Identify the conjugate base for the following weak acids and calculate Kb for each. Which conjug

Identify the conjugate base for the following weak acids and...

Key Concepts

Inductive Effects in Acidity

Inductive effects involve the transmission of electron density through the sigma bonds in a molecule, influenced by electronegative atoms or groups attached to the acidic center. Electron-withdrawing groups, through the inductive effect, can stabilize the negative charge on the conjugate base, thereby increasing the acidity of the molecule and affecting the resulting base strength.

Conjugate Acid?Base Pairs

In acid-base chemistry, every acid has a corresponding conjugate base that forms when the acid donates a proton. This pairing is fundamental to understanding how acids and bases behave in solution and how equilibrium is maintained in acid-base reactions.

Acid and Base Strength

Acid strength refers to the tendency of an acid to donate a proton, while base strength is the ability of the conjugate base to accept a proton. In a conjugate pair, a weak acid yields a relatively stronger conjugate base compared to the conjugate base of a strong acid, which is typically very weak. Recognizing the intrinsic strengths of acids and their conjugate bases is crucial for predicting reaction outcomes.

Relationship between Ka and Kb

The equilibrium constants for acid and base reactions are interconnected by the water ionization constant (Kw), such that Ka × Kb = Kw. This relationship allows one to calculate the base dissociation constant (Kb) of a conjugate base if the acid dissociation constant (Ka) of the parent acid is known, forming a central concept in acid-base equilibrium analysis.

Transcript

00:01 But for this problem, we're given four different acids, and i'm already seeing a little mistake in whatever.

00:06 This is not an acid.

00:07 So for the following acids, determine their conjugate base.

00:11 Also, calculate the kv for each and decide which base of the four conduits is the strongest.

00:17 So first thing we're going to do is identify conjugate bases.

00:20 So, cl, ch2, c -o -o -h.

00:23 Anytime you see a c -o -h group, more than likely that's going to be your ionized acid group.

00:30 So writing that out, we have cl, ch2, c -o -o -0 -minus.

00:37 So that is our basic form.

00:40 That hydrogen has been ionized.

00:42 This is our base.

00:43 For our second one, we've got nh4 plus.

00:46 We know that nh4 plus is going to lose one of those hydrogens, leaving us with nh3.

00:51 That's our base for this one.

00:54 Hcn, there's only one ionizable portion of the compound that could give us acid.

01:00 So, cn minus, we remove that hydrogen.

01:04 And for ethanol, ch3, ch2oh, again, we only have one ionizable proton, and that's the one attached to oxygen.

01:18 So that's our list of bases.

01:22 Now we want to go through and find the kv for each of them.

01:28 So now we want to find kb.

01:29 Now, to do that, we're going to use this formula that i'm about to write out up here at the top for each of these.

01:34 Ka times kb equals kw.

01:40 When kw equals 1 times 10 to the negative 14.

01:44 Write this down now or at the end, come back and get it after watching the video once and no, this is the equation we're going to use to find the kb for each of these conjugate pairs.

01:57 So knowing this, we can plug in our values.

02:02 So i'll do that in red on.

02:06 I'll do it in black.

02:07 Okay, so we've got ka times kb equals kw.

02:10 Well, we're given ka, so we're going to solve for kv.

02:14 We plug in our values.

02:17 So this is our ka equals kw.

02:21 So if we solve this out, we divide this by 1 times, or no, 1 .4 times 10 to the negative third.

02:30 So we divide that to get kv by itself, and we'll do this for each of these.

02:34 They're all going to be the exact same format, and that will give us our kv value for this first one.

02:43 Of 7 .14 times 10 to the negative 12...