exam III chp 17 & 18

polyprotic and diprotic acids/bases. Why is the 2nd dissociation constant of a weak diaprotic acid smaller than the first?

(1) the removal of H_ from anion is difficult compared to a neutral atom. (2) higher stability of conjugate base (lower charge density).

polyprotic bases

A compound that can accept more than one proton.

Increasing acidity; "place in order of increasing acid strength".

Acid strength depends on strength of H−X bond, weaker the bond easily to give H+. Ex: HCLO2, HCLO, HCLO3, HCLO4 (HCLO4 has the largest acid strength, bc it has more O molecules than the rest that will take far more strength to actually disassociate like the others)

bronsted-lowry

Acid, electron pair acceptor. Base, electron pair donor.

lewis

Acid, electron pair electrons. Base, electron pain donor.

solns with the best buffering capacity?

Amount of strong acid or base that must be added to buffer soln. to change Ph. the buffer capacity of a buffer soln. is higher when the log of ratio of concentrations for conjugate base and weak acid is as low as possible.

Increases hydrogen ion concentration in aqueous solution

Arrhenius ACID

Compare & contrast: Arrhenius and Brønsted-Lowry theories

Arrhenius, H+/H3O+ in H2O for acid (Any substance that dissolves to form H+ in aqueous solution. ), OH- in H2O (dissociates to form OH-_). Bronsted-Lowry Acid, any substance that donates a proton to another substance (soln. that has a proton that can potentially be removed). BL base, any substance that receives a proton (or potentially removes it from the acid). Both acids have a compound that breaks down to give an H+ in solution. The only difference is that the bronsted-lowry acid does not have to be dissolved in water.

the higher the ph, the higher the percent ionization because:

As the concentration of a weak acid decreases, the percent ionization increases (the assumption that x is small is less likely to be valid). The lower the concentration of an acid (either weak or strong), the higher the pH.

All the following pair of compounds can be used to prepare buffer solutions: CH3NH2/CH3NH3Cl, NH3/NH4NO2, H3PO4/NaH2PO4, NaF/HF, and NaHCO3/Na2CO3

FALSE. Buffers need to be composed of certain pairs of solutes: either a weak acid plus a salt derived from that weak acid, or a weak base plus a salt of that weak base

a 0.38 M soln. of Ca(NO3)3 is acidic.

False! -log(3.8)=0.42, 14.00-0.42= BASIC

the sharpness of the titration graphs of weak acids with strong base is independent of the Ka's of weak acids and only depends on the weak acid concentrations

False! the sharpness of the titration graphs of WA's with SB's is actually dependent on both the Ka's and temp (pH indicators change).

ion formed by the association of water molecule with a proton that has been donated by an acid

H3O+

most acidic pH

H3O+ concentration increases with increasing weak acid concentration. -log(highest number) to give 0

triprotic acid

H3PO4; symbolized as H30

Which of the following acids will have the strongest conjugate base? a. HCl b. HClO4 c. H2SO4 d. HCN e. KBr

HCN

Which one of the following is the strongest acid? a. HCN b. C6H5OH c. HCl d. HClO e. HF

HCl

diprotic acid

HOOC-CH = CH-COOH (H2A) or carbonic acid (H2CO3) (again H2A)

phosphate anion; possibly obtained by dissolving Na3PO4 in water.

PO4^3- (tribasic). Can accept 3+ protons in an acid base rxn.

Understand the meaning and implication of the ion product constant of water; Kw = [H3O+][OH-]=1.0 X 10-14 at 25 °C and its -log format, pH + pOH = 14.00.

The auto ionization of water.

need to find the lowest PH quickly?

The largest Ka value of the acid bunch is closest to 14.00 base-level. Ex: 1.1*10^-2 = 14.00-1.95=12.05

the human blood Ph is maintained at a remarkably constant pH level of 7.45 bc of the presence of several buffer systems that include BICARBONATE/CARBONIC ACID

True

both the initial pH and the pH @ 50% titration completion of a weak acid with a strong base ca. be used to calculate the dissociation constant of the weak acid.

True.

the calculated pH using the henderson-hasselbalch equation becomes unreliable when the Ka value becomes large and the concentrations of the buffer components become very small.

True.

For oxyacids (molecules with O), acid strength increases with increasing electronegativity of the atom bonded to the oxygen atoms. The electronegativity trend is Cl > Br > I, so chlorous acid is the strongest acid (largest Ka).

Which acid has the largest Ka: HClO2(aq), HBrO2(aq), HIO2(aq)?

Three of the following acids are weak acids (2-7 pH & low concentration) : HF, HI, HClO4, H2SO4, HCN, HBr, HNO3, HNO2

Yes, HF, HCN,HNO2

Amphiprotic

a substance that can act as either an acid or a base. Examples of a ... substances include water, amino acids, proteins, and many metal oxides and hydroxides. Oxides and hydroxides of aluminum, antimony, arsenic, antimony, bismuth, beryllium, chromium, cobalt, copper, gallium, germanium, gold, iron, lead, silver, tellurium, tin, and zinc are...

Polyfunctional acids and bases are capable of

accepting or donating two or more protons

Arrhenius

acid increases the concentration of H+ ions in aqueous solution, while base increases the concentration of OH- ions in aq soln. Must have an H. Acid, substance when dissoved in water procudes H+ or H3O+ ion. Base, substance when dissoved in water produces OH-ions

A substance that can behave as both an acid and a base

amphoteric

process by which water acts as an acid and a base within itself

auto-ionization

bases are unique because

bitter, slippery, red litmus paper blue

polyprotic acids

capable of 2+ ionizable protons. In water, undergo (successive) dissociation w ea step having its own Ka (acid dissociation constant; used to decipher strong acids from weak acids)

CO3^2-

diabasic. Possibly obtained by dissolving Na2CO3 in water. Can accept two protonns in an acid base rxn.

The %ionization of strong acids increases with increasing concentration

false

the conjugate base of a very weak acid is weaker than the conjugate base of a strong acid

false. the conjugate base of a very weak acid is actually stronger than the conjugate base of a strong acid. Bc the stronger the acid, the weaker its conjugate base.

greatest percent ionization

percent ionization increases as weak acid concentration decreases. (tiniest number)

acids are unique because

sour, dissolve some metals, ability to neutralize bases, blue litmus paper to red. ex: lemons, vinegar

amphoteric, autoprotoloysis

species with both acidic and basic properties. Because of this property, water can act as an acid or as a base with itself. One water molecule will act as an acid and another water molecule will act as a base. This reaction is called autoionization or self ionization

In general, the stronger the acid, the weaker its conjugate base.

true

pH and pOH are logarithmic scales

true

the common ion effect causes the percent ionization of a weak acid to decrease when the weak acid is present as a component in a weak acid /conjugate base buffer.

true