CA0426C Mono & Polyprotic Acids. CA-0426: Mono & Polyprotic Acids 1) - You may now know that HCl and HF are (acids) because they can (donate) a (hydrogen

CA0426C

Mono & Polyprotic Acids

CA-0426: Mono & Polyprotic Acids

1) - You may now know that HCl and HF are (acids) because they can (donate) a (hydrogen ion) = a “proton”; in an acid-base reaction.

p⁺

Hydrogen atom

9p⁺

Fluorine atom

H₂O - Added

Ion (H⁺)“Proton”

9n°

Fluorine anion F⁻


2) - From their chemical formulas (HCl and HF) you can see that EACH “acid” can donate only (one) hydrogen ion. This is called a (monoprotic) acid [where “mono” means “one” and “protic” means “proton”.]

p⁺

Hydrogen atom

9p⁺

Fluorine atom

H₂O - Added

Ion (H⁺)“Proton”

9n°

Fluorine anion F⁻


3) - Other monoprotic acids are:Perchloric acid (HClO4);Nitric acid (HNO3);(Hydrobromic) acid (HBr) and;Acetic acid (which is a/k/a ethanoic acid) (CH3COOH)

CA-0426: Mono & Polyprotic AcidsOther monoprotic acids are:Perchloric acid (HClO4);Nitric acid (HNO3);(Hydrobromic) acid (HBr) and;Acetic acid (which is a/k/a ethanoic acid) (CH3COOH)

4) - Given the four listed monoprotic acids above in statement (3) – go back and highlight in red color the hydrogen atom in each that will be donated in an “acid-base” pair reaction.

CA-0426: Mono & Polyprotic AcidsAcetic acid (which is a/k/a ethanoic acid) (CH3COOH)

5) - Looking at the ethanoic acid molecule CH3COOH (also known as acetic acid) you can see it contains (four) hydrogen atoms. Can ethanoic acid donate (more than) one hydrogen ion? (NO); it contains only one (ionizable) hydrogen atom.


6) - Only one of the four hydrogen atoms in the CH3COOH molecule can be (donated) because only those hydrogen atoms bonded to (electronegative) elements by (polar) bonds are ionizable [and therefore; can be donated as an acid does.]

Electronegativity – The bigger the difference…… the bigger the ability to “hang onto” electron(s) & strong tendency to “dissociate” (break apart) in

water.

Oxygen (O) > Hydrogen (H)

Carbon (C) ≈ Hydrogen (H)


H-F

7) - In an HF (hydrofluoric acid) molecule, the hydrogen atom is bonded to a fluorine atom, which has the (highest) electronegativity of all the elements.


water.

Fluorine (F) >> Hydrogen (H)


8) - In CH3COOH (ethanoic acid) – three of the four hydrogens are bonded to a carbon atom which have almost the same (electronegativity) as hydrogen meaning they are nearly equal. Only the hydrogen atom bonded to the electronegative (oxygen) atom can be donated.


water.

Oxygen (O) > Hydrogen (H)

Carbon (C) ≈ Hydrogen (H)


9) - Some acids do donate (more than) one hydrogen ion. For example:(Sulfuric) acid H2SO4

Carbonic acid (H2CO3)

S OOH H

O

O

C

O

OO

H

H


9) - Can each donate (two) hydrogen ions. In each… both [of the] hydrogen atoms are attached to (oxygen) atoms [which are higher electronegativity than hydrogen].

(Sulfuric) acid H2SO4


S OOH H

O

O

C

O

OO

H

H


10) - Acids that contain two ionizable hydrogen atoms per (molecule) are called (di)protic acids.

(Sulfuric) acid H2SO4


S OOH H

O

O

C

O

OO

H

H


11) - In a similar way, acids that contain (three) ionizable hydrogen atoms per molecule allowing them to donate three hydrogen (ions) or protons are called (tri)protic acids.

Phosphoric acid (H3PO4)(Boric) acid H3BO3

P OOH H

O

O

B

O

OO

HH

H H


12) - The term polyprotic acid can be used for any acid that has more than (one) ionizable hydrogen (atom).

Phosphoric acid (H3PO4)(Carbonic) acid H2CO3

P OOH H

O

O

C

O

OO

H

H

H


13) - All polyprotic acids ionize in (steps) …[the number of “steps” = to the number of ionizable

hydrogen atoms]. Eg. Phosphoric acid-Dissociated & Ionized in water

P OOH H

O

O

OHH

H



hydrogen atoms]. STEP 1

P OOH H

O

O

OHH

H




P OOH

O

O

OHH

H




P OOH

O

O

OHH

CA-0426: Mono & Polyprotic Acids - Anhydrides

14) - Some (oxides) can become acids or bases by adding the elements contained in water. These compounds are called (anhydrides). Oxides of (non-metallic) elements such as (carbon), (sulfur), or (nitrogen), produce an (acid) in aqueous solution.

C

O

O

O

HH


14) - Oxides of (metallic) elements usually form (basic) solutions.

Ca

O

O

HH


Eg. carbon di(oxide), an oxide of the non-metal carbon – forms an aqueous solution of (carbonic) acid.

CO2 (g) + H2O (l) H2CO3 (aq)

C

O

O

O

HH

C

O

O

O

HH


14) - Eg. calcium (oxide), an oxide of the metal calcium – forms an aqueous solution of calcium (hydroxide).

CaO(s) + H2O (l) Ca+2 (aq) + 2OH— (aq)

Ca

O

O

HH


Similarly, SO3 is the (anhydride) of H2SO4 [sulfuric acid]

Similarly, MgO is the (anhydride) of Mg(OH)2 [magnesium hydroxide]

S

O O

O

Mg

O

NON-metal Metal

base


Pg. 601 prob. 3 – list the steps of ionization of the mono/polyprotic acids:

a)H2Se

STEP 1: H2Se(aq) + H20(l) H3O+ (aq) + HSe— (aq)

Step 2: HSe— (aq) + H20(l) H3O+ (aq) + Se—2

(aq)



b)H3AsO4

Step 1: H3AsO4 (aq) + H20(l) H3O+ (aq) + H2AsO4 -- (aq)

Step 2: H2AsO4 -- (aq) + H20(l) H3O+ (aq) + HAsO4

--2 (aq)

Step 3: HAsO4

--2 (aq) + H20(l) H3O+ (aq) + AsO4 --3 (aq)



C) H2SO3

Step 1: H2SO3 (aq) + H20(l) H3O+ (aq) + HSO3 -- (aq)

Step 2: HSO3 -- (aq) + H20(l) H3O+ (aq) + SO3

--2 (aq)


Pg. 601 prob. 9 – In the structural formula below… identify any hydrogen atoms that are likely to be ionizable:

C C C

O

O

O

OH

HH

H

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CA0426C Mono & Polyprotic Acids. CA-0426: Mono & Polyprotic Acids 1) - You may now know that HCl and HF are (acids) because they can (donate) a (hydrogen