+) pH = Log 10 or power of H+ Amphiprotic like frogs or writing with both hands 4) Conjugate = Latin word conjugare, like conjoined

Acids

Bases

Some Operational Properties of Acids Produce H+ Taste sour. Ex: Vinegar is acetic acid and citrus fruits contain citric acid Corrode metals and produce hydrogen gas Electrolytes React with carbonates and bicarbonates to produce CO2(g) React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red “Blue to Red A-CID”

How can we identify strong acids or bases? Easy, memorize them! Strong Acids and Bases How can we identify strong acids or bases? Easy, memorize them! Memorized Strong Acids HClO4 H2SO4 HI HBr HCl HNO3

https://www.youtube.com/watch?time_continue=1&v=ZiokqP0aZ1E

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

Acid Nomenclature Review HBr (aq) H2CO3 H2SO3  hydrobromic acid  carbonic acid  sulfurous acid

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”

ALL Strong Bases become Some Common Bases NaOH sodium hydroxide lye KOH potassium hydroxide liquid soap Ba(OH)2 barium hydroxide stabilizer for plastics Mg(OH)2 magnesium hydroxide MOM” Milk of magnesia Al(OH)3 aluminum hydroxide Maalox (antacid) ALL Strong Bases become OH-

Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H+ ions Bases – produce OH- ions (Problem: some bases don’t have hydroxide ions!)

Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water

Arrhenius: acids and bases Acid: Substance that, when dissolved in water, increases the concentration of hydrogen ions (protons, H+). Base: Substance that, when dissolved in water, increases the concentration of hydroxide ions or OH-

How can we identify strong acids or bases? Strong Acids and Bases How can we identify strong acids or bases? HCl HNO3 HI HBr HClO4 H2SO4 YOU DO THE REST

Definitions #2 Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

B/L Acid is a substance that produces H+ (H3O+) in water A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor Lowry Bronsted B/L base is a substance that produces OH- in water. A Brønsted-Lowry base is a proton acceptor base conjugate acid conjugate base acid

When there is NO charge The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID…must have a removable (acidic) proton. HCl, H2O, H2SO4 A Brønsted–Lowry BASE…must have a pair of nonbonding electrons, or a negative charge.NH3, H2O, SO3-2

If it can be either… ...it is amphiprotic. HCO3– HSO4 – H2O

Water, Water Everywhere Autoionization Kw = [H3O+] [OH-] = 1.00 x 10-14 at 25 oC In a neutral solution [H3O+] = [OH-] so Kw = [H3O+]2 = [OH-]2 and so [H3O+] = [OH-] = 1.00 x 10-7 M

pH of Common Substances

pH pH is defined as the negative base-10 logarithm of the hydronium ion concentration. pH = –log [H3O+]

(Remember that the [ ] mean Molarity, or mol/L) Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity, or mol/L) Example: If [H+] = 1 X 10-10 pH = - log 1 X 10-10 pH = - (- 10) pH = 10 Example: If [H+] = 1.0 X 10-5 pH = - log 1.0 X 10-5 pH = - (- 5) pH = 5

A pH Number line Number lines have been used in history and math classes, so to keep up we use them in chemistry classes. [H+] =10-15 [OH -] = 101 [H+] < [OH -] basic pH = 15 [H+] =10-12 [OH -] = 10-2 basic pH = 12 [H+] < [OH -] basic [H+] = 10-7 [OH -] = 10-7 [H+] = [OH -] neutral pH = 7 acidic [H+] = 10-2 [OH -] = 10-12 [H+] > [OH -] acidic pH = 2

Try These! Find the pH of these: A 0.15 M solution of Hydrochloric acid Answer: pH 0.82 (- 2 sig figs) 2) A 3.00 X 10-7 M solution of Nitric acid Answer: pH 6.523 (- 3 sig figs) remember leading zero do NOT count

pH calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ??? Because pH = - log [H+] then - pH = log [H+] Take antilog (10x) of both sides and get 10-pH = [H+] [H+] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button

pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? pH = - log [H+] 8.5 = - log [H+] -8.5 = log [H+] Antilog -8.5 = antilog (log [H+]) 10-8.5 = [H+] 3.16 X 10-9 = [H+]

The “other” “p” Scale The “p” in pH tells us to take the negative log of the quantity (in this case, hydronium ions). Some similar examples are pOH –log [OH-]

pOH Acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH. No one uses the scale pOH looks at the perspective of a base pOH = - log [OH-] Since pH and pOH are on opposite ends, pH + pOH = 14

[H3O+], [OH-] and pH What is the pH of the 0.0010 M NaOH solution? [OH-] = 0.0010 (or 1.0 X 10-3 M) pOH = - log 0.0010 pOH = 3 pH = 14 – 3 = 11 OR Kw = [H3O+] [OH-] [H3O+] = 1.0 x 10-11 M pH = - log (1.0 x 10-11) = 11.00

If you know one, you know them all: [OH-] 1.0 x 10-14 [OH-] 10-pOH 1.0 x 10-14 [H+] -Log[OH-] [H+] pOH 10-pH 14 - pOH -Log[H+] 14 - pH pH

Calculating [H3O+], pH, [OH-], and pOH Problem 1: A chemist dilutes concentrated hydrochloric acid to make a solution of 0.0024 M. Calculate the [H3O+], pH, [OH-], and pOH ANSWERS: pH=2.62, pOH = 11.38, 4.2x10 -12 Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral? ANSWERS : An acid. [H3O+], 0.00021 M, [OH-], 4.7x10-11 pOH = 10.33

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