For this problem, I am mainly confused as to how you tell which one is an acid o
ID: 530128 • Letter: F
Question
For this problem, I am mainly confused as to how you tell which one is an acid or a base, and which one is the strong or weak acid or base. Some of these compounds are not in the table, so I do not get how you are supposed to tell.
TABLE15 Relative Strength of Some Common Organic and inorganic Acids and Their Conjugate Bases Conjugate Base PR. chloride bases hydrothlreic aid 55.6 H40 CH -C-OH HO 474 6.0 x 10 922 5.8 x 10 924 t Hito NH hydroxide ion 1.3 x 10-16 5.9 CH CH CH/CH HOV (a) HCOOH CNT (b) CH3COO CH3OH (c) CH3OH NaNH (d) NaOCH3 HCN (e) HC H20 (f) H30 CHOExplanation / Answer
The easier way to predict the direction of an acid-base reaction is to remember that an acid-base reaction will always proceed in the direction of the weaker acid or weaker base. Therefore, a stronger acid and base will react to form a weaker acid and weaker base.
Another point to note is that the higher the pKa value of an acid, the weaker is the acid and viceversa.
a) HCOOH + CN- <=====> HCOO- + HCN
pKa = 3.76 9.22
HCOOH is a stronger acid (lower pKa) while HCN is a weaker acid (higher pKa). The equilibrium favors the products as per the above discussion.
b) CH3OH + NaNH2 <======> CH3ONa + NH3
pKa = 16 33
CH3OH is comparatively a stronger acid while NH3 is a weaker acid. The equilibrium favors the products.
c) HCl + H2O <=======> Cl- + H3O+
pKa = -7 -1.7
A stronger acid (HCl) forms a weaker acid (H3O+) and the equilibrium favors the products.
d) CH3COO- + CH3OH <======> CH3COOH + CH3O-
pKa = 16 4.74
A weaker acid (CH3OH) forms a stronger acid (CH3COOH) and hence the equilibrium favors the reactant side. In other words, the acid-base reaction is not favored.
e) NaOCH3 + HCN <======> NaCN + CH3OH
pKa = 3.76 16
A stronger acid (HCN) forms a weaker acid (CH3OH) and the equilibrium favors the product side.
f) H3O+ + CH3O- <=======> H2O + CH3OH
pKa = -1.7 16
Since the product side contains a weaker acid (CH3OH), the equilibrium favors the products.
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